GB2349945A

GB2349945A - Optical detection of rotation of an electricity meter disk

Info

Publication number: GB2349945A
Application number: GB9911177A
Authority: GB
Inventors: David Mackie; Samuel Antoine Bitton
Original assignee: Schlumberger Industries Ltd
Current assignee: Gemalto Terminals Ltd
Priority date: 1999-05-13
Filing date: 1999-05-13
Publication date: 2000-11-15
Anticipated expiration: 2019-05-13
Also published as: GB2349945B; GB9911177D0

Abstract

The periphery of an electricity meter disk is illuminated and an ordered sequence of pulses corresponding to the light reflected during one complete revolution is generated. In use, pulse sequences corresponding to reflected light are generated as the disk rotates and compared with this ordered sequence to determine the number of revolutions completed by the disk. The ordered sequence can be changed if variations from the expected pattern are detected in order to compensate for changes in, e.g., the position of the detector.

Description

2349945 A METHOD OF DETECTING ROTATION OF AN ELECTRICITY METER DISK, AND

APPARATUS FOR IMPLEMENTING THE METHOD The present invention relates to a method of detecting rotation of an electricity meter disk, the method comprising the following steps: illuminating the periphery of the disk, detecting the light reflected by the periphery of the disk, and generating a pulse signal corresponding to the light detected. The invention also relates to apparatus for implementing the method.

Electromechanical electricity meters have a disk which rotates at a'speed that depends on electricity consumption. Each complete revolution of the disk corresponds to a certain quantity of electrical energy being consumed. optical apparatuses are known for detecting rotation of the disk in order to deduce electricity consumption therefrom. In general, the periphery of the disk has a calibration mark that reflects poorly. The disk is illuminated, and the intensity of the light reflected diminishes each time the calibration mark moves past the light source. This drop in intensity is detected and gives rise to a count signal being emitted on each complete revolution of the disk corresponding to a determined quantity of electrical energy being consumed. 25 That method of determining electrical energy consumption is often implemented by means of apparatus external to the electricity meter and positioned on the window of the meter. A major problem arises in detecting the drop in light intensity caused by the calibration mark going past. This signal which corresponds to a pulse can be drowned in interfering pulses that are due to various sources, but mainly due to manufacturing defects or to wear on the disk which gives rise to variations in the intensity of the light it reflects.

US patent No. 4 636 637 describes a method and apparatus for detecting disk rotation. A compensation 2 circuit is provided that makes it possible to record the pulses produced by the light reflected by the periphery of the disk during a complete revolution. Thus, there is obtained, not only the pulse due to the calibration mark going past, but also a pulse profile that is the result of imperfections of the disk. Thereafter, providing the conditions under which the disk is illuminated remain constant, for each complete revolution the profile of interfering pulses is identical. For each complete revolution, this profile is subtracted from the detected signal. The resulting signal then corresponds only to the pulse generated by the calibration mark going past in isolation from interference.

That method and apparatus for implementing it suffer from the drawback of relying mainly on detecting the calibration mark. Unfortunately, for various reasons such as corrosion, wear, handling, etc., the calibration mark can be lost or can deteriorate. As a result, the measurements performed can be erroneous.

Furthermore, that method does not make it possible to take account of variations in lighting conditions and/or in detection conditions that can arise, for example, due to variations in ambient light or in the event of the illumination and/or detection apparatus being displaced relative to the disk.

The present invention makes it possible to mitigate those drawbacks. For this purpose, a sequence of characteristic pulses is derived from the light reflected by the periphery of the disk. Thus, in this case, it is no longer a question of considering the pulse profile as interfering noise to be eliminated, but as useful information. The pulse signal derived from detection is compared with the sequence of characteristic pulses. Correspondence between the two means that the disk has performed one complete revolution.

3 It will be understood that the invention operates in the same manner independently of the presence of a calibration mark.

