WO1999021031A1

WO1999021031A1 - Optical flowmeter

Info

Publication number: WO1999021031A1
Application number: PCT/DK1998/000425
Authority: WO
Inventors: Jan Kikkenborg Larsen
Original assignee: Alka Electronic ApS
Current assignee: Alka Electronic ApS
Priority date: 1997-10-07
Filing date: 1998-10-05
Publication date: 1999-04-29
Anticipated expiration: 2000-04-07
Also published as: DK114497A; AU9432598A

Abstract

The invention relates to an optical fluid flowmeter, preferably for measuring of rain, which may perform reproducible measurements under low power consumption. The invention benefits of that it is sufficient to use modulated light for obtaining optical drop registering. When using modulated light, a sufficient envelope corresponding to the effect of the drop flow of the optical path is achieved.

Description

OPTICAL FLOWMETER

The invention relates to a method as stated in the preamble of claim 1, an electronic optical flowmeter as stated in the preamble of claim 3, and an electronic flowmeter as stated in the preamble of claim 10.

There are different methods for obtaining reliable and reproducible monitoring of precipitation. One example of these is given from US patent no. 4,520,667, in which a drop collector guides precipitation to a monitoring unit, as the drop collector guides the precipitation to electrodes, which short-circuit and deliver a monitoring pulse for each of the incoming drops. The number of registered drops is thereafter converted to an evaluation signal representing the precipitation in mm, inches or corresponding units.

This technique, however, has shown to be less reliable in geographical areas, where the precipitation is quite clean, as the drops not always are capable of short- circuiting the electrodes.

US patent no. 4,314,484 discloses a rain-gauge in which electrodes are substituted with an optical registration of drops from a drop collector is known. Optical solutions, however, are problematic in many aspects, as these solutions are quite current consuming. This is in particular a problem, when using a battery as a power source

It is the object of the invention to provide a method and an apparatus, which deals with these above-mentioned drawbacks of the prior art. Background of the invention

When, as stated in claim 1, the optical transmitting means is established to modulation of the light emitted from the optical transmitting means, an effective and reproducible flow measurement having minimal power consumption has been achieved. In should in connection with fluid output be understood, that the water may be guided from the output to a reservoir or directly out of the measuring apparatus.

When, as stated in claim 2, the optical signals emitted from the optical transmitting means comprises of pulses, an particular advantageous embodiment of the invention has been achieved, as the power consumption of optical transmitting means may be further reduced.

When, as stated in claim 3, the optical transmitting means are adapted to emit modulated light in dependence of a controlling electrical signal, a possibility of obtaining an accurate flower measurement and a low power consumption has been achieved.

Thus, according to the invention, it is possible to achieve sufficient optical information at the optical receiving means when the light is modulated.

The modulation of the optical transmitting means should, within the scope of the invention, be adapted to the current applications. The modulation should in every circumstances be so that every drop is illuminated at least one time when it passes the optical path between the transmitting and receiving means. The modulation should thus be adapted to the shape of the drop as well as the drop size and the relation between minimal and maximal drop flow.

The modulation frequency may also, depending on the utilised recognition procedures, be adapted such that each drop is illumination a number of times when passing the optical path between the transmitting and receiving means .

Another adjustment that may be made within the scope of the invention is an adjustment of the modulation width, i.e. the duration of time the optical transmitting means emits a light wave a light impulse in the direction of the optical receiving means.

The shape of the curve and an eventually variation of the modulated light may also be adapted the current applications within the scope of the invention.

Further to the already mentioned advantages of claim 1, it should be mentioned that the unique combination of measuring of rain established in humid and non- encapsulated environments, need for a battery power supply and consequently a need for a low power consumption and a need for accurate and reproducible measuring is fully met and satisfied by the invention.

When, as stated in claim 4, the optical transmitting means are established to emit optical pulse signals, a particular advantageous embodiment of the invention has been achieved, as a periodic activation of the optical transmitting means may be established without the possibility of missing any drops, when carefully adjusting the electronically and optically system. It should be noted that the pulses may have several shapes within the scope of the invention. It is moreover evident, that the number of necessary light impulses is particular dependent on the current application, as the number of pulses per time unit should be adjusted in such a way, that the light impulses ensures that no drop will be disregarded because no pulse were present when the drop passed the optical path between the optical transmitting and receiving means.

