RU2838596C2 - Electrically controlled aerosol generating system and electric circuit therefor, as well as heater assembly, electrically controlled aerosol generating device, method for controlling power supply to electric heater and computer-readable data medium - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: group of inventions relates to an electrically controlled aerosol generating system and an electrical circuit therefor, as well as a heater assembly, an electrically controlled aerosol generating device, a method for controlling power supply to an electric heater and a computer-readable data medium. Electrically controlled aerosol-generating system comprises an electric heater comprising at least one heating element for heating an aerosol-forming substrate, power supply unit and electric circuit connected to electric heater and power supply unit and containing memory device. Electric circuit is made with possibility of: measuring initial electric resistance of electric heater; measuring subsequent electrical resistance of the electrical heater after measuring the initial electrical resistance; determining the difference between the initial electrical resistance and the subsequent electrical resistance; determining an unfavourable condition when a certain difference between the subsequent electrical resistance and initial electrical resistance is greater than the maximum threshold value or less than the minimum threshold value stored in the memory; and controlling the power supplied to the electric heater, based on whether the presence of an unfavourable condition is determined, or providing an indication if the presence of an unfavourable condition is determined, wherein difference between initial electrical resistance and subsequent measurements of electrical resistance is constantly monitored to determine, whether this difference between user puffs on the aerosol generating system is less than the cooling threshold value; and, if it is determined that between the user's puffs in the aerosol generating system, the difference is not less than the cooling threshold value, electric circuit allows preventing or limiting the supply of energy to the heater until the difference falls below the threshold value of cooling.

EFFECT: enabling determination of whether the consumable part is "authentic" or is a consumable part which is considered to be compatible with the device by the device manufacturer.

15 cl, 12 dwg

Description

The present invention relates to controlling a heater. Specific disclosed examples relate to controlling a heater in an electrically heated aerosol generating system. Aspects of the present invention are directed to an electrically heated aerosol generating system and a method of operating an electrically heated aerosol generating system. Some disclosed examples relate to a system that can detect abnormal changes in the electrical resistance of a heating element, which may indicate unfavorable conditions on the heating element. Unfavorable conditions may, for example, indicate depletion of the level of aerosol-forming substrate in the system. In some disclosed examples, the system may be effective with heating elements of different electrical resistance. In other examples, the detected electrical resistance parameters may be used to determine or select how the system may function. Some aspects and features of the present invention may be applicable to electrically heated smoking systems.

Document WO 2012/085203 discloses an electrically heated smoking system comprising a liquid storage portion for storing a liquid aerosol-forming substrate; an electric heater comprising at least one heating element for heating the liquid aerosol-forming substrate; and an electrical circuit configured to determine the exhaustion of the liquid aerosol-forming substrate based on the relationship between the power supplied to the heating element and the resulting change in the temperature of the heating element. In particular, the electrical circuit is configured to calculate the rate of increase in the temperature of the heating element, wherein a high rate of increase in temperature indicates drying of the wick that transfers the liquid aerosol-forming substrate to the heater. The system compares the rate of increase in temperature with a threshold value stored in a memory device during manufacture. If the rate of increase in temperature exceeds the threshold value, the system may stop supplying power to the heater.

In the system of WO 2012/085203, the electrical resistance of the heating element can be used to calculate the temperature of the heating element, which has the advantage that a special temperature sensor is not required. However, the system still requires storing a threshold value that depends on the resistance of the heating element and is therefore optimized for heating elements having a specific electrical resistance or resistance range.

However, it may be desirable for the system to operate with different heaters. Typically, in a system of the type described in WO 2012/085203, the heater is provided in a disposable cartridge together with a source of liquid substrate that forms an aerosol. The heating elements in different cartridges may have different electrical resistances. This may be a result of manufacturing tolerances in cartridges of the same type, or because different cartridge designs are available for use in the system to provide different user sensations. The system of WO 2012/085203 is optimized for a heater having a known specific electrical resistance used in the system, which is determined during manufacture of the system.

It would be desirable to have an alternative system for detecting heater dryout or other adverse conditions on the heater in an electrically heated aerosol generating system, and in particular a system that can operate with different heaters.

In electrically heated aerosol generating systems having a permanent device portion and a consumable portion that contains an aerosol-forming substrate, it would also be desirable to be able to readily determine whether the consumable portion is "genuine" or is a consumable portion that is considered compatible with the device by the device manufacturer. This is true for systems in which the heater is part of the consumable portion as well as for systems in which the heater is part of the permanent device.

According to a first aspect of the present invention, there is provided an electrically controlled aerosol generating system comprising:

an electric heater comprising at least one heating element for heating an aerosol-forming substrate;

power supply; and

an electrical circuit connected to an electric heater and a power supply and containing a storage device, wherein the electrical circuit is configured to:

measuring the initial electrical resistance of an electric heater;

measuring the subsequent electrical resistance of an electric heater after measuring the initial electrical resistance;

determining the difference between the initial electrical resistance and the subsequent electrical resistance;

determining an unfavourable condition when a determined difference between the subsequent electrical resistance and the initial electrical resistance is greater than a maximum threshold value or less than a minimum threshold value stored in a memory device; and

controlling the power supplied to the electric heater based on whether an unfavorable condition is determined to exist, or providing an indication if an unfavorable condition is determined to exist.

One of the unfavorable conditions in an aerosol generating system or an aerosol generating device is insufficient or exhausted aerosol forming substrate on the heater. In general, the less aerosol forming substrate is delivered to the heater for evaporation, the higher the temperature of the heating element will be for a given supplied feed. For a given feed, the process of changing the temperature of the heating element during a heating cycle or the development of this process of changing over several heating cycles can be used to detect whether the amount of aerosol forming substrate on the heater has been exhausted and, in particular, whether the heater has insufficient aerosol forming substrate.

Another unfavorable condition is the presence of a counterfeit or incompatible heater or a damaged heater in a system that has a reproducible or disposable heater. If the resistance of the heating element increases faster than expected for a given supply, it may be because the heater is counterfeit and has different electrical properties than the genuine heater, or it may be because the heater is damaged in some way. In either case, the electrical circuit may be designed to prevent power from being supplied to the heater.

Another unfavorable condition is the presence of counterfeit, incompatible, old or damaged aerosol forming substrate in the system. If the resistance of the heating element increases faster than expected for a given power supply, it may be due to the aerosol forming substrate being counterfeit or old and therefore having a higher or lower moisture content than expected. For example, if a solid aerosol forming substrate is used, if it is very old or has not been stored properly, it may become dry. If the substrate is drier than expected, less energy will be used for evaporation than expected and the temperature of the heater will increase faster. This will cause an unexpected change in the electrical resistance of the heating element.

By using the difference between the initial resistance measurement and the subsequent resistance of the electric heater, the system does not need to determine the actual temperature of the heating element or have any previously stored information about the resistance of the heating element at a given temperature. This allows different approved heaters to be used in the system and allows for deviations in the absolute resistance of the same type of heater due to manufacturing tolerances without causing an unfavorable condition. It also allows for the detection of an incompatible heater.

The electrical circuit may be configured to measure the initial electrical resistance of the heating element and the electrical resistance of the heating element at a time after the initial power supply to the electric heater from the power supply. The initial electrical resistance may be measured before the first use of the heater. If the initial resistance is measured before the first use of the heater, it may be assumed that the heating element is at approximately room temperature at the time of measurement. Since the expected change in resistance over time may depend on the initial temperature of the heating element, measuring the initial resistance at or near room temperature allows for narrower ranges of expected behavior to be established.

The initial resistance can be calculated as the initial measured resistance minus the expected parasitic resistance due to the presence of other electrical components and electrical contacts within the system.

The system may comprise a device and a cartridge removably coupled to the device, wherein the power supply and the electrical circuit are in the device, and the electrical heater and the aerosol-forming substrate are in the removable cartridge. In this context, a cartridge "removably coupled" to the device means that the cartridge and the device can be connected and disconnected from each other without significant damage to either the device or the cartridge.

The electrical circuit may be configured to detect the insertion and removal of the cartridge from the device. The electrical circuit may be configured to measure the initial electrical resistance of the heater when the cartridge is initially inserted into the device, but before significant heating has occurred. The electrical circuit may compare the measured initial resistance with a range of acceptable electrical resistance stored in the memory device. If the initial resistance is outside the acceptable resistance, it may be considered counterfeit, incompatible, or damaged. In this case, the electrical circuit may be configured to prevent power from being supplied until the cartridge is removed and replaced with another cartridge.

Cartridges with different properties can be used with the device. For example, two different cartridges with different sized heaters can be used with the device. The larger heater can be used to deliver more aerosol to users with such personal preference.

The cartridge may be refillable or may be designed to be removed when the aerosol-forming substrate is exhausted.

An aerosol-forming substrate is a substrate capable of releasing volatile compounds that can form an aerosol. The volatile compounds can be released by heating the aerosol-forming substrate.

The aerosol-forming substrate may comprise a material of plant origin. The aerosol-forming substrate may comprise tobacco. The aerosol-forming substrate may comprise a tobacco-containing material comprising volatile tobacco aromatic compounds that are released from the aerosol-forming substrate upon heating. The aerosol-forming substrate may alternatively comprise a material that does not contain tobacco. The aerosol-forming substrate may comprise a homogenized material of plant origin. The aerosol-forming substrate may comprise a homogenized tobacco material. The aerosol-forming substrate may comprise at least one aerosol-forming substance. The aerosol-forming substance is any suitable known compound or mixture of compounds that, when used, facilitates the formation of a dense and stable aerosol and is substantially resistant to thermal degradation at the operating temperature of the system. Suitable aerosol formers are well known in the art and include, but are not limited to: polyhydric alcohols such as triethylene glycol, 1,3-butanediol and glycerol; esters of polyhydric alcohols such as glycerol mono-, di- or triacetate; and aliphatic esters of mono-, di- or polycarboxylic acids such as dimethyl dodecanedioate and dimethyl tetradecanedioate. Preferred aerosol formers are polyhydric alcohols or mixtures thereof such as triethylene glycol, 1,3-butanediol and, most preferably, glycerol. The aerosol-forming substrate may contain other additives and ingredients such as fragrances.

The cartridge may contain a liquid aerosol-forming substrate. For the liquid aerosol-forming substrate, certain physical properties, such as the vapor pressure or viscosity of the substrate, are selected to be suitable for use in an aerosol-generating system. The liquid preferably contains a tobacco-containing material containing volatile tobacco aromatic compounds that are released from the liquid upon heating. Alternatively or additionally, the liquid may contain a non-tobacco material. The liquid may include water, ethanol or other solvents, plant extracts, nicotine solutions, and natural or artificial flavors. Preferably, the liquid further contains an aerosol-forming agent. Examples of suitable aerosol-forming agents are glycerol and propylene glycol.

