RU2258260C2 - Smoke alarm - Google Patents

Abstract

FIELD: fire alarm systems.

SUBSTANCE: device has photo-detector with RC circuit with length of charge/discharge cycle dependent on light flow of light pulse source, and controller for determining smoke level or dust level on basis of length of photo-detector discharge. Current device can be used to find suspended particles of dust, fog, etc. in surrounding environment.

EFFECT: broader functional capabilities, higher efficiency.

5 dwg

Description

The proposed solution relates to fire alarm devices for detecting smoke at an early stage of ignition and can be used to detect the presence of suspended particles (dust, fog, etc.) in the environment.

A known smoke detector (patent 660244, Switzerland, G 08 B 17/10, 29/00 from 03/31/87), containing an optical camera, a generator that controls the radiation source, amplifier, signal processing circuit. The optical signal reflected from the smoke particles enters the photodetector, amplified and fed to the signal processing circuit. When the optical channel is dusty, smoke detection at an early stage of ignition is difficult, and sometimes impossible. The lack of dust control reduces the reliability of this device and is its disadvantage.

A known smoke detector (RF patent 2125739, G 08 B 17/10 from 01/27/99), selected as a prototype, containing a generator connected to an optical radiation source, a photo detector connected to a photocurrent amplifier, which is connected to an amplifier through a high-pass filter a shaper whose output is connected to the input of the RS-trigger. The trigger output is connected to the first input of the And element and to the C input of the counter, and the second driver is connected to the control input of the amplifier-former. The optical signal reflected from the smoke particles enters the photodetector, is amplified by a photocurrent amplifier, is synchronously filtered and fed to the signal processing circuit.

Known smoke detectors work on the principle of periodically emitting light pulses and then receiving an optical signal reflected from the smoke particles by the photosensor, further amplifying it using various analog amplifying devices (transistor stages, operational amplifiers, etc.), comparing with the reference voltage and outputting signal about the presence or absence of smoke.

The disadvantages of the prototype should include

- the use of analog devices;

- lack of control of the operability of the optical channel during operation; when the prototype is in operation, the failure of the optical channel (emitter, photodetector, amplifiers) is adequate to give a “no alarm” signal in the presence of smoke or to give a false alarm “fire”;

- lack of control of dustiness of the optical channel.

The objective of the technical solution is to create a reliable smoke detector, which allows, in particular, to control the operability and dustiness of the optical channel, eliminate analog devices and make a complete transition to digital circuitry.

The task in a smoke detector containing a control circuit connected to the detector, a light pulse source connected to another output of the control circuit and optically coupled to the photodetector is achieved by the fact that the photodetector is directly connected to a bi-directional logical port that is connected to the control circuit.

Figure 1 shows a block diagram of a smoke detector. Figure 2 shows a block diagram of a smoke detector, in which a bi-directional logic port and control circuit are made in the form of a controller. Figure 3 shows the equivalent model of a photodetector. Figure 4 shows the timing diagram of the discharge of the photodetector. Figure 5 shows a schematic diagram of the smoke detector of figure 2.

The smoke detector (Fig. 1) contains a light pulse source 1, optically coupled to a photodetector 2, which is connected to a bi-directional logic port 3, an alarm 4, the input of which is connected to the output of the control circuit 5, the other output of which is connected to the input of the light pulse 1, bidirectional logical port 3, connected to control circuit 5.

The smoke detector (figure 2) contains a light pulse source 1, optically coupled to a photodetector 2, which is connected to the logical port of the controller 6, which acts as a bi-directional logical port 3 and control circuit 5, the signaling device 4, the input of which is connected to the output of the controller 6, input the source of light pulses 1 is connected to the output of the controller 6.