The duration of the pulses may moreover be adapted suitably from application to application. The light pulse may e.g. be sustained until the drop has passed the optical path completely, thus resulting in a complete illumination during passage of the optical path. It would consequently be possible detecting the back-edge unambiguously of the drop when the front edge of the drop has entered the optical path.

The frequency and the duration of the pulses may likewise be adjusted. Another example of the "trapping" of a drop in the drop counter may be implemented by increasing the frequency of the impulses when the threshold value has been exceeded.

When, as stated in claim 5, the optical transmitting means are established to emit optical pulse signals having a constant period and a constant duty cycle, said duty cycle being the duration of the time the optical transmitting means emits light over the total period time, a particular simple and easy implementable embodiment of the invention has been achieved, as timer interrupts etc. may be performed by relatively simple and clear routines. In battery applications the invention provides a further significantly increasing of battery life time combined with a reproducible measurement. Within the scope of the invention, it is possible to adjust the period time and/or the "SET"-duration time. This adjusting may be static or dynamically as well.

In many relations it will also be attractive to let the measuring unit convert the counts of detected drops to a measure of rain over a certain interval of time, which subsequently may be shown at a monitoring unit e.g. a display.

According to a further advantageous embodiment the measuring unit may export the count measurement to a memory unit, as the measurement is moreover connected to a time of registration. Consequently the time of reading the unit becomes less critical, in the sense that all data can be collected and evaluated subsequently.

When, as stated in claim 6, the duty cycle of the pulse train is approximately 1%, and that the period time of the pulse train is approximately 32 ms, a further advantageous embodiment of the invention has been achieved, which under consideration of the electrical and mechanical features of an application, may provide a particular low power consumption combined with a very accurate registration.

When, as stated in claim 7, the rain gauge comprises a signal interface connected with the calculation means for transferring data to an external unit, said data comprising representations of the measured drop flow or processed data thereof, an advantageous embodiment of the invention has been achieved, which e.g. may be utilised in measuring units of a more professional character, as data during a certain time interval, e.g. a week, may be transferred via a memory dump to an external calculation unit, e.g. a laptop computer via the data interface.

This data interface may e.g. be wireless or be constituted by an ordinary RS-232 interface.

If a periodic readout of the above mentioned type is performed, it would typically be advantageous saving data with a reference to a time, such that the measuring of the rain may be correlated to certain specific time intervals .

When, as stated in claim 8, the calculation means converts the number of registered drops to a measure representation, which successively is displayed on a display unit, an advantageous and user-friendly application has been achieved.

When, as stated in claim 9, the distance between the optical transmitting means and the optical receiving means are approximately 10 mm when the drop size is approximately 5/100 ml, an advantageous embodiment of the invention has been achieved.

It is possible to vary the dimensioning in dependence of the desired results and mutual physical relationships between the drop size, the dynamical drop shape, the shadowing with respect to the optical system and further optical and mechanical aspects.

It should be understood that this dimensioning likewise may be supplemented with an adjustment of the means converting the rain to a drop flow of uniform drops. This adjustment may e.g. be implemented by adjustment of the drop nozzle.

If a powerful light source or sensitive receiving means is utilised, the distance between these may e.g. be increased, if desired.

When, as stated in claim 10, the means for collecting rainwater and the coupled means for converting the collected rainwater to drops is coupled to, or comprises, a filter for reduction of the drop flow fed into the drop path or the drop paths, a particular embodiment of the invention has been achieved, as it may be possible establishing a suitable slow drop flow, such that no drops will be disregarded as a result of that the drops passes the path without being illuminated during the periodic interruptions of the light

It should be understood that the design of this "max- flow" is not critical, as the functionality, i.e. a well- defined drop flow interval filter may be implemented in many designs.

When, as stated in claim 11, the filter for reduction of the drop flow comprises a sponge, a particular advantageous embodiment of the invention has been achieved, as the sponge e.g. may be inserted in the lower part of a collection funnel, and at the same time providing a maximal guidance of drops to a drop nozzle arranged in the very bottom of the collection funnel.

The sponge will in this case reduce the drop flow and moreover ensure that no water will adhere in the bottom of the funnel as a result of surface tensions, but rather be fed into the drop nozzle.