The advantage of providing a liquid storage portion is that the liquid in the liquid storage portion is protected from the surrounding air. In some embodiments, ambient light also cannot penetrate into the liquid storage portion, so that deterioration of the liquid properties caused by light can be avoided. Moreover, a high level of hygiene can be maintained.

Preferably, the liquid storage portion is designed to hold liquid for a given number of puffs. If the liquid storage portion is non-refillable and the liquid in the liquid storage portion has been used up, the liquid storage portion must be replaced by the user. During such replacement, it is necessary to prevent contamination of the user with the liquid. Alternatively, the liquid storage portion may be refillable. In this case, the aerosol generating system may be replaced after a certain number of refills of the liquid storage portion.

Alternatively, the aerosol-forming substrate may be a solid substrate. The aerosol-forming substrate may comprise a tobacco-containing material comprising volatile tobacco aroma compounds that are released from the substrate upon heating. Alternatively, the aerosol-forming substrate may comprise a non-tobacco material. The aerosol-forming substrate may further comprise an aerosol-forming agent. Examples of suitable aerosol-forming agents include glycerol and propylene glycol.

If the aerosol-forming substrate is a solid aerosol-forming substrate, the solid aerosol-forming substrate may comprise, for example, one or more of the following: powder, granules, pellets, grains, thin tubes, strips or sheets containing one or more of the following: grass leaves, tobacco leaves, tobacco rib fragments, reconstituted tobacco, homogenized tobacco, extruded tobacco, molded leaf tobacco and blown tobacco. The solid aerosol-forming substrate may be in bulk form or may be provided in a suitable container or cartridge. If desired, the solid aerosol-forming substrate may contain additional tobacco or non-tobacco volatile aroma compounds intended to be released upon heating of the substrate. The solid aerosol-forming substrate may also contain capsules that contain, for example, additional tobacco or non-tobacco volatile aroma compounds, and such capsules may melt during heating of the solid aerosol-forming substrate.

As used herein, the term "homogenized tobacco" refers to a material formed by agglomerating loose tobacco. The homogenized tobacco may be in the form of a sheet. The homogenized tobacco material may contain more than 5% by dry weight of aerosol forming agent. Alternatively, the homogenized tobacco material may contain from 5% to 30% by dry weight of aerosol forming agent. The sheets of homogenized tobacco material may be formed by agglomerating loose tobacco obtained by grinding or otherwise comminuting layers of tobacco leaf or ribs of tobacco leaf, or both. Alternatively or additionally, the sheets of homogenized tobacco material may comprise one or more of tobacco dust, tobacco fines, and other loose tobacco by-products generated, for example, during the processing, handling, and delivery of tobacco. The sheets of homogenized tobacco material may comprise one or more proprietary binders, i.e. tobacco endogenous binders, one or more external binders, i.e. tobacco exogenous binders, or a combination thereof, which promotes agglomeration of the bulk tobacco; alternatively or additionally, the sheets of homogenized tobacco material may contain other additives, including, but not limited to, tobacco and non-tobacco fibers, aerosol forming agents, humectants, plasticizers, flavoring agents, fillers, aqueous and non-aqueous solvents, and combinations thereof.

If necessary, the solid substrate forming the aerosol can be provided on or embedded in a thermally stable carrier. The carrier can be in the form of powder, granules, beads, grains, thin tubes, strips or sheets. Alternatively, the carrier can be a tubular carrier containing a thin layer of the solid substrate applied to its inner surface or to its outer surface, or to both its inner and outer surfaces. Such a tubular carrier can be made, for example, of paper or a paper-like material, a non-woven mat of carbon fibers, a lightweight metal mesh with open cells, or a perforated metal foil, or any other thermally stable polymer matrix.

The solid aerosol-forming substrate may be applied to the surface of the carrier in the form of, for example, a sheet, foam, gel or suspension. The solid aerosol-forming substrate may be applied to the entire surface of the carrier or, alternatively, may be applied in a pattern to provide non-uniform delivery of the fragrance during use.

The electrical circuit may be configured to detect the insertion and removal of the aerosol-forming substrate from the device. The electrical circuit may be configured to measure the initial electrical resistance of the heater upon initial insertion of the aerosol-forming substrate into the device, but before significant heating has occurred. The electrical circuit may compare the measured initial resistance with a range of acceptable electrical resistance stored in the memory device. If the initial resistance is outside the acceptable resistance, the aerosol-forming substrate may be considered counterfeit, incompatible, or damaged. In this case, the electrical circuit may be configured to prevent power supply until the aerosol-forming substrate is removed and replaced.

The electric heater may comprise one heating element. Alternatively, the electric heater may comprise more than one heating element, such as two, or three, or four, or five, or six, or more heating elements. The heating element or heating elements may be arranged in a suitable manner to most effectively heat the liquid substrate that forms the aerosol.

At least one electrical heating element preferably comprises an electrically resistive material. Suitable electrically resistive materials include, but are not limited to: semiconductors such as doped ceramics, electrically "conductive" ceramics (such as, for example, molybdenum disilicide), carbon, graphite, metals, metal alloys, and composite materials made of a ceramic material and a metallic material. Such composite materials may comprise doped or undoped ceramics. Examples of suitable doped ceramics include doped silicon carbides. Examples of suitable metals include titanium, zirconium, tantalum, and platinum group metals. Examples of suitable metallic alloys include stainless steel, constantan, nickel-, cobalt-, chromium-, aluminum-, titanium-, zirconium-, hafnium-, niobium-, molybdenum-, tantalum-, tungsten-, tin-, gallium-, manganese-, and iron-based alloys and nickel-, iron-, cobalt-based superalloys, stainless steel, Timetal®, iron-aluminum-based alloys, and iron-, manganese-, and aluminum-based alloys. Timetal® is a registered trademark of Titanium Metals Corporation. In composite materials, the electrically resistive material may be embedded in, encapsulated in, or coated with an insulating material, or vice versa, as appropriate, depending on the kinetics of energy transfer and the desired external physicochemical properties. The heating element may comprise an etched metal foil insulated between two layers of an inert material. In this case, the inert material may comprise Kapton®, all-polyimide or mica foil. Kapton® is a registered trademark of E.I. du Pont de Nemours and Company.

At least one electric heating element may have any suitable shape. For example, at least one electric heating element may have the shape of a heating plate. Alternatively, at least one electric heating element may have the shape of a box or substrate having different electrically conductive parts, or the shape of an electrically resistive metal tube. The liquid storage part may comprise a disposable heating element. Alternatively, one or more heating needles or rods that pass through the liquid substrate forming the aerosol may also be suitable. Alternatively, at least one electric heating element may comprise a flexible sheet of material. Other alternatives include a heating wire or thread, such as Ni-Cr (chromium-nickel), platinum, tungsten or alloy wire or a heating plate. Optionally, the heating element may be applied internally or externally to a rigid carrier material.

In one embodiment, the heating element comprises a grid, matrix, or woven material of electrically conductive threads. The electrically conductive threads may form voids between the threads, and the voids may have a width of 10 μm to 100 μm.

The electrically conductive threads may form a mesh of 160 to 600 US mesh (+/- 10%) (i.e., 160 to 600 threads per inch (+/- 10%)). The void width is preferably 75 μm to 25 μm. The percentage of open area of the mesh, which is the ratio of the void area to the total area of the mesh, is preferably 25 to 56%. The mesh may be formed using various types of woven or lattice structures. Alternatively, the electrically conductive threads consist of a matrix of threads arranged parallel to each other.

The electrically conductive threads may have a diameter of 10 μm to 100 μm, preferably 8 μm to 50 μm, and more preferably 8 μm to 39 μm. The threads may have a circular cross-section or may have a flattened cross-section.

The area of the grid, matrix or woven material of electrically conductive threads may be small, preferably less than or equal to 25 mm ² , allowing it to be incorporated into a hand-held system. The grid, matrix or woven material of electrically conductive threads may have, for example, a rectangular shape and dimensions of 5 mm by 2 mm. Preferably, the grid or matrix of electrically conductive threads occupies an area of 10% to 50% of the area of the heater assembly. More preferably, the grid or matrix of electrically conductive threads occupies an area of 15 to 25% of the area of the heater assembly.

The filaments may be formed by etching a sheet material such as foil. This may be particularly advantageous if the heater assembly comprises a matrix of parallel filaments. If the heating element comprises a mesh or woven fabric of filaments, the filaments may be produced individually and knitted together.

Preferred materials for conductive threads are stainless steel grades 304, 316, 304L and 316L.

At least one heating element may heat the liquid substrate forming the aerosol by conduction. The heating element may be at least partially in contact with the substrate. Alternatively, heat from the heating element may be conducted to the substrate by means of a heat-conducting element.

Preferably, during use, the aerosol-forming substrate is in contact with the heating element.

Preferably, the electrically controlled aerosol generating system further comprises a capillary material for transferring the liquid aerosol forming substrate from the liquid storage portion to the electric heating element.

Preferably, the capillary material is arranged to come into contact with the liquid in the liquid storage portion. Preferably, the capillary wick extends into the liquid storage portion. In this case, when used in the capillary wick, the liquid moves by capillary action from the liquid storage portion to the electric heater. In one embodiment, the capillary wick has a first end and a second end, wherein the first end extends into the liquid storage portion for contact with the liquid in it, and an electric heater is arranged at the second end with the possibility of heating the liquid. When the heater is activated, the liquid in the second end of the capillary wick evaporates under the action of at least one heating element of the heater to form a supersaturated vapor. The supersaturated vapor mixes with the air flow and moves in it. During the flow, the vapor condenses to form an aerosol, and the aerosol moves towards the user's mouth. The liquid substrate that forms the aerosol has physical properties, including viscosity and surface tension, that allow the liquid to be transported through the capillary wick by capillary action.

The capillary wick may have a fibrous or sponge structure. The capillary wick preferably comprises a bundle of capillaries. For example, the capillary wick may comprise several fibers or threads or other thin tubes. The fibers or threads may generally be aligned in the longitudinal direction of the aerosol generating system. Alternatively, the capillary wick may comprise a sponge-like or foam-like material that is formed in the form of a rod. The rod may extend along the longitudinal direction of the aerosol generating system. The wick structure forms several small channels or tubes through which liquid can be transported by capillary action. The capillary wick may comprise any suitable material or combination of materials. Examples of suitable materials are capillary materials, such as sponge or foam material, ceramic or graphite based materials in the form of fibers or sintered powders, foamed metal or plastic material, fibrous material, such as made of twisted or extruded fibers such as cellulose acetate, polyester, or bonded polyolefin, polyethylene, terylene or polypropylene fibers, nylon fibers or ceramics. The capillary wick may have any suitable capillarity and porosity so as to be used with liquids of different physical properties. The liquid has physical properties, including, but not limited to, viscosity, surface tension, density, thermal conductivity, boiling point and vapor pressure, which enable the liquid to be transported through the capillary device by capillary action.

