GB2192708A

GB2192708A - Optical sensor for meters

Info

Publication number: GB2192708A
Application number: GB08617632A
Authority: GB
Inventors: Calogero Condello; Richard Ward
Original assignee: British Gas Corp; British Gas PLC
Current assignee: British Gas Corp; British Gas PLC
Priority date: 1986-07-18
Filing date: 1986-07-18
Publication date: 1988-01-20
Anticipated expiration: 2006-07-18
Also published as: GB8617632D0; GB2192708B

Abstract

An electro-optical sensor arrangement which records the number of revolutions of a meter index pointer includes a phototransducer comprising L.E.D. 3 and a photo-transistor 5 which normally receives light pulses reflected from a meter dial 8 to provide a pulsed input signal to a signal processing circuit. The processing circuit comprises a Schmitt trigger 4a, b, which receives clock pulses five times per second from a timer 1, and a flip-flop 11a, b the output Q of which is normally high and is feedback connected via diode 12 and resistor 13 to the data input of the Schmitt trigger. The output Q goes high only when the pointer interrupts the path of I.R. beam 7, whereby a a pulse is fed to a logger (not shown) via monostable 14 and switch 15. The flip-flop does not reset until substantially the whole pointer passes out of the beam path, so that slow travel or hesitation of the pointer does not produce false pulses to the logger. <IMAGE>

Description

SPECIFICATION Optical sensor for meters The present invention relates to an optical sensor for meters and, more particularly, to an electro-optical sensor which senses the number of revolutions of a meter index marker.

In the past, meter readings, such as domestic gag meter readings, have been taken mantially by visual inspection of, for example, dials mounted behind one or more windows provided in the meter casing.

Previous attempts by others to provide electro-optical sensors for logging for example, gas consumption, have involved attaching the sensors to a gas meter to sense the passage of meter index pointer through a light beam and thus enable recording of the revolutions of the pointer. However, it has been found that when the gas pilot lights only. were on, the loggers recorded se.veral times the actual gas rate, i;e. too high a gas consumption figure. This was a result of multiple pulses being created and recorded as the index pointer just started to interrupt the optical path or had just left the optical path. At these positions, the movement of the meter index pointer, as a result of vibration of the pointer or the surrounding plant, caused the optical path -to be interrupted several times during the same revolution of the index pointer.Thus the logger recorded several pulses instead of one pulse for the one actual pass of the pointer -across the optical path.

An object of our invention is to- eliminate or substantially remove the possibility of sensing and recording such multiple-pulsing.

To this end the invention consists in an electro-optical sensor arrangement for detecting movement of a meter index marker through a light beam comprising a pulse generator connected to a light emitting means, a photo-transducer for receiving light pulses emanating from the light emitting means and providing a pulsed input signal to a signal processing circuit which provides a pulsed output recorded by a recording means when the strength of -said pulsed input falls to a predetermined trigger magnitude whereat the circuit is triggered from a first state to a second state to cause a further fall in the strength of the pulsed input, the circuit returning to its first state when the strength of the pulsed input rises to the trigger magnitude whereat the circuit is triggered to cause a further increase in the pulsed input strength.

The signal processing circuit may include a Schmitt trigger and a feedback loop for connecting a Schmitt trigger output to the Schmitt trigger input which receives said pulsed input signal. The feedback loop is normally non-conducting, that is when the circuit is in its first state. Once the strength of the pulsed input signal falls to the trigger magnitude, the feedback loop becomes conducting and said -input signal is shared between the feedback loop and the Schmitt trigger input to cause the further fall in the strength of the actual input signal to the Schmitt trigger. For example, the strength of the input signal may fall by substantially 50% in magnitude, say from a trigger voltage of substantially 2.5 volts down to 1.25 volts, so that 1.25 volts is applied to the feedback loop and 1.25 volts the Schmitt trigger input.In this example when the actual input to the Schmitt trigger rises to 2.5 volts i.e. the trigger voltage, the voltage applied to the feedback loop is also 2.5 volts.

