GB2101296A - Remote position-monitoring - Google Patents

Abstract

The movements of a pointer (2) of a meter (1) past a specific point around a scale (3) of the meter are monitored by means of a pulsed beam of incident light from an LED source (4) and sensed, after reflection from the scale (3), by a phototransistor (7). As the pointer moves through the light beam, the average amplitude of pulses received by the transducer falls then rises and a trigger pulse is initiated by a level detector (11) when the average amplitude reaches a first threshold (A) during the fall. The trigger pulse is terminated when the average amplitude reaches a second threshold (B) during the subsequent rise. <IMAGE>

Description

SPECIFICATION Remote position monitoring method and apparatus This invention relates to a method for the remote monitoring of the passage of an object past a monitored location (for example the passage of a meter pointer past a desired scale position), and to apparatus for performing the method.

There is often a need to monitor the position of a moving object at a remote location, in such a way that an electrical signal is generated when the object moves past a monitored location. Included in the many examples of such needs may be mentioned the moving indicators of energy consumption meters which are often located in inconvenient positions for regular inspection.

Frequent inspection of an energy consumption meter is one simple way of reducing the possibility of prodigal energy use, energy conservation being of increasing importance in commercial and domestic management with increasing cost of energy.

Energy consumption meters are normally the property of the energy supply organisation and any modifying of such meters to provide a remote monitoring facility is not normally permitted.

Thus satisfactory apparatus for remove monitoring of such meters must be simple to install on a range of different meters without any adaptation of the meters, must work equally well on meters with pointers of different materials, shapes and sizes and, so far as the method is concerned, must be reliable, be able to cope with a wide range of different speeds of movement of the pointer, be able to operate in varying levels of ambient light and be able to work well in the face of backlash on the pointer e.g. in the case of a poorly designed or well-worn meter mechanism. For certain industrial applications, it is desirable that the position monitoring method used be safe in potentially dangerous environments such as at high voltage or in the presence of explosive gas mixtures.

It has been proposed to sense the reflection of "light" (e.g. infra-red radiation) from the pointer as it passes the monitored location but this proposal has inherent problems in that even if a region along the path of the pointer is flooded with high intensity "light", since many pointers are very poor reflectors of the incident "light", the changes in intensity of "light" received by the sensor when the pointer moves through the illuminated region can be little different from the changes occasioned by variations in the ambient lighting conditions.

Further in the prior art proposal, pointer passage is noted by an increase in sensed "light" intensity against a high background level and the electronic circuitry has to be designed to detect such an increase in the face of a varying background level.

According to one aspect of the present invention, a method of monitoring the passage of a moving object past a monitored location comprises projecting an incident beam of electromagnetic radiation onto a reflecting surface, receiving radiation reflected from said incident beam by the surface in an opto-electrical transducer, at least one of said incident beams and the reflected radiation passing through the position occupied by said moving object in the said location, monitoring the electrical output signal from the transducer to determine the presence of a minimum caused by a reduction in the intensity of the reflected radiation by the object in the said location, and producing an electrical output signal in response thereto.

In the case where the object is the pointer of a meter, the reflecting surface can be the scale plate of the meter.

Suitably the incident beam has a wavelength lying in, or close to, the optical part of the electromagnetic spectrum and preferably is a beam of pulses derived from an LED. The optoelectrical transducer can be a photo-transistor.

Desirably the output of the transducer is integrated and fed to a level detector which generates a substantially rectangular pulse, to serve as the output signal, when the object passes the monitored location. The threshold settings for the rise and fall of such a rectangular pulse are conveniently different (for the purpose hereafter described) and may be adjustable with respect to the sensed minimum.

The incident beam is desirably well collimated to give a narrow parallel beam and conveniently the relative dispositions of the incident beam and the reflected radiation are such that no part of the incident beam reflected by the object can affect the transducer.