The heating element may be in the form of a heating wire or thread that envelops and, optionally, supports the capillary wick. The capillary properties of the wick, combined with the properties of the liquid during normal use in the presence of a large amount of aerosol-forming substrate, ensure that the wick is always moist in the heating zone.

Alternatively, as described, the heating element may comprise a mesh formed from multiple electrically conductive filaments. The capillary material may extend into the voids between the filaments. The heater assembly may draw the liquid aerosol-forming substrate into the voids by capillary action.

The housing may comprise two or more different capillary materials, wherein the first capillary material, which is in contact with the heating element, has a higher thermal decomposition temperature, and the second capillary material, which is in contact with the first capillary material but not in contact with the heating element, has a lower thermal decomposition temperature. The first capillary material effectively acts as a separator separating the heating element from the second capillary material, so that the second capillary material is not exposed to temperatures exceeding its thermal decomposition temperature. In this context, "thermal decomposition temperature" means the temperature at which the material begins to decompose and lose mass as a result of the formation of gaseous products. The second capillary material may advantageously occupy a larger volume than the first capillary material and can retain a larger amount of aerosol-forming substrate than the first capillary material. The second capillary material may have better capillary properties than the first capillary material. The second capillary material may be less expensive or have a higher filling capacity than the first capillary material. The second capillary material may be polypropylene.

The power source may be any suitable power source, such as a DC voltage source. In one embodiment, the power source is a lithium-ion battery. Alternatively, the power source may be a nickel-metal hydride battery, a nickel-cadmium battery, or a lithium-based battery, such as a lithium-cobalt, lithium-iron phosphate, lithium-titanium, or lithium-polymer battery. Alternatively, the power source may be another type of charge storage device, such as a capacitor. The power source may require recharging and may have a capacity that allows storing enough energy for one or more aerosol generation sessions; for example, the power source may have sufficient capacity to allow continuous aerosol generation for approximately six minutes, which corresponds to the typical time spent smoking a conventional cigarette, or for a period that is a multiple of six minutes. In another example, the power source may have sufficient capacity to enable a specified number of puffs or individual heater activations.

Preferably, the aerosol generating system comprises a housing. Preferably, the housing is elongated. The housing may comprise any suitable material or combination of materials. Examples of suitable materials include metals, alloys, plastics or composite materials containing one or more of such materials, or thermoplastics suitable for use in the food or pharmaceutical industries, such as polypropylene, polyetheretherketone (PEEK) and polyethylene. Preferably, said material is lightweight and non-brittle.

Preferably, the electrically heated aerosol generating system is portable. The electrically heated aerosol generating system may have a size comparable to that of a conventional cigar or cigarette. The electrically heated aerosol generating system may have a total length of about 30 mm to about 150 mm. The electrically heated aerosol generating system may have an outer diameter of about 5 mm to about 30 mm.

The electrical circuit preferably comprises a microprocessor and more preferably a programmable microprocessor. The system may comprise a data input port or a wireless receiver allowing software to be loaded into the microprocessor. The electrical circuit may comprise additional electrical components. The system may comprise a temperature sensor.

If an adverse condition is detected, the system may only provide the user with an indication that an adverse condition has been detected. This may be done by means of a visual, audible or tactile warning. Alternatively or in addition, the electrical circuit may automatically limit or otherwise control the power supplied to the heater when an adverse condition is detected.

There are several ways in which the electrical circuit may be able to control the power supplied to the electric heater if an unfavorable condition is detected. If insufficient aerosol-forming substrate is delivered to the heating element, or the solid aerosol-forming substrate becomes dry, then it may be desirable to reduce or stop the power supply to the heater. This may be intended both to ensure that a suitable and pleasant sensation is provided to the user and to reduce the risks of overheating and the formation of undesirable compounds in the aerosol. The power supply to the heater may be stopped or limited. The power supply may be stopped or limited for a short period of time. However, preferably the power supply may be stopped or limited until the heater or aerosol-forming substrate is replaced.

For example, initially, 6 W pulses may be supplied to the heater during a puff. When an adverse condition is detected during a puff, the power supply may be limited to 5 W pulses for the remainder of the puff. In some embodiments, the electrical circuit may be configured to supply unlimited 6 W pulses to the heater during subsequent puffs until further adverse conditions are detected. However, in other preferred embodiments, the electrical circuit may be configured to supply limited 5 W pulses to the heater during subsequent puffs until the heater or the aerosol-forming substrate is replaced.

The system may comprise a puff detector for detecting the moment when the user takes a puff from the system, wherein the puff detector is connected to an electrical circuit, and wherein the electrical circuit is configured to supply power from the power supply to the heating element when the puff is detected by the puff detector, and wherein the electrical circuit is configured to determine the presence of an unfavourable condition during each puff.

The puff detector may be a dedicated puff detector that directly measures air flow through the device, such as a microphone-based puff detector, or may detect puffs indirectly, such as based on temperature changes in the device or changes in the electrical resistance of the heating element.

The electrical circuit may be configured to supply a specified power to the heating element during a time interval Δt ₁ after the initial detection of a puff or the initial supply of power to the heater, and the electrical circuit may be configured to determine a change in the electrical resistance of the heating element based on a measurement of the electrical resistance of the heating element at time t ₁ during each puff. The time interval Δt ₁ may be selected immediately after the initial detection of a puff or shortly after the first supply of power to the heater. This is especially advantageous during the first use after replacing the consumable cartridge, if the circuit detects an incompatible or counterfeit heater or aerosol-forming substrate. For example, a normal puff may have a duration of 3 s, and the response time of the puff detector may be approximately 100 ms. Then Δt ₁ may be selected in the range from 100 ms to 500 ms during the puff interval before the heater temperature stabilizes. Alternatively, the time interval Δt ₁ may be selected when the heating element temperature is expected to stabilize.

The electrical circuit may be configured to prevent the power supply to the heating element from the power supply unit if an unfavorable condition is determined for a predetermined number of consecutive or successive puffs by the user. The predetermined number of consecutive or successive puffs may be any suitable number. For example, the predetermined number of consecutive or successive puffs may be 1, 2, 3, 4, 5 or 6. Preferably, the predetermined number of consecutive or successive puffs is 3.

The electrical circuit may be configured to determine the presence of an adverse condition, limit or prevent power supply to the heater when the adverse condition is present, and continue to prevent or reduce power supply to the heating element until the adverse condition disappears.

In a liquid and wick system, over-tightening can cause the wick to dry out because the liquid cannot be replaced quickly enough near the heater. In these circumstances, it is advisable to limit the power supply to the heater to prevent the heater from becoming too hot and producing unwanted aerosol components. Once an unfavorable condition is detected, power to the heater can be cut off until the user takes another puff.

Similarly, over-tightening may not allow the heater to cool as expected between puffs, resulting in a gradual, undesirable increase in heater temperature from puff to puff. This is true for systems based on liquid or solid substrates that form an aerosol. In order to slow down the undesirable increase in heater temperature from puff to puff, when an unfavorable condition is detected, the electrical circuit may be configured to prevent or limit the supply of power during the remainder of the puff, and to continue to limit the supply of power to the heating element for subsequent puffs until the unfavorable condition disappears. The electrical circuit may be further configured to turn off the heating element or permanently or irreversibly prevent or block the supply of power to the heating element from the power supply if an unfavorable condition is detected for a predetermined number of consecutive or successive puffs by the user. As used herein, the term "turning off" refers to stopping the operation of the heating element. For example, the electrical circuit may be configured to cause a fuse connected to the heating element to blow if an unfavorable condition is determined for three consecutive puffs.

The electrical circuit may be configured to prevent power from being supplied to the heating element during a specified stop time interval when an adverse condition exists.

The electrical circuit may be configured to prevent power from being supplied to the heater until the consumable portion containing the aerosol-forming substrate or the heater is replaced.

Alternatively or in addition, the electrical circuit may be configured to calculate whether the difference between the initial resistance and the subsequent resistance has reached a maximum threshold value or a minimum threshold value, and compare the time taken for the difference to reach the threshold value with a stored time value, and determine the presence of an unfavorable condition and prevent or reduce the supply of power to the heater if the time taken to reach the threshold value is less than the stored time value, or if the difference does not reach the threshold value within the expected time interval. If the threshold value is reached faster than expected, this may indicate a dry heating element or dry substrate, or may indicate an incompatible, counterfeit or damaged heater. Similarly, if the threshold value is not reached within the expected time interval, this may indicate a counterfeit or damaged heater or substrate. This may provide the ability to quickly determine a counterfeit, damaged or incompatible heater or substrate.

In addition to indicating dry conditions on the heating element, the detection of an adverse condition may be an indication of a heater having electrical properties outside the range of expected properties. This may be due to the heater being faulty due to material buildup on the heater during its service life or due to it being an unauthorized or counterfeit heater. For example, if a manufacturer used stainless steel heating elements, these heating elements may be expected to have an initial electrical resistance at room temperature within a certain range of electrical resistance. In addition, the difference between the initial electrical resistance of the heater and the subsequent resistance of the heater may be expected to have a specific value as it relates to the material of the heating element. The electrical circuit may be configured to determine an adverse condition when the difference between the initial electrical resistance of the heater and the subsequent electrical resistance of the heater is outside the range of expected values and to limit or prevent power to the heater based on the result. This may prevent the use of certain unauthorized heaters.

Several different threshold values may be used to create different control strategies for different conditions. For example, a higher threshold value and a lower threshold value may be used to set boundaries for which the substrate heater must be replaced before further power is supplied. The circuit may be configured to prevent power from being supplied to the heater until either the heater or the aerosol-forming substrate is replaced if the difference is greater than the higher threshold value or less than the lower threshold value. One or more intermediate threshold values may be used to detect over-tightening behavior that results in dry conditions on the heater. The circuit may be configured to prevent power from being supplied to the heater for a certain time interval or until a subsequent user puff if the intermediate threshold value is exceeded but the higher threshold value is not exceeded. One or more intermediate threshold values may also be used to initiate an indication to the user that the aerosol-forming substrate is nearly depleted and will need to be replaced soon. The electrical circuit may be configured to provide an indication, which may be visible, audible, or tactile, if an intermediate threshold value is exceeded but the highest threshold value is not exceeded.