The smoke detector (Fig. 5) contains, in principle, a controller 6 - AT90S1200 (DD1), a light source 1 - an infrared diode of the AL164B1 (VD1) type with a current-limiting resistor R1 = 120 Ohm, a photodetector 2 of the KDF115 type, and the signaling device 4 according to the principle circuit in the form of a sound element ЗП1 of type ППА1 and LED VD3 of type АЛ307 with current limiting resistance R2 = 500 Ohm, С - storage capacitance of type K-50-35 - 100 μF. The smoke detector is connected to a + U power supply with a voltage of 4.5-6 V.

Consider the principle of operation of the proposed smoke detector. Let photodetector 2 be an element of the RC circuit (Fig. 3), in which one or both elements are simultaneously sensitive to the light flux F. (R = f (Ф) or С = f (Ф.)). Thus, the duration of the charge (discharge) cycle will also depend on the light flux τ = RC = F (Ф) (Fig. 4). The optical signal emitted by the source of light pulses 1 is reflected from the smoke particles, enters the photodetector 2 and changes the duration of the charge (discharge) cycle.

In the smoke detector there is an optical connection between the source of light pulses 1 and the photodetector 2 even without smoke. This optical coupling can be used to determine the dustiness and serviceability of the optical channel.

The smoke detector operation algorithm consists of the following steps. Measure the duration of the cycle t ₁ (Fig. 4) of the charge (discharge) of the photodetector 2, to a certain threshold level U _P , in the absence of light flux from the source of light pulses 1, then turn on the source of light pulses 1 and re-measure the duration of the cycle of charge (discharge) t ₂ photodetectors 2, then find Δt = | t ₁ -t ₂ |. In this case, the influence of destabilizing factors (such as background illumination, temperature, etc.) is subtracted and only the change in the charge Δt time (discharge) caused by the action of the optical emitter remains. Then Δt is compared with the threshold settings Δt ₁ , Δt ₂ ... Δt _n . For example, if Δt ₂ <Δt <Δt ₃ , then this may correspond to the absence of smoke and the integrity of the optical channel, if Δt ₁ <Δt <Δt ₂ - the optical channel is dusty, if Δt <Δt ₁ - the optical channel is faulty, if Δt> Δt ₄ - the presence of smoke.

In a practical implementation, it is convenient to use the time - number of pulses transformation for measuring t ₁ and t ₂ (similarly to the principle of operation of an analog-to-digital converter with a time-pulse conversion) N1 = t ₁ f _g , N2 = t ₂ f _g , where f _g is the clock pulse generator frequency. In this case, the difference Δt = | t ₁ -t ₂ | - is proportional to the difference in the number of pulses k = | N1-N2 | = f _g | t ₁ -t ₂ |.

Reaching the threshold level U _{P is} controlled by a threshold device, which can be performed on logic elements. In this case, the photodetector 2 is directly connected to the logical port. For logic elements with high input impedance (CMOS - series), the switching threshold from a logical unit to a logical zero, as a rule, is equal to half the supply voltage of the microcircuits. In this case, the number of pulses is measured, during which the voltage at the photodetector 2 from a logical unit reaches a logical zero.

The use of controller 6, with the proposed time-pulse conversion, reduces the number of elements, makes it possible to carry out multiple measurements with averaging their results, eliminate systematic errors, automatically control the correct operation of the device, and correct errors caused by the dustiness of the optical camera.