Furthermore, the method and the apparatus of the invention can be implemented at low cost.

more precisely, the present invention provides a method of detecting rotation of an electricity meter disk, the method comprising the following steps: illuminating the periphery of the disk; detecting light reflected by the periphery of the disk; generating a pulse signal corresponding to the detected light; - comparing the pulse signal with an ordered sequence of pulses representing one complete revolution of the disk; and delivering a meter signal for each pulse signal sequence that corresponds to a pulse sequence that is representative of one complete revolution of the disk. 20 An amplitude level is given to each pulse in the pulse signal and to each pulse in the representative ordered sequence of pulses, with the comparisons being performed between amplitude levels. Said ordered sequence of pulses representing one complete revolution of the disk comprises at least one pulse of determined amplitude level.

In a particular implementation, a new pulse sequence representative of a complete revolution of the disk is made up of three pulses, each having a determined amplitude level.

A mismatch between a signal sequence and the sequence of representative pulses indicates that there has been a change in a parameter associated with the illumination of the periphery of the disk or with detection of the light reflected. This can happen when the apparatus placed against the window of the electricity meter is moved. Under such circumstances, a 4 new representative sequence of pulses is recorded to adapt to the new situation.

Preferably, a new sequence is recorded whenever at least two successive sequences are identical. This makes it possible to ensure that the sequence in question is indeed representative of the light signal reflected by the periphery of the disk.

In a particular embodiment, only pulses of an amplitude greater than a determined threshold are used for comparison purposes.

Whether relating to the representative sequence of pulses, or to pulses that are derived from measurement, by taking account solely of pulses of amplitude greater than a determined threshold it is possible to perform comparisons under good conditions, without any need to allow for small amplitude variations in light intensity.

Advantageously, only pulses of duration greater than a minimum duration are retained for comparison purposes.

In a particular implementation, the pulse signal is sampled.

In preferred manner, the periphery of the disk is illuminated and the reflected light is detected in the infrared wavelength range.

The present invention also provides apparatus for implementing the method and comprising:

emitter means for emitting a light beam towards the periphery of a disk; detector means for detecting light reflected by the periphery of the disk, and for delivering an output signal representative of the intensity of the light reflected by the periphery of the disk;. converter means connected to the output of the detector means to convert the output signal into a digital output signal; 35 - a memory in which a sequence of pulses representative of a complete revolution of the disk is recorded; and comparator means for comparing the digital output signal with the sequence of pulses representative of one revolution of the disk, and delivering a metering signal when the digital output signal corresponds to the sequence of pulses representative of one revolution of the disk.

Advantageously, the means for emitting a light beam comprise two rectangular light emitting diodes disposed one above the other, a short side of one of the diodes being adjacent to a short side of the other diode.

In advantageous manner, the detector means includes two photodetectors placed one above the other substantially parallel to the long sides of the light emitting diodes.

is In a particular embodiment, the detector means include amplifier and filter means.

Preferably, the means for emitting a light beam include means for modulating said light beam.

other features and advantages of the method and the apparatus of the invention will appear on reading the following description given by way of non-limiting indication and with reference to the accompanying drawings, in which:

Figure 1 is an overall diagrammatic view of apparatus of the invention placed on an electricity meter; Figure 2 is a fragmentary diagrammatic view of an emitter/detector unit of apparatus of the invention; Figure 3 is a block diagram of the detection system contained in the emitter/detector unit of apparatus of the invention; Figure 4 is a diagram showing the signal delivered by an emitter/detector unit; and - Figure 5 is a diagram showing the processor unit of apparatus of the invention.

Figure 1 shows apparatus of the invention placed on an electricity meter given overall reference 10. The 6 meter 10 is shown in part only, since that is all that is required for understanding the present invention, given that the meter does not form part of the invention.

The meter 10 is of the electromechanical type, and comprises a disk 12 which rotates at a speed that is proportional to the rate at which electrical energy is being consumed. Rotary drive is provided by a mechanism that is not shown but that is well known to the manufacturers of electricity meters. The disk 12 is visible behind a transparent window 14.

The apparatus of the invention as shown in Figure 1 comprises two units 16 and 18 which are interconnected, however it would naturally be possible to implement the apparatus as a single unit.