One method for detecting a counterfeit, damaged or incompatible heater is to check the resistance of the heater or the rate of change of the resistance of the heater when the heater is first used or inserted into the device or system. The electrical circuit can be configured to measure the initial resistance of the heating element for a predetermined time interval after power is applied to the heater. The predetermined time interval can be a short time interval and can be from 50 ms to 200 ms. For a heater containing a mesh heating element, the predetermined time interval can be approximately 100 ms. Preferably, the predetermined time interval is from 50 ms to 150 ms. The electrical circuit can be configured to measure the initial resistance of the heater as a separate procedure for applying power to the heater to heat the aerosol-forming substrate using significantly less power, or can measure the initial resistance of the heater during the first few moments when the heater is activated, before significant heating has occurred. The electrical circuit may be configured to compare the initial resistance of the heater with a range of acceptable values, and if the initial resistance is outside the range of acceptable values, the electrical circuit may be configured to prevent power from being supplied to the electric heater, or to provide an indication until the heater or aerosol-forming substrate is replaced.

If the initial resistance is within a range of acceptable values, the electrical circuit may be configured to determine the presence of an acceptable heater and control power supplied to the electric heater based on the presence of an acceptable heater or provide an indication in the absence of an acceptable heater.

The electrical circuit may be configured to determine the presence of an acceptable heater within one second of initially applying power to the heater.

According to a second aspect, there is provided a heater assembly for use in an electrically controlled aerosol generating system, such as the electrically controlled aerosol generating system according to the first aspect, or an electrically controlled aerosol generating device, wherein the heater assembly comprises:

an electric heater comprising at least one heating element; and

an electrical circuit connected to an electric heater and containing a storage device, wherein the electrical circuit is configured to:

measuring the initial electrical resistance of an electric heater;

measuring the subsequent electrical resistance of an electric heater after measuring the initial electrical resistance;

determining the difference between the initial electrical resistance and the subsequent electrical resistance;

determining when a determined difference between the subsequent electrical resistance and the initial electrical resistance of the electric heater is greater than a maximum threshold value or less than a minimum threshold value stored in the memory device; and

controlling the power supplied to the electric heater based on whether an unfavorable condition is detected or providing an indication when an unfavorable condition is detected.

The heater assembly may be configured to be used in an aerosol generating system and may be configured to heat an aerosol forming substrate during use.

According to a third aspect, there is provided an electrically controlled aerosol generating device for use in an electrically controlled aerosol generating system, such as the electrically controlled aerosol generating system according to the first aspect, wherein the electrically controlled aerosol generating device comprises:

power supply; and

an electrical circuit connected to a power supply and containing a storage device, wherein the electrical circuit is configured to:

connections to an electric heater of an electrically controlled aerosol generating system when in use;

measuring the initial electrical resistance of an electric heater;

measuring the subsequent electrical resistance of an electric heater after measuring the initial electrical resistance;

determining the difference between the initial electrical resistance and the subsequent electrical resistance;

determining the presence of an adverse condition when a determined difference between the subsequent electrical resistance and the initial electrical resistance is greater than a maximum threshold value or less than a minimum threshold value stored in the memory device; and

controlling the power supplied to the electric heater based on whether an unfavorable condition is determined to exist, or providing an indication if an unfavorable condition is determined to exist.

According to a fourth aspect of the present invention, there is provided an electrical circuit for an electrically controlled aerosol generating system, such as the electrically controlled aerosol generating system according to the first aspect, or an electrically controlled aerosol generating device, such as the electrically controlled aerosol generating device according to the third aspect, wherein in use the electrical circuit is connected to an electrical heater and a power supply, the electrical circuit comprises a memory device and is configured to:

measuring the initial electrical resistance of an electric heater and

measuring the subsequent electrical resistance of an electric heater after measuring the initial electrical resistance;

determining the difference between the initial electrical resistance and the subsequent electrical resistance;

determining an unfavourable condition when a determined difference between the subsequent electrical resistance and the initial electrical resistance is greater than a maximum threshold value or less than a minimum threshold value stored in a memory device; and

controlling the power supplied to the electric heater based on whether an unfavorable condition is determined to exist, or providing an indication if an unfavorable condition is determined to exist.

In use, the electrical circuit may be further connected to a puff detector to detect when the user takes a puff from the system, and the electrical circuit may be further configured to:

determining when an electrical circuit is connected to an electric heater;

measuring the initial resistance of an electric heater within a specified time interval after connecting the electrical circuit to the electric heater;

supplying power from the power supply to the heating element when a puff is detected by the puff detector;

measuring the subsequent resistance of the electric heater within a specified time interval after the start of power supply from the power supply to the electric heater;

determining the difference between subsequent resistance and initial resistance;

comparing the difference between the subsequent resistance and the initial resistance with at least one of a maximum threshold value and a minimum threshold value stored in the memory device;

determining the presence of an adverse condition if the difference is greater than a maximum threshold or less than a minimum threshold; and

limiting the power supplied to the electric heater during a puff if an adverse condition is determined to exist, or preventing power from being supplied to the electric heater for the remainder of the puff based on whether an adverse condition is determined to exist.

In some embodiments, the electrical circuit may be further configured to:

storing the result of determining an unfavorable condition in a storage device;

determining the number of consecutive adverse condition determination results based on the stored adverse condition determination results; and

disabling the cartridge if a certain number of consecutive adverse condition detection results are greater than the maximum threshold value.

The electrical circuit may be configured to disconnect the cartridge by any suitable means. For example, the electrical circuit may be configured to cause a fuse connected to the electric heater to blow.

According to a fifth aspect, a method is proposed for controlling the supply of power to an electric heater of an electrically controlled aerosol generating system, such as the electrically controlled aerosol generating system according to the first aspect, or an electrically controlled aerosol generating device, such as the electrically controlled aerosol generating device according to the third aspect, wherein the system or device comprises an electric heater comprising at least one heating element for heating an aerosol-forming substrate, and a power supply unit for supplying power to the electric heater, wherein the method comprises:

supplying power to the electric heater;

measurement of the initial electrical resistance of an electric heater;

measurement of the subsequent electrical resistance of an electric heater after measuring the initial electrical resistance;

determination of the difference between the initial electrical resistance and the subsequent electrical resistance;

determining an unfavourable condition when a specified difference between the subsequent electrical resistance and the initial electrical resistance is greater than a maximum threshold value or less than a minimum threshold value; and

controlling the power supplied to the electric heater based on whether an unfavorable condition is determined to exist, or providing an indication if an unfavorable condition is determined to exist.

The method may include measuring the initial electrical resistance of the heating element and measuring the electrical resistance of the heating element at a time after the initial supply of power to the electric heater from the power supply.

The method may include supplying a constant power to the heater when power is applied. Alternatively, variable power may be supplied depending on other operating parameters. In this case, the threshold may depend on the power supplied to the heater.

The method may include determining the initial electrical resistance before the first use of the heater. If the initial resistance is determined before the first use of the heater, it can be assumed that the heating element is at approximately room temperature. Since the expected change in resistance over time may depend on the initial temperature of the heating element, measuring the initial resistance at or near room temperature allows for narrower ranges of expected behavior.

The method may include calculating the initial resistance as the measured initial resistance minus an estimated parasitic resistance due to the presence of other electrical components and electrical contacts within the system.

An electrically controlled aerosol generating system may comprise a puff detector for detecting when a user takes a puff from the system, and the method may include supplying power from a power supply to a heating element when a puff is detected by the puff detector, determining the presence of an adverse condition during each puff, and preventing the power supply from supplying power to the heating element from the power supply when an adverse condition is present for a specified number of consecutive puffs by the user.

The method may include preventing power from being supplied to the heating element from the power supply when an unfavorable condition exists.

The method may include continuously determining the presence of an adverse condition, preventing power from being supplied to the heater when the adverse condition is present, and continuing to prevent power from being supplied to the heating element until the adverse condition disappears.

The method may include preventing power from being supplied to the heating element during a specified stop time interval when an unfavorable condition exists.

Alternatively or additionally, the method may include continuously calculating whether the difference has exceeded a maximum threshold value or a minimum threshold value, and comparing the time required to reach the threshold value with a stored time value, and if the time required to reach the threshold value is less than the stored time value, determining an unfavorable condition and controlling the supply of power to the heater.

In some embodiments, the electrically controlled aerosol generating system may further comprise a removable cartridge and a device configured to receive the removable cartridge therein with the ability to remove it, wherein the removable cartridge comprises an electric heater and a liquid substrate that forms the aerosol, and the device comprises a power supply unit and an electrical circuit, wherein the electrical circuit is connected to a puff detector for detecting the moment when the user takes a puff from the system. In these embodiments, the method may further comprise:

measuring the initial resistance of the electric heater before the puff is detected by the puff detector;

supplying power from the power supply to the heating element when a puff is detected by the puff detector;

measuring the subsequent resistance of the electric heater within a specified time interval after the start of power supply from the power supply to the electric heater;

determining the difference between subsequent resistance and initial resistance;

comparing the difference between the subsequent resistance and the initial resistance with at least one of a maximum threshold value and a minimum threshold value stored in the memory device;

determining the presence of an adverse condition if the difference is greater than a maximum threshold or less than a minimum threshold; and

limiting the power supplied to the electric heater during the puff if an adverse condition is determined to exist, or preventing power from being supplied to the electric heater during the remainder of the puff if an adverse condition is determined to exist.

In some embodiments, the method further comprises:

determining when an electrical circuit is connected to an electric heater; and

measuring the initial resistance of an electric heater within a specified time interval after connection to the electric heater.

According to a sixth aspect of the present invention, there is provided a method for detecting an incompatible or damaged heater of an electrically controlled aerosol generating system, such as the electrically controlled aerosol generating system of the first aspect, or an electrically controlled aerosol generating device, such as the electrically controlled aerosol generating device of the third aspect, wherein the system or device comprises an electric heater comprising at least one heating element for heating an aerosol-forming substrate, and a power supply for supplying power to the electric heater, wherein the method comprises:

supplying power to the electric heater;

measurement of the initial electrical resistance of an electric heater;

measurement of the subsequent electrical resistance of an electric heater after measuring the initial electrical resistance;

determination of the difference between the initial electrical resistance and the subsequent electrical resistance;

determining an incompatible or damaged heater when a determined difference between the subsequent electrical resistance and the initial electrical resistance is greater than a maximum threshold value or less than a minimum threshold value, or when the difference reaches a threshold value stored in a memory device outside an expected time interval.

The method may include preventing power from being supplied to the electric heater or providing an indication until the heater or aerosol-forming substrate is replaced if the heater is determined to be an incompatible heater.

The method may further include measuring the initial resistance of the heater or the initial rate of change of the resistance of the heater during a specified time interval after power is supplied to the heater, comparing the initial resistance of the heater or the initial rate of change of the resistance of the heater with a range of acceptable values, and if the initial resistance or the initial rate of change of the resistance is outside the range of acceptable values, then preventing power from being supplied to the electric heater or providing an indication until the heater or the aerosol-forming substrate is replaced.

The predetermined time interval may be a short time interval and may be from 50 ms to 200 ms. For a heater comprising a mesh heating element, the predetermined time interval may be approximately 100 ms. Preferably, the predetermined time interval is from 50 ms to 150 ms.