According to a further aspect of the invention, apparatus for the remote monitoring of the passage of an object past a monitored location comprises, a source of incident electromagnetic radiation and drive means therefor which in use produce an incident beam directed at a reflecting surface beyond the object when in its monitored location, an opto-electrical transducer positioned to receive a lower intensity of reflected incident radiation from said surface when the object is in its monitored location, and electrical circuit means connected to the transducer to produce an electrical output signal in response to a temporary reduction in intensity of reflected incident radiation received by the transducer.

Desirably the drive means and source produce pulses of incident radiation and the circuit means includes an integrator to average the intensity over a plurality of sequential reflected pulses received by the transducer. A memory may be disposed upstream of the integrator to store the amplified output of the transducer and a level detector may be disposed downstream of the integrator to generate the output signal.

The pulse width is desirably a minor part of the interval between two pulses and could be between 10 and 0.1% thereof. The pulse rate can be less than, equal to or greater than mains frequency, but if it is different from mains frequency (e.g. by a non-integral factor), it is possible to eliminate at least a proportion of ambient light effects by electrical filtering.

In a practical embodiment, the components of the apparatus can be housed together in one unit which, for example in the case of a meter pointer sensing device, could be located close to, but not necessarily in contact with, the meter, adjacent to the scale over which the pointer moves, an electrical lead being used to connect the unit to a remote device (e.g. a microprocessor or alarm) employed to respond to the output signals.

The invention will now be further described, by way of example, with reference to the accompanying drawing, the sole Figure of which is a schematic representation of an apparatus for detecting each rotation of a pointer of a meter.

The meter (e.g. a gas meter or a watt-hour meter) is shown schematically at 1 and comprises a rotatable pointer 2 moving over a scale plate 3.

An LED 4 is fed from a pulse generator drive unit 5 and the "light" output from the LED is collimated to a width which is at most a few times that of the width of the illuminated part of the pointer and ideally less than that width. The collimating means is shown schematically at 6 in the drawing.

A photo-transistor 7 (or other suitable optoelectrical transducer) is positioned to receive the LED "light" reflected from the plate 3 but preferably not LED "light" reflected from the pointer 2 in its monitored position.

The output from the transistor 7 will be a series of pulses at the repetition rate of the drive unit 5 and this output is fed into an amplifier 8, whose output feeds a store 9. The store 9 averages the amplitudes of a plurality of the most recent pulses and feeds this average to an integrator 10.

When the pointer 2 moves around its path to approach the monitored position, it will start to obscure the beam of incident LED "light" and also the reflected LED "light" and will thus reduce the amplitude of the pulses fed to (and from) the amplifier 8. The output from the integrator 10 will therefore show a reduction as the pointer approaches the monitored position, reaching a minimum in the monitored position and will increase again as the pointer moves away from the monitored position.

This dip in the output of the integrator 10 is monitored by a level detector 11 which senses a first level (A) on the leading flank of the dip to trigger the start of a rectangular output pulse and senses a second level (B) on the trailing flank of the dip to trigger the end of the output pulse.

The electrical signals which would, in a typical case, appear at the integers 5, 8, 10 and 11 are shown above those integers in the drawing.

The output pulse would be led away by a line 1 2 to an output device at a location remote from the meter 1. The output device has not been shown in the drawing but could be a slave meter, some form of alarm to indicate when a predetermined number of output pulses has been received, or even a control unit (e.g. based on a microprocessor) to modify the performance of equipment powered from the energy supply whose meter is being monitored.

In practice, in a typical energy consumption meter, the drive mechanism of the pointer is of imperfect design or construction and the pointer is unlikely to move smoothly, to move always at the same rate, to move always in the same direction or to be free of "backlash". The apparatus described above can make reliable passage detections even in the face of these unpredictable perturbations in pointer movement.