When, as stated in claim 12, in that the optical transmitting means are adapted to emit modulated light in dependence of a controlling electrical signal, a further advantageous embodiment of the invention has been achieved. Generically, the invention may be utilised for numerous different types of fluid flow, volume or weight measuring

Thus, according to the invention it is possible to establish very accurate weight or volume estimates. This feature has the consequence that the counting technique may be utilised for automatically regulated dosing.

Numerous software-based algorithms may be established for the complete recognition of a drop, when the threshold value is exceeded. Whether these algorithms determines the rest of the drop progress by means of a recognition based system by detection of the rear edge, completely detection by registration of the drop front edge, or by means of many other for the purpose convenient applications is to a great extent a choice related to the specific system parameters such as drop shape and specifications of the used electronic components.

When, as stated in claim 13, the optical transmitting means are established to emit optical pulse signals, a particular advantageous embodiment has been achieved, as a periodic activation of the optically transmitting means, when dimensioning the electrical and optical system suitably, may be established in such a way that no drops are disregarded. The figures

An example of an embodiment of the invention will be described below with reference to the drawings, in which

fig. 1 shows a preferred embodiment of the invention, and fig. 2 illustrates the light pulses utilised in a flowmeter according to the invention.

Detailed description

Fig. 1 shows the principles of a rain gauge according to the invention comprising a drop collector 1 having a output nozzle 2 in the bottom.

An output filter 3 consisting of a sponge is inserted relative to the output nozzle of the drop collector. Suitable dimensioning and positioning of the sponge relative to the output nozzle ensures that the drop flow from the output nozzle 2 consists of drops 4 which, according to the embodiment, does not exceed five drops per second.

It should be understood that the maximum drop flow depends upon the chosen dimensioning of the mechanical and electrical system.

When utilising the filter 3 one achieved advantage is that the fluid are conducted to the bottom of the drop collector without "adhering" in the input of the discharge duct in the bottom of the funnel due to surface tensions. The filter 3 will suck the fluid into the nozzle, and the capillary effect will ensure the drops are guided further. Moreover an important advantage is obtained as it may be possible to reduce the demands of the dimensioning of the optical system, as a relatively slow drop flow will reduce the risk of overlooking drops passing the optical path without being illuminated.

Thus, if the drop nozzle has a well-defined flow interval, and in particular an upper limit, a possibility of avoiding a constant illumination of the passing drop flow is avoided.

The rain gauge further comprises a light emitter 5, such as e.g. a LED 5. The light emitter is connected to a control unit 7.

The light emitter emits a light beam 8 directed to a corresponding light receiver 9. The light receiver is connected to a control unit 7 via an electrical connection 11.

The light beam emitted from the light emitter 5 will, according to the invention, be pulse shaped in the sense, the light beam is only turned on in periods.

If a drop 4 passes the optical path between the light emitter 5 and the light receiver 9 it will cause an interruption or a change of the light transmission.

The controlling unit 7, which subsequently will increment a drop counting register, will register the change. Eventually, it may be advantageous interrupting the incrementing of the drop counting register in a predefined period after the detection of that a drop has modulated the light path 8, such that further false registrations on the same raindrop is avoided. In the shown embodiment the light will be turned on for approximately 0.35 ms and turned off for approximately 32 ms, i.e. a duty cycle on approximately 1%.

Depending on the chosen electrical components, the mechanical location of transmitting and receiving means and the shape of the drops, it is possible to obtain even smaller duty cycles.

The achieved reduction of illumination time according to the invention, and the resulting reduction of power consumption is surprisingly advantageous in connection with flow measuring. The, the significant reduced power consumption combined with a reliable measuring should seen in the perspective that flow measuring is a continuously measuring going on for years.

The dimensioning of the light emitter and the performance of the light emitter should be adapted to the drop flow, such that the frequency of the light impulses sufficiently ensures that no drops will be overlooked.

Fig. 2 shows an illustration of how the pulse shape of the light emitter 5 is according to an embodiment of the invention. The pulse peaks 20 and 21 determines the time duration when the light emitter is activated.