Determining the initial rate of change of resistance during a given time interval can be achieved by obtaining several resistance measurement results at different times during a given time interval and calculating the rate of change of resistance based on the several resistance measurement results.

The method may further include detecting the moment when the heater or the aerosol-forming substrate is inserted into the system. The method may be performed immediately after detecting that the heater or the aerosol-forming substrate has been inserted into the system.

According to a seventh aspect of the present invention, a computer program product is proposed, directly loaded into the internal memory of a microprocessor containing parts of the software code for performing the steps according to the fifth or sixth aspect, when said product is launched on the microprocessor in an electrically controlled aerosol-generating system, wherein the system comprises an electric heater containing at least one heating element for heating an aerosol-forming substrate, and a power supply for supplying power to the electric heater, wherein the microprocessor is connected to the electric heater and the power supply.

The computer software product may be provided as a downloadable piece of software or recorded on a machine-readable storage medium.

According to an eighth aspect, a machine-readable storage medium is provided on which a computer program according to the seventh aspect is stored.

The features described with respect to one aspect of the invention may be applied to other aspects of the present invention. In particular, the features described with respect to the first aspect may be applied to the second, third and fourth aspects of the present invention. The features described with respect to the first, second, third and fourth aspects of the present invention may also be applied to the fifth, sixth and seventh aspects of the present invention.

The present invention will now be described by way of example only, with reference to the accompanying graphic materials, where:

Fig. 1a-1d show schematic illustrations of a system according to an embodiment of the present invention;

Fig. 2 shows an exploded view of a cartridge for use in the system shown in Fig. 1a-1d;

Fig. 3 shows a detailed view of the heater filaments, showing the meniscus of the liquid substrate forming the aerosol between the filaments;

Fig. 4 shows a schematic illustration of the change in heater resistance during a user's puff;

Fig. 5 shows an electrical circuit diagram showing how the resistance of a heating element can be measured;

Fig. 6 shows a control method after detecting an unfavorable condition;

Fig. 7 shows a schematic illustration of a first alternative aerosol generating system;

Fig. 8 shows a schematic illustration of a second alternative aerosol generating system; and

Fig. 9 is a block diagram illustrating a method for detecting an unauthorized, damaged, or incompatible heater.

Fig. 1a-1d are schematic illustrations of an electrically heated aerosol generating system comprising a cartridge according to an embodiment of the present invention. Fig. 1a is a schematic view of an aerosol generating device 10 and a separate cartridge 20, which together form an electrically heated aerosol generating system.

The cartridge 20 contains an aerosol-forming substrate and is designed to be placed in a cavity 18 inside the device. The cartridge 20 must be designed to be replaceable by the user if the aerosol-forming substrate provided in the cartridge is exhausted. Fig. 1a shows the cartridge 20 immediately before insertion into the device, wherein the arrow 1 shown in Fig. 1a indicates the direction of insertion of the cartridge.

The aerosol generating device 10 is portable and has a size comparable to the size of a traditional cigar or cigarette. The device 10 comprises a main part 11 and a mouthpiece part 12. The main part 11 contains a battery 14, such as a lithium iron phosphate battery, an electrical circuit 16 and a cavity 18. The electrical circuit 16 contains a programmable microprocessor. The mouthpiece part 12 is connected to the main part 11 by means of a hinge joint 21 and can move between an open position, as shown in Fig. 1, and a closed position, as shown in Fig. 1d. The mouthpiece part 12 is positioned in an open position to allow insertion and removal of cartridges 20, and is positioned in a closed position when the system is to be used for generating an aerosol. The mouthpiece portion comprises a plurality of air inlet openings 13 and an outlet opening 15. In use, the user draws on the outlet opening side to draw air through the air inlet openings 13 through the mouthpiece portion into the outlet opening 15 and subsequently into the user's mouth or lungs. Internal partitions 17 are provided to force air to flow through the mouthpiece portion 12 past the cartridge.

The cavity 18 has a circular cross-section and is sized to accommodate the housing 24 of the cartridge 20. Electrical connectors 19 are provided on the sides of the cavity 18 to provide an electrical connection between the control electronics 16 and the battery 14 and the corresponding electrical contacts on the cartridge 20.

Fig. 1b shows the system shown in Fig. 1a with a cartridge inserted into cavity 18 and the covering 26 removed. In this position, the electrical connectors are pressed against the electrical contacts on the cartridge.

Fig. 1c shows the system shown in Fig. 1b, with the covering 26 completely removed and the mouthpiece portion 12 moved to the closed position.

Fig. 1d shows the system shown in Fig. 1c with the mouthpiece portion 12 in a closed position. The mouthpiece portion 12 is held in the closed position by a locking mechanism. The mouthpiece portion 12 in the closed position holds the cartridge in electrical contact with the electrical connectors 19 in such a way that a good electrical connection is maintained during use regardless of the orientation of the system.

Fig. 2 shows an exploded view of the cartridge 20. The cartridge 20 includes a generally circular cylindrical body 24 that has a size and shape selected for placement in the cavity 18. The body includes a capillary material 27, 28 that is impregnated with a liquid substrate that forms an aerosol. In this example, the aerosol-forming substrate contains 39% by weight of glycerin, 39% by weight of propylene glycol, 20% by weight of water and flavorings, and 2% by weight of nicotine. The capillary material is a material that actively transfers liquid from one end to the other and can be made of any suitable material. In this example, the capillary material is formed from polyester.

The housing has an open end to which a heater assembly 30 is attached. The heater assembly 30 comprises a substrate 34 having an opening 35 formed therein, a pair of electrical contacts 32 attached to the substrate and separated from each other by a gap 33, and a plurality of electrically conductive heater threads 36 filling the opening and attached to electrical contacts on opposite sides of the opening 35.

The heater assembly 30 is covered with a removable cover 26. The cover comprises a liquid-impermeable plastic sheet which is adhered to the heater assembly but which can be easily removed. A projection is provided on the side of the cover to allow the user to grasp the cover when removing it. It will now be apparent to a person skilled in the art that, although gluing is described as a method for attaching the impermeable plastic sheet to the heater assembly, other methods known to those skilled in the art may be used, including heat welding or ultrasonic welding, provided that the cover can be easily removed by the user.

The cartridge of Fig. 2 comprises two separate capillary materials 27, 28. A disk of the first capillary material 27 is provided for contact with the heating element 36, 32 in use. A large part of the second capillary material 28 is provided on the opposite side of the first capillary material 27 relative to the heater assembly. Both the first capillary material and the second capillary material retain the liquid substrate that forms the aerosol. The first capillary material 27, which is in contact with the heating element, has a higher thermal decomposition temperature (at least 160 °C or higher, such as approximately 250 °C) than the second capillary material 28. The first capillary material 27 effectively acts as a separator separating the heating element 36, 32 from the second capillary material 28, so that the second capillary material is not exposed to temperatures exceeding its thermal decomposition temperature. The temperature difference in the first capillary material is such that the second capillary material is exposed to temperatures below its thermal decomposition temperature. The second capillary material 28 can be selected so as to have better capillary properties than the first capillary material 27, to have the ability to hold more liquid per unit volume than the first capillary material, and to be less expensive than the first capillary material. In this example, the first capillary material is a heat-resistant material such as fiberglass or a material containing fiberglass, and the second capillary material is a polymer such as a suitable capillary material. Examples of suitable capillary materials include the capillary materials discussed herein, and in alternative embodiments can include high-density polyethylene (HDPE) or polyethylene terephthalate (PET).

The capillary material 27, 28 is preferably oriented in the housing 24 in such a way as to transfer liquid to the heater assembly 30. When the cartridge is assembled, the heater threads 36, 37, 38 can be in contact with the capillary material 27, and therefore the aerosol-forming substrate can be directly transferred to the mesh heater. Fig. 3 shows a detailed view of the heater threads 36 in the assembly, which shows a meniscus 40 of the liquid aerosol-forming substrate between the heater threads 36. As shown, the aerosol-forming substrate is in contact with most of the surface of each thread, so that most of the heat generated by the heater assembly passes directly into the aerosol-forming substrate.

Thus, during normal operation, the liquid substrate that forms the aerosol contacts a large portion of the surface of the filaments 36 of the heater. However, when most of the liquid substrate in the cartridge has been used up, less liquid substrate that forms the aerosol will be delivered to the filaments of the heater. With less liquid to evaporate, less energy is absorbed by the enthalpy of evaporation, and more of the energy supplied to the filaments of the heater is directed to increasing the temperature of the heating filaments. As the heating element dries out, the rate of increase in temperature of the heating element for a given supplied power will increase. The heating element may dry out because the aerosol-forming substrate in the cartridge is almost used up, or because the user takes very long or very frequent puffs, and the liquid cannot be delivered to the filaments of the heater as quickly as it evaporates.

In use, the heater assembly operates by resistive heating. Current is passed through the filaments 36 under the control of the control electronics 16 to heat the filaments to a desired temperature range. The grid or matrix of filaments has a significantly higher electrical resistance than the electrical contacts 32 and the electrical connectors 19, so that high temperatures are localized on the filaments. In this example, the system is configured to generate heat by supplying an electrical current to the heater assembly in response to a user's puff. In another embodiment, the system can be configured to continuously generate heat when the device is in the "on" state. Different filament materials may be suitable for different systems. For example, in a continuous heating system, Ni-Cr filaments are suitable because they have a relatively low specific heat capacity and are compatible with low current heating. In a puff-activated system where heat is generated in short bursts using high current pulses, stainless steel filaments having a high specific heat capacity may be more suitable.

The system comprises a puff sensor configured to detect the moment when the user draws air through the mouthpiece. The puff sensor (not shown) is connected to the control electronics 16, and the control electronics 16 are configured to supply current to the heater assembly 30 only when it is determined that the user is drawing from the device. Any suitable air flow sensor can be used as a puff sensor, such as a microphone or a pressure sensor.

In order to detect this increase in the rate of temperature change, the electrical circuit 16 is configured to measure the electrical resistance of the heater filaments. The heater filaments in this example are made of stainless steel and have a positive temperature coefficient of resistance. This means that as the temperature of the heater filaments increases, their electrical resistance increases. It should be understood that in other embodiments, the heater filaments may be made of a material having a negative coefficient of resistance, as a result of which, as the temperature of the heater filaments increases, their electrical resistance decreases.