The smoke detector of figure 2 works as follows. In the memory of the controller 6, predefined threshold values k1, k2, k3 are recorded. The port of the controller 6, to which the photodetector 2 is connected, is set to a high state (the photodetector capacitance is charging), then this port of the controller 6 is switched as the input with a high resistance, and the internal counter (timer) of the controller 6 is turned on, the count of which stops when the controller input 6, to which photodetector 2 is connected, is discharged to the level corresponding to logical zero, while the logical port of controller 6 plays the role of a threshold device. This state of the counter (N1) is remembered by the controller 6. Then, the controller port 6, to which the photodetector 2 is connected, is again set to a high state (the capacity of the photodetector 2 is charged), then the controller 6 turns on the light source 1, sets the controller port 6 to which photodetector 2 is connected as an input with high resistance; at the same time, the internal counter (timer) of controller 6 is turned on, the count of which is stopped when the input of controller 6, to which photodetector 2 is connected, is discharged to corresponding to logical zero, this counter state (N2) is stored by controller 6. Controller 6 turns off the light pulse source 1. There is a difference k = N2-N1, which is compared with threshold values k1, k2, k3 by controller 6. If k2 <k <k3, then the smoke detector is operational, the optical channel is dust free, and there is no smoke. If k1 <k <k2, then the controller 6 includes a signaling device 4, which gives a signal characterizing the dustiness of the optical channel. If k <k1, then the controller 6 includes a signaling device 4, which generates a signal indicating a malfunction of the optical channel. If k> k3, then controller 6 turns on alarm 4, which gives an alarm indicating the presence of smoke. The signals for each type of alarm are different from each other.

The threshold values k1, k2, k3 can be determined as follows.

Measure the smoke detector k = k0, in the absence of smoke, the dustless optical channel (intrinsic state of the optical channel of the smoke detector), and determine k2 = 0.7k0. Place the smoke detector in a smoke chamber with bright smoke, the optical density of which is, for example, 0.1 dB / m, measure k = k3. Then determine k1 = 0.1k0.

Consider the influence of destabilizing factors. Suppose that the RC circuit (figure 4) is charged to a voltage of U ₀ . The discharge of such a circuit is carried out according to the well-known law U = U ₀ exp (-t / τ), where τ = RC. The discharge time will be measured to a certain threshold level Uп. It is assumed that the time constant is sufficiently small and the measurement of time intervals t1 and t2 is carried out directly one after another, therefore, the change in the threshold level Uп, background illumination Φ and temperature per measurement cycle can be neglected. With a change in the supply voltage and temperature, U ₀ also changes, as well as Uп (Uп / U ₀ -const) linearly associated with it. Consider how this affects the operation of devices. The time intervals t1 and t2 are determined from the expressions

Uп = U ₀ exp (-t1 / τ1),

Uп = U ₀ exp (-t2 / τ2),

where τ1 = R1 • Cl and τ2 = R2 • C2 are the time constants of the circuit in the absence and presence of a light flux pulse. By logarithm and simple transformation, we determine the time intervals t1, t2:

t1 = τ1 ln (Uп / U ₀ ),

t2 = τ2 ln (Uп / U ₀ ).

Find Δt

Δt = | t ₁ -t ₂ | = | τ1 ln (Uп / U ₀ ) -τ2 ln (Uп / U ₀ ) | = | τ1-2 | ln (Uп / U ₀ ).

Therefore, Δt = | t ₁ -t ₂ | independent of voltage U ₀ .

Consider the effect of background illumination and temperature. Let the resistance R = f (Ф) of the photosensor be sensitive to the light flux. This resistance can be represented as R = R0 + ΔR (Ф ₀ ) + ΔR (Фи) + ΔR (T), where R ₀ is the resistance of the photodetector in the absence of light, ΔR (Ф ₀ ) is the change in resistance caused by the influence of background illumination, ΔR (Phi) is the change in resistance when the light flux hits the photodetector from a source of light pulses, ΔR (T) is the change in resistance of the photodetector under the influence of temperature. Using the above calculations, we find Δt:

Δt = ln (Up / U ₀ ) | τ1-τ2 | = ln (Up / U ₀ ) | R1 • C-R2 • C | = ln (Up / U ₀ ) | [R0 + ΔR (Ф ₀ ) + ΔR (T)] • C- [R0 + ΔR (Ф ₀ ) + ΔR (Т) + ΔR (Фи)] PС | = ln (Uп / U ₀ ) ΔR (Фи) • С

Thus, Δt = | t ₁ -t ₂ | It does not depend on the background illumination and temperature and, therefore, does not reduce the sensitivity of the smoke detector.