At this trigger voltage the feedback loop reverts to being non-conducting with the result that the actual input signal to the Schmitt trigger increases further, in this example buy 100%, to 5 volts.

The feedback loop may include a reverse bias diode and a series resistor. An output from the Schmitt trigger may provide an input signal to a flip-flop which may form part of the feedback loop.

In order that the invention may be more readily understood, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a block diagram of one embodiment of the invention, and Figures 2 and 3 show in diagramatical form, respectively, the absence of and presence of a meter index pointer in the optical path between the light emitting means and the phototransducer.

With reference to Figure 1, a cmos 555 timer 'chip' 1 provides a 200 microsecond pulse at a repetition rate of, say, 5 pulses per second. These pulses are amplified by a 'Darlington' transistor pair 2. The pulses from the output of amplifier 2 divides into two pulse trains. One pulse train is applied to an infrared light emitting diode (IR LED) 3 in a sensor unit.

The other path pulse train is applied to an inverting Schmitt trigger 4583B (part A) 4a which forms one part of a two part (part A and part B) 4a, 4b Schmitt trigger integrated circuits chip.

The return electrical circuit from the IR LED includes a current limiting resistor in series with a variable resistor (not shown). The limiting resistor is to prevent overloading the IR LED, whilst the variable resistor permits setting up of the system.

As shown in Figures 2 and 3 the IR LED 3 and a phototransistor 5 are arranged facing a meter dial 6 so that the beam 7 emitted by the IR LED is reflected by the backplate 8 of the dial and/or by revolving pointer 9 of the dial. Beam pulses reflected by the backplate fall on the phototransistor and are converted into electrical pulses which are amplified by transistor 10 and then applied to the input of part B of the Schmitt trigger 4b.

Part A and Part B of the-Schmitt trigger produce squared output pulses which, respectively, are applied to clock and data inputs, 1 lea, 1 ib, of a 4013B flip-flop. There.are two respective outputs from the flip-flop, Q and Q Output O is normally high (logic 1), e.g.

when no part of the meter index pointer 9 interrupts the light beam, and is connected to the input of part B, 4b, of the Schmitt trigger via a reverse bias diode 12 and a series resistor 13 to provide a feedback loop.

Output 0. from the flip-flop is normally low (logic 0) and is connected to the input of a 'monostable chip' 4047B, 14. The output from monostable 14 is applied to part A of a solid state switch 4016, 15, the output from which provides the input to a compatable pulse data logger (not shown).

A 9 volt battery pack (not shown) may be used to supply the voltage.

In order to maintain a. substantially constant supply voltage, a voltage regulator (not shown) set to supply 6 volts is provided.

The functioning of the present embodiment of the electro-optical sensor according to the invention will now be described.

During the period before the meter index pointer 9 starts to interrupt the light beam emitted from the IR LED 3, maximum light is reflected. -from the dial back-plate 8 to the phototransistor 5. The equipment is so set up that a pulsed 5V output from the phototransistor is applied to the- Schmitt trigger (part B), 4b. The output from the Schmitt trigger (part B) forms the input to the data input 1 1b of the flip-flop which provides an output of 5V (or logic 1) resulting in the feedback loop remaining in- a non-conductive state.For the same pulsation. a 5V input is also applied to the Schmitt trigger (part A) 4a to provide an inverted signal which in turn is applied to the clock input 1 1a of the flip-flop from which there is no output (or logic 0) and therefore no signal for the logger.

When the meter index pointer 9 starts to.

cut the optical path and moves across the beam, progressively less- and less light is reflected by the dial backp!ate 8 to the phototransistor 5 until 50% of the maximum reflected light falls on the phototransistor to provide a 2.5V pulsed output which is applied to Schmitt trigger (part B) 4b. Over the voltage range 5V down to nearly 2.5V input for the Schmitt trigger (part B) 4b the circuit functions as described above for a 5V input. Thus the logger has still not received an input signal.