Fig. 4 shows a schematic illustration of the change in resistance of the heater during a user puff. The x-axis represents the time after the initial detection of the user's puff and the resulting application of power to the heater. The y-axis represents the electrical resistance of the heater assembly. It can be seen that the heater assembly has an initial resistance of R ₁ before any heating occurs. R ₁ consists of a parasitic resistance R _P caused by the electrical contacts 32 and the electrical connectors 19 and the contact between them, and the resistance of the heater filaments R ₀ . When power is applied to the heater during a user's puff, the temperature of the heating filaments increases and therefore the electrical resistance of the heating filaments increases. As shown, at time t ₁ , after a time interval of Δt ₁ has passed from 1 application of power to the heater from the power supply, the resistance of the heater assembly is R ₂ . Thus, the change in the electrical resistance of the heater assembly from the initial resistance to the resistance at time t ₁ is ΔR = R ₂ - R ₁ .

In this example, it is assumed that the parasitic resistance R _P does not change when the heater filaments are heated. This is because R _P is due to unheated components such as electrical contacts 32 and electrical connectors 19. The value of R _P is assumed to be the same for all cartridges and the value is stored in the circuit memory.

In order to detect a rapid increase in the temperature of the heater filaments, indicating a dry condition on the heater filaments, it is possible to monitor a change in the resistance of the heater filaments. The electrical circuit may be configured to determine the change in resistance by determining the difference between the results of measuring the initial electrical resistance R ₁ of the heater filaments before power is supplied to the heating elements, in other words, before tightening, and the results of measuring the electrical resistance R ₂ of the heater filaments after a predetermined time interval Δt ₁ has passed, after which power is supplied to the heater filaments. In addition, the electrical circuit may be configured to determine whether the change in resistance is an indication of an unacceptably rapid increase in temperature, by comparing the difference ΔR with a predetermined maximum threshold value ΔR _max .

R ₂ and R ₁ are the measured values, and ΔR _max is stored in the memory. Ideally, the value of R ₁ is measured before heating occurs, in other words, before the heater is first activated. This initial measured value can be used for all subsequent puffs to avoid any error due to residual heat from previous puffs. The initial measured electrical resistance before heating is therefore referred to as R _1ref .

R _1ref may be measured only once for each cartridge, and a detection system is used to determine when a new cartridge is inserted, or R ₁ may be measured each time the system is turned on. However, preferably, the electrical circuit is configured to periodically obtain updated R _1ref measurements after predetermined time intervals have passed during which no power is supplied to the heater filaments. The predetermined time interval is typically 3 minutes, but may be any suitable period of time required for the heater filaments to cool from their operating temperature back to room temperature. Periodic updates of R _1ref may provide for recalibration of the electrical circuit to compensate for changes in ambient air temperature and changes in the state of the heater filaments.

In this example, software running on a microprocessor in an electrical circuit performs the following comparison to determine whether an unfavorable condition exists:

If R ₂ >R _lref +ΔR _max , then the heater is in a dry state (1)

In a similar manner, other unfavorable conditions can be detected, in addition to the dry state of the heater. For example, if a cartridge containing a heater made of a material having a different temperature coefficient of resistance is used in the system, the electrical circuit can detect this and can be configured to not supply power to it. In the present example, the heater filaments are made of stainless steel. A cartridge containing a heater made of Ni-Cr will have a lower temperature coefficient of resistance, which means that its resistance will increase more slowly with increasing temperature. Thus, a minimum threshold resistance value ΔR _min can be stored in the memory of the electrical circuit, which corresponds to the slowest increase in temperature in the time interval Δt ₁ expected for a heating element made of stainless steel. The electrical circuit can be configured to determine the unfavorable condition corresponding to an unauthorized cartridge located in the system if the change in resistance between R ₂ and R _1ref is less than the minimum threshold value ΔR _min .

Thus, the system may be configured to compare the difference between R ₂ and R _1ref with a stored upper threshold value and a stored lower threshold value to determine unfavorable conditions. R _1ref may also be compared with a threshold value or thresholds to verify that it is within the expected range. There may even be more than one stored upper threshold value, with different actions taken depending on which upper threshold value is exceeded. For example, if the highest threshold value is exceeded, the circuit may prevent further power supply until the heater and/or substrate are replaced. This may indicate complete depletion of the substrate, or a damaged or incompatible heater. The lower threshold value may be used to determine when the substrate is almost depleted. If this lower threshold value is exceeded, but the upper threshold value is not exceeded, then the circuit may simply provide an indication, such as an illuminated LED, indicating that the substrate will soon need to be replaced.

The difference between R _1ref and R ₂ can be continuously monitored to determine whether the heater is cooling sufficiently between puffs. If the difference does not fall below the cooling threshold between puffs because the user is puffing very frequently, the circuitry can prevent or limit power to the heater until the difference falls below the cooling threshold. Alternatively, a comparison can be made between the maximum value of the difference during a puff and the minimum value for the difference after a puff to determine whether sufficient cooling is occurring.

In addition, the difference between R ₁ and R ₂ can be continuously monitored and the time at which it reaches the threshold compared to a temporary threshold. If the difference between R _1ref and R ₂ reaches the threshold much faster or slower than expected, this may indicate an unfavorable condition, such as an incompatible heater. The rate of change can also be determined and compared to a threshold. If the difference increases very quickly or very slowly, this may indicate an unfavorable condition. These techniques can provide the ability to very quickly detect incompatible heaters.

Fig. 5 shows a circuit diagram showing how the resistance of a heating element can be measured. In Fig. 5, a heater 501 is connected to a battery 503 which provides a voltage V2. R _heater is the resistance of the heater which is to be measured at a certain time. In series with the heater 501 between ground and the voltage V2, an additional resistor 505 with a known resistance r is connected to the voltage V1. In order for the microprocessor 507 to measure the resistance of the heater 501, both the current through the heater 501 and the voltage across the heater 501 can be determined. Then, the following well-known formula can be used to determine the resistance:

In Fig. 5 the voltage across the heater is V2-V1, and the current through the heater is I. Thus:

The additional resistor 505, whose resistance r is known, is used to determine the current I, again using equation (2) above. The current through resistor 505 is I, and the voltage across resistor 505 is V1. Thus:

So, combining (5) and (6) gives:

Thus, the microprocessor 507 can measure V2 and V1 as the aerosol generating system is used and, knowing the value of r, can determine the heater resistance R _heater at different points in time.

The circuitry may control the supply of power to the heater in several different ways after an adverse condition has been detected. Alternatively or in addition, the circuitry may simply provide an indication to the user that an adverse condition has been detected. The system may include an LED or a display or may include a microphone, and these components may be used to provide a warning to the user of an adverse condition.

Fig. 6 shows a control method for a puff-activated system according to the present invention. Fig. 6 shows four successive puffs, P ₁ , P ₂ , P ₃ and P ₄ . The first puff P ₁ is a normal puff in which there is no abnormal condition. All three subsequent puffs P ₂ , P ₃ and P ₄ are abnormal puffs that exceed the upper threshold value ΔR _max .

Each puff is detected at time _t1 , at which time power is applied to the heater filaments. The resistance of the heater filaments at time _t1 is shown as _R1 . The initial resistance _R1 of the heater filaments for the first puff P1 is equal to the initial reference resistance _R1ref , which was measured before heating began. Subsequent anomalous puffs _P2 , _P3 , and _P4 exhibit an initial resistance _R1 at time _t1 that is higher than the initial reference resistance _R1ref . This indicates that the heater filaments have not had sufficient time to cool back to room temperature between puffs. The resistance of the heater filaments is measured at time _t2 , after a specified time interval _Δt1 has passed since the puff was detected. Each puff ends at time _t3 and lasts for a total time interval _Δtpuff .

In the control method of Fig. 6, the electrical circuit stops supplying power to the heater as soon as it is determined that the upper threshold value has been exceeded, until the user has finished puffing. This is shown at time t _h for the second, third and fourth puffs P ₂ , P ₃ and P ₄ . This can be useful to prevent the heater from becoming too hot, even if the user puffs too hard. In addition to stopping the power supply, an indication can be provided that the threshold value has been reached.

When a new puff from the user is detected, power is again supplied to the heater. This is shown for puffs P ₃ and P ₄ . A single instance of exceeding the upper threshold may result from a very long puff by the user, but multiple consecutive puffs during which the upper threshold is exceeded are more likely to result from the cartridge becoming empty. Thus, in this example, if ΔR exceeds the upper threshold ΔR _max for a specified number of consecutive puffs, typically 3 puffs, the cartridge is disabled by causing the fuse in the cartridge to blow. It should be understood that the cartridge may be disabled in other ways, for example, the electrical circuit may block additional power to the heater filaments until the cartridge is replaced or refilled, or until the user performs a reset operation.

In most embodiments, cartridges can be removed from devices. A user can remove a cartridge from a device when the cartridge has run out of aerosol-forming liquid substrate to dispose of or refill the cartridge. A user can also remove a cartridge that is partially empty and still contains aerosol-forming liquid substrate.

The user may insert a used cartridge into the device. For example, the user may insert a refilled or partially empty cartridge into the device. When the user inserts a recently used cartridge into the device, the heater may not have had enough time to cool to room temperature after previous use. If the device's electrical circuit measures the initial resistance R _1ref of the heater filaments when the heater filaments are still hot, this may distort the electrical circuit's determination of adverse conditions and may also cause the heater filaments to heat up to an undesirable temperature.

Thus, the electrical circuit may be configured to determine whether the temperature of the heater of the newly inserted cartridge is stable. In other words, the electrical circuit may be configured to determine whether the heater of the newly inserted cartridge has a reduced temperature, typically room temperature. This may substantially prevent or inhibit the electrical circuit from measuring the initial resistance R _1ref of the heater filaments when the heater filaments are hot.

In most embodiments, the electrical circuit is configured to determine when the cartridge is placed in the device. Thus, the electrical circuit is configured to determine when the cartridge is removed from the device and when the cartridge is inserted into the device.

When the electrical circuit determines that the cartridge is inserted into the device, the electrical circuit may be configured to measure the preliminary resistance R _P1 of the heater filaments. The electrical circuit may also be configured to measure the subsequent preliminary resistance R _P2 of the heater filaments after a specified time interval ΔT ₂ has passed, typically from approximately 1 s to approximately 2 s.

In this case, the electrical circuit can be configured to determine the difference ΔR _P between the measured preliminary resistances R _P1 , R _P2 . If the temperature of the heater filaments is stable, the difference in values |ΔR _P | should be small or zero. However, if the value of the difference |ΔR _P | is relatively large, this indicates that the temperature of the heater filaments is not stable. If the difference |ΔR _p | is relatively large, this indicates that the heater filaments are hot and are cooling down over a time interval ΔT ₂ . The electrical circuit can be configured to compare the difference ΔR _P with a minimum threshold value ΔR _pmin and determine whether the temperature of the heater filaments is stable, based on the comparison. The electrical circuit can be configured to determine that the temperature of the heater filaments is not stable if the difference |ΔR _p | is greater than the minimum threshold value ΔR _pmin . The electrical circuit can be configured to perform the following comparison:

If |R _p2 -R _p1 |>ΔR _pmin , then the heater temperature is not stable, (6),

where R _p2 and R _pl are the measured values, and ΔR _pmin is stored in the memory device.