The smoke detector is easily implemented on a modern element base (figure 5). In this case, the Atmel-based microcontroller AT90S1200 (DD1) was used as controller 6, based on field-effect transistors, with a built-in clock generator that does not require external elements and has a frequency f _g , an eight-digit timer-counter, bidirectional logic ports PD and РВ, which can work as input or output ports. Input impedance over 100 megohms. The source of light pulses 1 is an infrared diode of the AL164V1 (VD1) type with a current-limiting resistor R1 = 120 Ohm, a photodetector 2 of the KDF115 type, a signaling device 4 - of an audio element ZP1 of the PPA1 type and a VD3 LED of the AL307 type with a current-limiting resistance R2 = 500 Ohm, C - storage capacity type K-50-35 -100 uF. The smoke detector is connected to a + U power supply with a voltage of 4.5-6 V.

The algorithm of the smoke detector (figure 5) is as follows. In the memory of the controller 6, predefined threshold values k1, k2, k3 are recorded. The ports of controller 6 PD0, PD5, PB4, PB1 are set as output to high state, the other ports are disabled. When the PD5 port is set to a high state, the capacitance of photodetector 2 is charged. Then the PD5 port of controller 6 is initialized as an input with a high resistance, while the internal pulse counter of the internal clock of controller 6 is turned on, which stops when the voltage at the photodetector 2 of controller 6 connected to PD5 port is have a level equal to logical zero. This counter state is memorized (N1). Then, the PD5 port of controller 6 is again set to high and the capacitance of photodetector 2 VD2 is charged. The PD5 port of controller 6 is initialized as an input with a high resistance, the PDO port is turned on as an output in a low state, while a current flows through the diode VD1, which is a source of light pulses 1, while the internal pulse counter of the internal clock of controller 6 is turned on, which stops when the voltage at the photodetector 2 of the controller 6 connected to the PD5 port will have a level equal to logical zero. This counter state is again remembered (N2) by the controller 6, and the light pulse source 1 - VD1 is turned off. The difference k = N2-N1 is found, which is compared with the threshold values k1, k2, k3 by controller 6. If k2 <k <k3, then the smoke detector works normally, there is no smoke, the camera is dustless. The VD3 LED turns on briefly through the PB4 port, indicating that the fire detector is operating normally. Next, the cycle of operation of the controller 6 is repeated from the beginning. If k1 <k <k2 and this state is repeated many times over a long period of time (for example, within ten minutes), then the controller 6 sends short-term pulses through the port РВ1 in the sound range to control the signaling device 4 ЗП1, which characterize the dustiness of the optical channel. If k <k1, and there was no state k1 <k <k2, then the controller 6 through the port РВ1 gives short-term pulses in the audio range, indicating a malfunction of the optical channel. These sound pulses are different from those that show the dustiness of the optical channel. If k> k3, then through the port РВ1 a continuous alarm signal of frequency f2 is issued to the signaling device 4 ЗП1, indicating the presence of smoke.

Thus, in comparison with the prototype, the proposed smoke detector is made entirely on digital circuitry, provides control over the operability and dustiness of the optical channel during operation, which increases the reliability of its operation.

Claims (1)

A smoke detector containing a signaling device and a light pulse source optically coupled to a photodetector, characterized in that a controller is inserted into it, and the photodetector has an RC circuit with a charge (discharge) cycle depending on the light flux of the light pulse source reflected from the smoke particles , the controller has a memory for recording threshold values and a counter, the count of which is turned on when the photodetector is connected to the controller, and stops when the photodetector is discharged with the counter state N1, which is stored, the controller is designed to turn on the source of light pulses, turn on the counter when the photodetector is connected, and stop the counter with the state N2 when the photodetector is discharged, also to find the difference k = N2-N1 and compare with the indicated threshold values, the controller is designed to turn on the signaling device, the signals of which are of the types of anxiety are different from each other.

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