The emitter/detector unit 16 is designed to be fixed on the window 14 of the meter 10 by any appropriate means. For instance it can be glued on the window 14.

Figure 2 is a diagram showing a portion the unit 16. It has a front face 20 that is transparent at least to infrared radiation and that is designed to be placed looking into the window 14 of the meter 10.

Advantageously, the front face 20 is designed to be placed against the window 14 so as to avoid interfering light. The unit 16 has means for emitting a beam of light towards the periphery of the disk 12. In the example shown, these means are constituted by two light emitting diodes (LEDs) 22 and 24. These LEDs are of rectangular shape, being placed with the small side of one against the short side of the other. Thus, the long sides of the LEDs are disposed substantially perpendicularly to the plane of the disk 12 so as to extend the range of illumination and thus make positioning of the unit 16 less critical where it faces the disk 12.

The LEDs 22 and 24 emit infrared light in the wavelength range 850 nm to 950 nm.

7 The two LEDs 22 and 24 are connected in series and are powered by not shown power supply unit which derive + 5v d.c. by stepping down the mains a.c. voltage with a transformer and then rectifying it Also, by means of the command supplied by appropriate means to which they are connected, e.g. a microcontroller located in the unit 18, the LEDs emit respective light beams that are modulated in time. The modulation frequency of the light beams can be selected to be of the order of a few kilohertz, e.g. 8 kHz. This modulation serves to distinguish light from the LEDs and reflected by the periphery of the disk 12 from noise due to detecting ambient light, and thus makes it possible to filter out the noise.

Behind the front face 20 of the unit 16, to one side of and parallel to the LEDs 22 and 24, two photodetectors 26 and 28 that are sensitive to infrared light are placed one above the other so as to detect the light reflected by the periphery of the disk 12. The use of two photo- detectors that are superposed in a manner similar to the LEDs, makes it possible to extend detection coverage and contributes to making the positioning of the unit 16 less critical. The protectors are connected in parallel and their outputs are interconnected so that, in effect, the photodetectors deliver a single output signal. The photoprotectors are powered by the above mentioned power supply unit. Figure 3 is a block diagram of the elements provided for detection purposes and contained in the unit 16. 30 The photodetectors 26 and 28 deliver an electrical signal that is proportional to the intensity of light they detect. Variations in this electrical signal are representative of variations in the intensity of light reflected by the features and faults of the periphery of the disk 12. These variations are in the form of pulses of different amplitudes. Also, the profile of these variations is identical for each complete revolution of 8 the disk, providing lighting and detection conditions remain constant.

The electric signal is in the form of a small current which is amplified by a first amplifier stage 30 which also provides a first stage of filtering to eliminate high frequency noise signals. In the present example where the light signal is modulated at 8 kHz, this filtering can be implemented so as to attenuate all signals of frequency greater than 9.4 kHz.

This type of amplifier stage is well known and its implementation does not need to be described in detail. The first amplifier stage 30 delivers an amplified and filtered signal on an output. Said output is connected to an input of a filter stage 32 which performs highpass filtering with a cutoff frequency equal to 7.2 kHz, for example, and which serves to reduce noise due to the photodetectors 26 and 28 detecting ambient light. This type of filtering can be obtained by means of a CR (capacitor and resistor) filter or by any other equivalent filter. The filtered signal is delivered on an output of the filter stage 32 which is connected to an input of a second amplifier stage 34. The signal at 8 kHz is amplified merely in order to obtain a signal that is amplified, but without saturating the second amplifier stage. CR filters and this type of amplifier stage are well known and there is no need for a detailed description of their implementation. The amplified signal is delivered on an output which is connected to an input of a peak detector 36 which serves to detect changes in the amplitude of the amplified signal. A diode D allows capacitor C to instantaneously charge up to the peak of the modulated input and so removes the 8kHz modulation. The resistor R allows capacitor C to discharge if the input signal gets smaller. The peak detector 36 output is thus a varying d.c. voltage which tracks the infra red light returned from the disc.