It should also be understood that in some embodiments, the electrical circuit may be configured to compare the magnitude of the difference |ΔR _p | with a minimum threshold value ΔR _pmin . The electrical circuit may be configured to determine that the temperature of the heater filaments is not stable if the magnitude of the difference |ΔR _p | is greater than the minimum threshold value ΔR _pmin .

If the electrical circuit determines that the temperature of the heater filaments is not stable, the electrical circuit may prevent power from being supplied to the heater filaments and may not measure and store the initial resistance R _lref . The electrical circuit may be configured to periodically or continuously measure the subsequent preliminary resistance R _p2 , determine the difference ΔR _p with the initial preliminary resistance R _pl and compare the difference ΔR _p with a minimum threshold value ΔR _pmin until the difference is at an expected level for the heater filaments at a stable temperature that is as close to zero as possible.

If the electrical circuit determines that the temperature of the heater filaments is stable, the electrical circuit may be configured to determine the initial reference resistance R _1ref and perform the normal processes described above.

It should also be understood that in some embodiments, the electrical circuit may be configured to periodically measure one preliminary resistance R _pl after inserting a new cartridge and determine the difference ΔRp between the preliminary resistance R _pl and the previous reference resistance R _1ref , which was measured and stored for the previous cartridge, before removing the previous cartridge.

Although the present invention has been described with reference to a system based on a cartridge with a mesh heater, the same methods for detecting adverse conditions can be used in other aerosol generating systems.

In Fig. 7 an alternative system is illustrated which also uses a liquid substrate and a capillary material in accordance with the present invention. The electrically heated aerosol generating system 100 shown in Fig. 7 comprises a housing 101 having a mouthpiece end 103 and a main part end 105. At the end of the main part an electrical power supply unit is provided in the form of a battery 107 and an electrical circuit 109. Together with the electrical circuit 109 a puff detection system 111 is also provided. At the mouthpiece end a liquid storage portion is provided in the form of a cartridge 113 containing liquid 115, a capillary wick 117 and a heater 119. It should be noted that in Fig. 7 the heater is shown only schematically. One end of the capillary wick 117 passes into the cartridge 113, and the other end of the capillary wick 117 is surrounded by a heater 119. The heater is connected to the electrical circuit by means of connections 121, which can pass along the outside of the cartridge 113 (not shown in Fig. 7). The housing 101 also contains an inlet 123 for air, an outlet 125 for air at the mouthpiece end and a chamber 127 for forming an aerosol.

In use, the operation is as follows. Liquid 115 is transferred by capillary action from the cartridge 113 from the end of the wick 117 that extends into the cartridge to the other end of the wick, which is surrounded by a heater 119. When the user puffs through the aerosol generating system at the air outlet 125, ambient air is drawn in through the air inlet 123. In the arrangement shown in Fig. 7, the puff detection system 111 detects a puff and activates the heater 119. The battery 107 supplies electrical energy to the heater 119 to heat the end of the wick 117 surrounded by the heater. The liquid at this end of the wick 117 is vaporized by the heater 119 to create a supersaturated vapor. At the same time, the evaporated liquid is replaced by another liquid moving along the wick 117 due to capillary action. The resulting supersaturated vapor mixes with the air flow and moves in it from the air inlet 123. In the aerosol formation chamber 127, the vapor condenses to form an inhalable aerosol, which is transferred to the outlet 125 and into the user's mouth.

In the embodiment shown in Fig. 7, the electrical circuit 109 and the puff detection system 111 are programmable, as in the embodiment shown in Fig. 1a-1d.

The capillary wick may be made of various porous or capillary materials and preferably has a known specified capillarity. Examples include ceramic or graphite based materials in the form of fibers or sintered powders. Wicks of different porosities may be used to match different physical properties of the liquid, such as density, viscosity, surface tension and vapor pressure. The wick must be suitable so that the required amount of liquid can be delivered to the heater when the liquid storage portion contains enough liquid.

The heater comprises at least one heating wire or filament passing around the capillary wick.

As in the system described with reference to Fig. 1-3, the capillary material forming the wick may dry out near the heating wire if the liquid in the cartridge is used up or if the user takes very long deep puffs. In the same manner as described with reference to the system of Fig. 1-3, the change in the resistance of the heating wire during the first part of each puff may be used to determine the presence of an unfavorable condition, such as a dry wick.

A system of the type illustrated in Fig. 7 may have significant differences in heater resistance, even between cartridges of the same type, due to differences in the length of the heating wire wrapped around the wick. The present invention is particularly advantageous because it does not require the electrical circuit to maintain a maximum heater resistance value as a threshold; instead, an increase in resistance relative to the initial measured resistance is used.

Fig. 8 illustrates another aerosol generating system that can implement the present invention. The embodiment of Fig. 8 is an electrically heated tobacco device that heats, but does not combust, a solid tobacco-based substrate to produce an aerosol for inhalation. In Fig. 8, the components of the aerosol generating device 700 are shown in a simplified manner and are not drawn to scale. Elements that are not essential to understanding the embodiment have been omitted to simplify Fig. 8.

An electrically heated aerosol generating device 200 comprises a housing 203 and a substrate 210 that generates an aerosol, such as a cigarette. The aerosol generating substrate 210 is pushed into a cavity 205 formed by the housing 203 to thermally contact the heater 201. The aerosol generating substrate 210 releases a number of volatile compounds at different temperatures. By controlling the operating temperature of the electrically heated aerosol generating device 200 so that it is lower than the release temperature of some of the volatile compounds, it is possible to avoid the release or formation of smoke constituents.

Inside the housing 203 there is an electrical power supply unit 207, for example, a rechargeable lithium-ion battery. An electrical circuit 209 is connected to the heater 201 and the electrical power supply unit 207. The electrical circuit 209 controls the power supplied to the heater 201 to regulate its temperature. The aerosol formation detector 213 can detect the presence and identity of the aerosol-forming substrate 210 in thermal contact with the heater 201 and signals the presence of the aerosol-forming substrate 210 to the electrical circuit 209. Provision of the substrate detector is optional. An air flow sensor 211 is provided inside the housing and is connected to the electrical circuit 209 to determine the air flow rate through the device.

In the embodiment described, the heater 201 is an electrically resistive track or tracks applied to a ceramic substrate. The ceramic substrate is in the form of a plate and is inserted into the aerosol-forming substrate 210 during use. The heater is part of the device and can be used to heat many different substrates. However, the heater can be a replaceable component, and replaceable heaters can have different electrical resistances.

A system of the type described in Fig. 8 may be a continuous heating system in which the heater temperature is maintained at a target temperature while the system is on, or it may be a puff activated system with the heater temperature increased by supplying more power at intervals when a puff is detected.

In the case of a puff-activated system, its operation is very similar to that described with reference to the previous embodiments. If the substrate is dry in the immediate vicinity of the heater, the resistance of the heater will increase faster for a given applied power than if the substrate still contained aerosol-forming substances that can evaporate at a relatively low temperature.

In the case of a continuous heating system, the temperature of the heater initially drops when the user takes a puff from the system due to the cooling effect of the air flow passing through the heater. The resistance of the heater can be measured when the puff is first detected and recorded as R ₁ , and the subsequent resistance R ₂ , when the system returns the heater back to the target temperature, can be measured after a time interval Δt ₁ has passed after the puff is detected, in the same manner as described. ΔR can then be calculated as described above and compared with the stored threshold value as described above to determine whether the substrate is dry near the heater. The substrate may be dry because it has been exhausted by use, or because it is old or improperly stored, or because it is counterfeit and has a moisture content that differs from the genuine aerosol-forming substrate.

The system in Fig. 8 includes in the electrical circuit 209 a warning LED 215 that lights up when an unfavorable condition is detected.

Fig. 9 shows a flow chart illustrating a method for detecting an unauthorized, damaged or incompatible heater. In a first step 300, the insertion of a cartridge containing a heater into the device is detected. Then, in step 300, the electrical resistance of the heater R _1ref is measured. This occurs at a predetermined time interval after the power is applied to the heater, for example, 100 ms. In step 320, the measured resistance Ri is compared with a range of expected or acceptable resistances. The range of acceptable resistances takes into account manufacturing tolerances and differences between genuine heaters and substrates. If R ₁ is outside the expected range, then the method proceeds to step 330, where an indication is provided, such as an audible signal, and the power supply to the heater is prevented, since it is considered incompatible with the device. Then, the method returns to step 300, waiting for the detection of the insertion of a new cartridge.

Alternatively or in addition, to measure the initial resistance R _1ref in step 300, the initial rate of change of resistance can be measured during a given time interval, for example 100 ms, after power is applied to the heater. This can be done by obtaining several resistance measurements at different times during the given time interval, and then calculating the initial rate of change of resistance from the several resistance measurements and the times at which these measurements were obtained. Just as a particular heater design will have an initial resistance in the range of acceptable values, it can be expected that a particular heater design will have an initial rate of change of resistance for a given applied power within the acceptable range of the rate of change of resistance values. The calculated initial rate of change of resistance can be compared with the acceptable range of the rate of change of resistance values, and if the calculated rate of change of resistance is outside the acceptable range, then the method proceeds to step 330.

If it is determined in step 320 that R _1ref is within the range of the expected resistance, then the method proceeds to step 340. In step 340, the heater is energized for a time interval Δt ₁ , after which the difference ΔR is calculated. Advantageously, Δt ₁ is selected as a short time interval, before significant aerosol generation. In step 350, the ΔR value is compared with a range of expected or acceptable values. The range of expected values again takes into account variations in the manufacture of the heater and the substrate assembly. If the ΔR value is outside the expected range, the heater is considered incompatible, and the method proceeds to step 330, as described above, and then returns to step 300. If the ΔR value is within the expected range, then the method proceeds to step 360, in which the heater is energized to allow aerosol generation at the user's request.

Although the present invention has been described with reference to three different types of electrically heated aerosol generating systems, it should be clear that it is applicable to other electrically heated aerosol generating systems.

It should also be clear that the present invention can be implemented as a computer program product for execution on programmable controllers in existing aerosol generating systems. The computer program product can be provided as a downloadable software fragment or on a machine-readable data carrier, such as a compact disc.

The above-described exemplary embodiments are illustrative and not restrictive. Given the above-described exemplary embodiments, one skilled in the art will understand other embodiments corresponding to the above-described exemplary embodiments.