Once the meter index pointer9 moves further across the beam the output from the phototransistor 5 falls below 2.5V (the trigger voltage) whereupon the output from the Schmitt trigger (part B) 4b becomes low (or logic 0). -The signal to the data input 1 1b of the flip-flop is also low, with the result that the data output 0 of the flip-flop is low as well (logic 0) and the feedback loop becomes conducting. For the same pulsation of less than 2.5V, the clock output Q. of the flipflop becomes high (logic 1) to provide a signal which is processed by 'monostable chip' 14 and the solid state switch 15 to form an input pulse to the logger which is recorded. Thus one pass of the meter index point 9 across the optical path is recorded.

When the feedback loop conducts, the output voltage signal S from the phototransistor divides into two signals S, and S2 where S1 < S > S2 and S1 + S2 = S in terms of magnitude. S, supplies the Schmitt trigger (part B) 4b while S2 supplies the feedback loop. For example, S = 2.4V whilst S1 = S2 = 1.2V.

The circuit does not reset to its original state until the trigger voltage of 2.5V is applied to the input of Schmitt trigger (part B) 4b. This will only occur when the input voltage to the feedback loop is also 2.5V and this will result only when S1 = S2 = 2.5 so S, + S2 = 5V and that is only when substantially all of the meter index pointer 9 has passed out of the optical path to allow maximum reflection to, and thus output from, the phototransistor 5. Mere vibration of the pointer 9 within the beam will not cause multiple pulsing and recording by the logger after the single recordal of one pass of the pointer as maximum reflection to the phototransistor will not occur, although the phototransistor voltage will vary with the vibration.

Thus, as the pointer leaves the optical path completely tlh circuit returns to its original state as before with the feedback loop in the non-conducting condition. It will be appreciated from the above description that if the pointer vibrates into and out of the optical path either when the circuit is in its original state, or when the circuit is in the state with the feedback loop conducting, the vibration will not cause an undesired input signal to the logger.

It will be understood that whilst a particular enbodiment of the invention has been described, various modifications-may be made without departing from the scope of the invention. For example, instead of a Schmitt trigger the signal processing circuit may include a comparitor and/or an operational amplifier and/or other device which switches from logic 0 to logic 1 and vice versa.

Moreover, the invention is applicable to meters other than gas meters, for example, electricity meters. Also the sensor arrangement may be used to detect and record passes of markers other than a pointer through the optical path. For example, the pass of a spot on the face of a rotating disc or a mark on the circumferencial edge of such a disc.

Claims

1. An electro-optical sensor arrangement for detecting movement of a meter index marker through a light beam comprising a pulse generator connected to a light emitting means, a photo-transducer for receiving light pulses emanating from the light emitting means and providing a pulsed input signal to a signal processing circuit which provides a pulsed output recorded by a recording means when the strength of said pulsed input falls to a predetermined trigger magnitude whereat the circuit is triggered from a first state to a second state to cause a further fall in the strength of the pulsed input, the circuit returning to its first state when the strength of the pulsed input rises to the trigger magnitude whereat the circuit is triggered to cause a further increaser in the pulsed input strength.

2. An electro-optical sensor arrangement as claimed in claim 1 wherein a feedback loop is connected the signal processing circuit, the feedback loop being non-conducting when the circuit is in the first state, becoming conducting when the circuit is triggered to the second state, and remaining conducting until the circuit is triggered back to the first state.

3. An electro-optical sensor arrangement as claimed in claim 2, wherein the feedback loop includes a reverse bias diode and a series resistor.

4. An electro-optical sensor arrangement as claimed in claim 2 or claim 3, wherein the magnitude of the input signal to the signal processing circuit falls by substantially 50% when the feedback loop becomes conducting and increases by substantially 100% when the feedback loop becomes non-conducting.

5. An electro-optical sensor arrangement as claimed in any of the preceding claims, wherein the signal processing circuit includes a Schmitt trigger which receives the input signal.

6. An electro-optical sensor arrangement as claimed in any of the preceding claims, wherein the signal processing circuit includes a comparitor which receives the input signal.

7. An electro-optical sensor arrangement as claimed in any of the preceding claims wherein the signal processing circuit includes an operational amplifier which receives the input signal.

8. An electro-optical sensor arrangement as claimed in claim 1 and substantially as hereinbefore described with reference to the drawings.