9 The signal from the peak detector is delivered on an output which is connected to the input of a third amplifier stage 38 which amplifies the signal by a factor of 2, for example. This type of amplifier stage is well 5 known and is not described in detail herein.

The third amplifier stage 38 delivers the amplified signal on an output which is connected to an input of a low pass filter 40 for eliminating the noise generated by the preceding amplifier stages.

The filter 40 serves to eliminate pulses of width smaller than 20 ms, for example (cutoff frequency 50 Hz) so as to retain only those pulses that are of greater width, thereby facilitating subsequent processing. It is implemented, for example, merely by an RC filter (resistor and capacitor). In equivalent manner, the low pass filter can also be implemented as an active filter. The filtered signal is delivered on an output which is also an output of the unit 16 which is connected to an input of the unit 18. 20 Figure 4 is a diagram showing a typical signal delivered by an emitter/detector unit 16. The recording shown corresponds to variations as a function of time in the amplitude of the light signal reflected by the periphery of the disk 12 when it is rotating at constant speed. As can be seen, the signal is periodic and one period corresponds to one revolution of the disk 12. If the speed of rotation of the disk 12 varies, then the signal is no longer periodic, but the amplitude characteristics of the pulses remain constant. Thus, pulses 1, 4, and 7 have the same amplitude, as do the pulses 2 and 5 and the pulses 3 and 6.

Figure 5 is a block diagram of the contents of the processor unit 18.

The unit 18 mainly comprises a microcontroller 42 having the usual peripherals such as memories, and an interface for connection to a network (not shown in Figure 4),...

The microcontroller is powered by the above mentioned power supply unit.

The microcontroller 42 converts the signal delivered by the unit 16 into a digital signal, for which purpose preliminary sampling is performed. This sampling is performed at a frequency that is not less than 100 Hz, for example.

Thereafter, the microcontroller processes the digital data by comparing it with an ordered sequence of pulses representative of one complete revolution of the disk. This digital sequence is recorded on starting and then automatically, whenever necessary, as explained below.

The input signal is thus made up of successive is pulses each characterized by a digital amplitude level.

A minimum noise amplitude is defined during initial programming of the microcontroller 42. The amplitudes of pulses are identified in the microcontroller 42 by means of two determined amplitude levels (see Figure 4). Each amplitude level is equal to twice the minimum noise level amplitude.

If amplitude variation is less than the minimum noise amplitude, then the microcontroller 42 maintains the same amplitude level for the pulse, thereby enabling the microcontroller to take account of characteristic pulses only. Similarly, a pulse is recognized as a pulse by the microcontroller 42 only if its amplitude is greater than the minimum noise level. 30 The representative pulse sequence is recorded in ordered manner, and more particularly the amplitude levels of each of the pulses are recorded. Assuming that measurement conditions remain unchanged, and taking account of the periodic nature of the input signal, rotation of the disk through one complete revolution gives rise to a first input signal pulse which must correspond to the first pulse of the 11 representative sequence. The amplitude level of the following pulse must correspond to the following pulse in the representative sequence, and so on. The term "correspond" is used to mean that the amplitude levels of 5 the pulses are the same.

Under such conditions, successive pulses in the input signal are compared with successive pulses in the representative sequence. Each time the successive amplitude levels of the pulses in the input signal correspond to those of said sequence, the microcontroller 42 issues a metering signal on an output. The metering signal can then be used to determine overall electricity consumption by summing or it can be subjected to any appropriate processing by the microcontroller itself or by any other apparatus provided for this purpose.

If the amplitude level of a pulse forming a portion of the input signal does not correspond to the expected amplitude level in the representative pulse sequence, the microcontroller 42 then records a new sequence of representative pulses that replaces the presentlyrecorded sequence. A mismatch between the pulse in the input signal and the pulse expected from said sequence means that a parameter has changed concerning illumination of the periphery of the disk or concerning detection of light reflected by the periphery of the disk. For example moving the unit 16 will have this type of consequence.

For this purpose, the microcontroller 42 records the successive amplitude levels of the pulses in the input signal until the run of pulses repeats, at which point the disk will have performed one complete revolution. In order to avoid any risk of error, the microcontroller preferably compares at least two successive sequences and waits until it has received three identical sequences, for example, before recording the representative pulse sequence and restarting metering.