Claims (15)

1. An electrically controlled aerosol generating system comprising an electric heater comprising at least one heating element for heating an aerosol forming substrate, a power supply unit and an electrical circuit connected to the electric heater and the power supply unit and comprising a memory device, wherein the electrical circuit is configured to: measure an initial electrical resistance of the electric heater; measure a subsequent electrical resistance of the electric heater after measuring the initial electrical resistance; determine a difference between the initial electrical resistance and the subsequent electrical resistance; determine an unfavourable condition when the determined difference between the subsequent electrical resistance and the initial electrical resistance is greater than a maximum threshold value or less than a minimum threshold value, stored in the memory device; and controlling power supplied to the electrical heater based on whether an adverse condition is determined to exist or providing an indication if an adverse condition is determined to exist, wherein the difference between the initial electrical resistance and subsequent electrical resistance measurements is continuously monitored to determine whether the difference between user puffs on the aerosol generating system is less than a cooling threshold; and if it is determined that the difference between user puffs on the aerosol generating system is not less than the cooling threshold, the electrical circuit is configured to prevent or limit the supply of power to the heater until the difference is below the cooling threshold. 2. An electrically controlled aerosol generating system according to claim 1, comprising an electrically controlled aerosol generating device and a removable cartridge, wherein the power supply and electrical circuit are located in the device, and the electric heater is located in the removable cartridge, wherein the cartridge contains a liquid substrate that forms an aerosol. 3. An electrically controlled aerosol generating system according to claim 1 or 2, further comprising a puff detector for detecting the moment when the user takes a puff from the system, wherein the puff detector is connected to an electrical circuit, wherein the electrical circuit is configured to supply power from the power supply to the heating element when the puff is detected by the puff detector, wherein the electrical circuit is configured to determine the presence of an unfavourable condition during each puff. 4. An electrically controlled aerosol generating system according to claim 1, comprising a removable cartridge comprising a liquid substrate forming an aerosol and an electric heater, and an electrically controlled aerosol generating device configured to receive the removable cartridge therein in a removable manner, wherein the electrically controlled aerosol generating device comprises a puff detector for detecting the moment when the user takes a puff from the system, a power supply unit and an electrical circuit, wherein the electrical circuit is connected to the puff detector and the power supply unit and is connected during use to the electric heater, wherein the electrical circuit comprises a memory device and is configured to: measure an initial electrical resistance of the electric heater before the puff detector detects a puff; supply power from the power supply unit to the heating element upon detection of a puff by the puff detector; measure a subsequent resistance of the electric heater within a predetermined time interval after the start of supplying power from the power supply unit to the electric heater; determine a difference between the subsequent resistance and the initial resistance; comparing a difference between the subsequent resistance and the initial resistance with at least one of a maximum threshold value and a minimum threshold value stored in the memory device; determining the presence of an unfavorable condition if the difference is greater than the maximum threshold value or less than the minimum threshold value; and limiting the power supplied to the electric heater during the puff if the presence of an unfavorable condition is determined, or preventing the supply of power to the electric heater during the remainder of the puff if the presence of an unfavorable condition is determined. 5. An electrically controlled aerosol generating system according to claim 2 or 4, wherein the electrical circuit is further configured to determine when the electrical circuit is connected to the electric heater and to measure the initial resistance of the electric heater within a predetermined time interval after the electric heater is connected to the electrical circuit. 6. An electrically controlled aerosol generating system according to any one of the preceding claims, wherein the electrical circuit is further configured to: store the adverse condition determination result in a memory device; determine a number of successive adverse condition determination results based on the stored adverse condition determination results; and turn off the cartridge if the determined number of successive adverse condition determination results is greater than a maximum threshold value. 7. A heater assembly comprising an electric heater comprising at least one heating element and an electrical circuit coupled to the electric heater and comprising a memory device, wherein the electrical circuit is configured to: measure an initial electrical resistance of the electric heater; measure a subsequent electrical resistance of the electric heater after measuring the initial electrical resistance; determine a difference between the initial electrical resistance and the subsequent electrical resistance; determine when the determined difference between the subsequent electrical resistance and the initial electrical resistance of the electric heater is greater than a maximum threshold value or less than a minimum threshold value stored in the memory device; and control power supplied to the electric heater based on whether an adverse condition is determined to be present or provide an indication when an adverse condition is present, wherein the difference between the initial electrical resistance and subsequent electrical resistance measurements is continuously monitored to determine whether this difference between puffs of the user on the aerosol generating system is less than a cooling threshold value; and if it is determined that the difference between the user's puffs in the aerosol generating system is not less than the cooling threshold, the electrical circuit is configured to prevent or limit the supply of energy to the heater until the difference is below the cooling threshold. 8. An electrically controlled aerosol generating device for an electrically controlled aerosol generating system according to claim 4 or 5, wherein the electrically controlled aerosol generating device comprises a power supply unit and an electrical circuit connected to the power supply unit and comprising a memory device, wherein the electrical circuit is configured to: connect to an electric heater of the electrically controlled aerosol generating system in use; measure an initial electrical resistance of the electric heater; measure a subsequent electrical resistance of the electric heater after measuring the initial electrical resistance; determine a difference between the initial electrical resistance and the subsequent electrical resistance; determine the presence of an unfavourable condition when the determined difference between the subsequent electrical resistance and the initial electrical resistance is greater than a maximum threshold value or less than a minimum threshold value, stored in the memory device; and control the power supplied to the electric heater based on whether the presence of the unfavourable condition is determined, or provide an indication if the presence of the unfavourable condition is determined; wherein the difference between the initial electrical resistance and subsequent electrical resistance measurements is continuously monitored to determine whether the difference between user puffs on the aerosol generating system is less than a cooling threshold; and if it is determined that the difference between user puffs on the aerosol generating system is not less than the cooling threshold, the electrical circuit is configured to prevent or limit the supply of energy to the heater until the difference is below the cooling threshold. 9. An electrical circuit for an electrically controlled aerosol generating system according to any one of claims 1 to 6, wherein in use the electrical circuit is connected to an electrical heater and a power supply unit of the electrically controlled aerosol generating system, wherein the electrical circuit comprises a memory device and is configured to: measure an initial electrical resistance of the electrical heater; measure a subsequent electrical resistance of the electrical heater after measuring the initial electrical resistance; determine a difference between the initial electrical resistance and the subsequent electrical resistance; determine an unfavorable condition when a determined difference between the subsequent electrical resistance and the initial electrical resistance is greater than a maximum threshold value or less than a minimum threshold value stored in the memory device; and controlling power supplied to the electrical heater based on whether an adverse condition is determined to exist or providing an indication if an adverse condition is determined to exist, wherein the difference between the initial electrical resistance and subsequent electrical resistance measurements is continuously monitored to determine whether the difference between user puffs on the aerosol generating system is less than a cooling threshold; and if it is determined that the difference between user puffs on the aerosol generating system is not less than the cooling threshold, the electrical circuit is configured to prevent or limit the supply of power to the heater until the difference is below the cooling threshold. 10. The electrical circuit of claim 9, which in use is further connected to a puff detector for detecting when a user takes a puff from the system, wherein the electrical circuit is further configured to: determine when the electrical circuit is connected to the electric heater; measure an initial resistance of the electric heater within a predetermined time interval after the electrical circuit is connected to the electric heater; supply power from the power supply to the heating element when the puff detector detects a puff; measure a subsequent resistance of the electric heater within a predetermined time interval after the start of supplying power from the power supply to the electric heater; determine a difference between the subsequent resistance and the initial resistance; compare the difference between the subsequent resistance and the initial resistance with at least one of a maximum threshold value and a minimum threshold value; determine the presence of an unfavorable condition if the difference is greater than the maximum threshold value or less than the minimum threshold value; and limiting the power supplied to the electric heater during the puff if an unfavorable condition is determined to exist, or preventing power from being supplied to the electric heater during the remainder of the puff if an unfavorable condition is determined to exist. 11. The electrical circuit according to claim 9 or 10, further configured to: store the result of determining the unfavorable condition in the memory device; determine the number of successive results of determining the unfavorable conditions based on the stored results of determining the unfavorable conditions; and turn off the cartridge if the determined number of successive results of determining the unfavorable conditions is greater than the maximum threshold value. 12. A method for controlling the supply of power to an electric heater in an electrically controlled aerosol generating system, wherein the system comprises an electric heater comprising at least one heating element for heating an aerosol forming substrate, and a power supply unit for supplying power to the electric heater, wherein the method comprises: supplying power to the electric heater; measuring an initial electrical resistance of the electric heater; measuring a subsequent electrical resistance of the electric heater after measuring the initial electrical resistance; determining a difference between the initial electrical resistance and the subsequent electrical resistance; determining an unfavourable condition when the determined difference between the subsequent electrical resistance and the initial electrical resistance is greater than a maximum threshold value or less than a minimum threshold value; and controlling the power supplied to the electric heater based on whether an adverse condition is determined to exist, or providing an indication if an adverse condition is determined to exist, wherein the difference between the initial electrical resistance and subsequent electrical resistance measurements is continuously monitored to determine whether the difference between user puffs on the aerosol generating system is less than a cooling threshold; and, if it is determined that the difference between user puffs on the aerosol generating system is not less than the cooling threshold, preventing or limiting the supply of power to the heater until the difference is below the cooling threshold. 13. The method of claim 12, wherein the electrically controlled aerosol generating system further comprises a removable cartridge and an electrically controlled aerosol generating device configured to receive the removable cartridge, wherein the removable cartridge comprises an electric heater and a liquid substrate that forms an aerosol, and the electrically controlled aerosol generating device comprises a power supply unit, an electrical circuit and a puff detector for detecting when a user takes a puff from the system, and wherein the method further comprises: measuring an initial resistance of the electric heater before the puff detector detects a puff; supplying power from the power supply unit to the heating element when the puff detector detects a puff; measuring a subsequent resistance of the electric heater within a predetermined time interval after the start of supplying power from the power supply unit to the electric heater; determining a difference between the subsequent resistance and the initial resistance; comparing the difference between the subsequent resistance and the initial resistance with a maximum threshold value or a minimum threshold value; determining the presence of an adverse condition if the difference is greater than a maximum threshold value or less than a minimum threshold value; and limiting the power supplied to the electric heater during the puff if an adverse condition is determined to be present, or preventing the power supplied to the electric heater during the remainder of the puff if an adverse condition is determined to be present. 14. The method of claim 13, further comprising determining when the electrical circuit is connected to the electric heater, and measuring the initial resistance of the electric heater within a specified time interval after determining that the electrical circuit is connected to the electric heater. 15. A machine-readable data carrier containing a computer program product directly loaded into the internal memory of a microprocessor containing parts of the software code for performing the steps of the method according to any of claims 12-14, when said product is launched on the microprocessor in an electrically controlled aerosol-generating system, wherein the system comprises an electric heater containing at least one heating element for heating an aerosol-forming substrate, and a power supply for supplying power to the electric heater, wherein the microprocessor is connected to the electric heater and the power supply.