The structure of the shown activation of the LED has form of a pulse train having a constant period and a constant duration of the activation. It should nevertheless be noted that the shape of activation is not crucial. It is therefore within the scope of the invention possible to change the period or the time duration of activation dynamically as a function of currently applicable criteria's, as e.g. the state of the system can form the basis of the mentioned changes. As an example the system could be adapted to transmit bursts of pulse trains, if no drop flow has been detected over a given period of time and then return to a constant pulse train at the first indication of a fluid flow.

Claims

1. Optical method of measuring precipitation,

said precipitation being collected by means for collecting precipitation and guided in the shape of drops to a fluid output via a measuring zone,

each drop in the measuring zone passing at least one optical path between optical transmitting means and optical receiving means,

each optical receiving means outputting an electrical signal to a calculation unit in dependence of the intensity of the light signal received at the optical receiving means,

said calculation unit being established to registration of the number of passing drops in said at least one optical path in dependence of said electrical signal,

characterised in that the optical transmitting means (5) is established to modulation of the light emitted from the optical transmitting means.

2. Method according to claim 1, characterised in that the optical signals emitted from the optical transmitting means (5) comprises of pulses (20, 21).

3. Electronically optical rain gauge comprising means for collecting rainwater and means for converting the said collected rainwater from said means into drops of certain predefined dimensions in at least one well-defined drop path,

at least one measuring zone arranged relatively to said converting means comprising optical transmitting means and optical receiving means defining at least one mutual optical path from the optical transmitting means to the optical receiving means,

said optical transmitting means being arranged for emitting light in dependence of a controlling electrical signal,

said optical receiving means being arranged to establish an electrical signal in dependence of the light received by said optical receiving means

said measuring zone being arranged in such a way that at least one of the said at least one drop paths passes at least one of the mutual optical paths,

said optical receiving means being electrical connected to calculation means, said calculation means being adapted to register the number of said passing drops in the said optical path in dependence of the said optical signal,

characterised in that the optical transmitting means are adapted to emit modulated light in dependence of a controlling electrical signal.

. Electronically optical rain gauge according to claim 3, characterised in that the optical transmitting means (5) are established to emit optical pulse signals (20, 21) .

5. Electronically optical rain gauge according to claim 3 or 4, characterised in that the optical transmitting means (5) are established to emit optical pulse signals having a constant period and a constant duty cycle, said duty cycle being the duration of the time the optical transmitting means emits light over the total period time.

6. Electronically optical rain gauge according to claims 3 - 5, characterised in that the duty cycle of the pulse train is approximately 1%, and that the period time of the pulse train is approximately 32 ms .

7. Electronically optical rain gauge according to claims 3 - 6, characterised in that the rain gauge comprises a signal interface connected with the calculation means (7) for transferring data to an external unit, said data comprising representations of the measured drop flow or processed data thereof.

8. Electronically optical rain gauge according to claims 3 - 7, characterised in that the calculation means converts the number of registered drops to a measure representation, which successively is displayed on a display unit.

9. Electronically optical rain gauge according to claim 3

8, characterised in that the distance between the optical transmitting means (5) and the optical receiving means (9) are approximately 10 mm when the drop size is approximately 5/100 ml.

10. Electronically optical rain gauge according to claim 3 - 9, characterised in that the means for collecting rainwater (1) and the coupled means for converting the collected rainwater to drops (2) is coupled to, or comprises, a filter for reduction of the drop flow fed into the drop path or the drop paths.

11. Electronically optical rain gauge according to claim 3 - 10, characterised in that the filter for reduction of the drop flow comprises a sponge (3) .

12. Electronically flowmeter comprising

means for converting a transparent fluid into drops of a predefined dimension, said drops being transmitted from the means in a well-defined drop path to a measuring zone

said measuring zone comprising optical transmitting means and optical receiving means defining at least one mutual optical path from the optical transmitting means to the optical receiving means,

said measuring zone being arranged in such a way that at least one of the said at least one drop path passes at least one of the mutual optical paths, said optical receiving means being electrical connected to calculation means, said calculation means being adapted to register the number of said passing drops in the said optical path in dependence of the said optical signal,

characterised in that the optical transmitting means (5) are adapted to emit modulated light in dependence of a controlling electrical signal.

13. Electronically optical flowmeter according to claim 12, characterised in that the optical transmitting means (5) are established to emit optical pulse signals (20, 21) .