12 The loss of three disk revolutions for metering purposes is of no significant incidence on measuring the total electricity consumption.

This process of recording the representative ordered sequence of pulses is the same as that implemented on starting for determining the first reference sequence which is subsequently modified only when the microcontroller 42 detects a mismatch between the input signal and the representative sequence, as described above.

It will be understood that the method implemented by the apparatus is independent of time. If electricity consumption should be interrupted, it follows that the disk will stop turning. The input signal seen by the microcontroller 42 will then be a substantially constant signal that varies little, with variation being due to noise only. However, as mentioned above, if variations in the signal do not exceed a certain threshold, then the amplitude level is kept constant by the microcontroller 42. In this way, comparison with the representative pulse sequence is suspended. It will only restart when a pulse is formed, i.e. when significant variations reappear in the input signal due to the disk rotating.

In the embodiment shown in the figures, the microcontroller 42 is used to control modulation of the LEDs at the frequency of 8 kHz.

Claims

1/ A method of detecting the rotation of an electricity meter disk, the method comprising the following steps:

illuminating the periphery of the disk; detecting light reflected by the periphery of the disk; and - generating a pulse signal corresponding to the detected light; the method being characterized in that it further comprises the following steps:

- comparing the pulse signal with an ordered sequence of pulses representing one complete revolution of the disk; and delivering a meter signal for each pulse signal sequence that corresponds to a pulse sequence that is representative of one complete revolution of the disk.

2/ A method according to claim 1, in which an amplitude level is given to each pulse in the pulse signal and to each pulse in the representative ordered sequence of pulses, with the comparisons being performed between amplitude levels.

3/ A method according to claim 2, in which said ordered sequence of pulses representing one complete revolution of the disk comprises at least one pulse of determined amplitude level.

4/ A method according to claim 3, in which said sequence of pulses representative of one complete revolution of the disk comprises three pulses each having a determined amplitude level.

5/ A method according to any one of claims 2 to 4, in which a new ordered sequence of pulses representative of one complete revolution of the disk is recorded each time the amplitude level of a pulse in the pulse signal does 14 not correspond to the amplitude level of the pulse expected from the present representative ordered sequence of pulses.

6/ A method according to claim 4, in which a new sequence is recorded whenever at least two successive sequences are identical.

7/ A method according to any preceding claim, in which only pulses of an amplitude greater than a determined threshold are used for comparison purposes.

8/ A method according to any preceding claim, in which only pulses of duration greater than a minimum duration is are used for comparison purposes.

9/ A method according to any preceding claim, in which the pulse signal is sampled.

10/ A method according to any preceding claim, in which the periphery of the disk is illuminated and the reflected light is detected using wavelengths in the infrared range.

11/ Apparatus for implementing the method according to any one of claims 1 to 10, characterized in that it comprises: - emitter means for emitting a light beam towards the periphery of a disk; 30 - detector means for detecting light reflected by the periphery of the disk, and for delivering an output signal representative of the intensity of the light reflected by the periphery of the disk;. converter means connected to the output of the detector means to convert the output signal into a digital output signal; is - a memory in which a sequence of pulses representative of a complete revolution of the disk is recorded; and comparator means for comparing the digital output signal with the sequence of pulses representative of one revolution of the disk, and delivering a metering signal when the digital output signal corresponds to the sequence of pulses representative of one revolution of the disk. 10 12/ Apparatus according to claim 11, in which the means for emitting a light beam comprise two rectangular light emitting diodes disposed one above the other, a short side of one of the diodes being adjacent to a short side is of the other diode.

13/ Apparatus according to claim 12, in which the detector means includes two photodetectors placed one above the other substantially parallel to the long sides 20 of the light emitting diodes.

14/ Apparatus according to any one of claims 11 to 13, in which the detector means include amplifier and filter means. 25 15/ Apparatus according to any one of claims 11 to 14, in which the means for emitting a light beam include means for modulating said light beam.