By using a sufficiently short duration of pulse of LED "light" at a sufficiently fast repetition rate, a fast moving pointer can be detected. In a practical case (and purely by way of example) a pulse duration of 100 ,uses. and a pulse repetition rate of 10 per second could be used. The capacity of the store 9 can be equivalent to a few pulses or a few hundred and can easily be selected to suit the application in question. By storing a number of sequential pulses and integrating the stored value, intermittent movements of the pointer can be compensated for.

"Backlash" can be offset to some extent by making the monitored location one in which backlash is unlikely to be a problem (e.g. in the case of a pointer turning about a horizontal axis by monitoring appreciably to one side or the other of the 12 o'clock - 6 o'clock line) and can be further compensated by setting a substantially higher threshold level for A than for B as discussed above. In this way the pointer can make a substantial false reverse movement after the leading flank of the output pulse has been triggered without triggering the trailing flank of the output pulse.

In practice it has been found convenient to locate the monitored position between the 2 and 4 o'clock positions in the case of a pointer turning about a horizontal axis.

Monitoring a "dip" in the integrator output has advantages since it is electronically easier to detect a dip in a noisy signal and such an arrangement facilitates measurements in ambient lighting conditions subject to considerable changes.

Although use with a meter has been described, it should be appreciated that the position monitoring apparatus and method disclosed herein can be used for other applications where movement of an object past a monitored position needs to be sensed.

Claims (22)

1. A method of monitoring the passage of a moving object past a monitored location which comprises projecting an incident beam of electromagnetic radiation onto a reflecting surface, receiving radiation reflected from said incident beam by the surface in an opto-electrical transducer, at least one of said incident beams and the reflected radiation passing through the position occupied by said moving object in the said location, monitoring the electrical output signal from the transducer to determine the presence of a minimum caused by a reduction in the intensity of the reflected radiation by the object in the said location, and producing an electrical output signal in response thereto.

2. A method as claimed in claim 1, in which the object is the pointer of a meter, and the reflecting surface is the scale plate of the meter.

3. A method as claimed in claim 1 or claim 2, in which the incident beam has a wavelength lying in, or close to, the optical part of the electromagnetic spectrum.

4. A method as claimed in any preceding claim, in which the incident beam is pulsed.

5. A method as claimed in claim 4, in which the pulse width is a minor part of the interval between two adjacent pulses.

6. A method as claimed in claim 5, in which the pulse width is between 10% and 0.1% of the interval between two adjacent pulses.

7. A method as claimed in any of claims 4 to 6, in which the pulse rate is different from mains frequency by a non-integral factor.

8. A method as claimed in any preceding claim in which the output of the transducer is integrated and fed to a level detector which generates a substantially rectangular pulse as its output signal when the object passes the monitored location.

9. A method as claimed in claim 8, in which a first threshold setting of the level detector employed for signalling the rise of the rectangular pulse is different from a second threshold setting of the level detector employed for signalling the fall of said rectangular pulse.

10. A method as claimed in claim 9, in which the first threshold setting is closer to the sensed minimum output of the level detector than is the second threshold setting.

11. A method as claimed in any preceding claim in which the incident beam is collimated to give a narrow parallel beam and the relative dispositions of the incident beam and the reflected radiation are such that no part of the incident beam reflected by the object can affect the transducer.

12. A method as claimed in any preceding claim for monitoring the passage of a meter pointer turning about an axis of the pointer, in which the pointer axis lies in a plane containing the incident beam and the reflected radiation.

13. A method as claimed in any preceding claim, in which the width of the incident beam in the direction of movement of the object is less than the width of the object where it is irradiated by the incident beam also measured in the same direction.

14. A method of monitoring the passage of a meter pointer past a scale plate of the meter substantially as herein described with reference to the accompanying drawing.

15. Apparatus for the remote monitoring of the passage of an object past a monitored location comprising, a source of incident electromagnetic radiation and drive means therefor which in use produce an incident beam directed at a reflecting surface beyond the object when in its monitored location, an opto-electrical transducer positioned to receive a lower intensity of reflected incident radiation from said surface when the object is in its monitored location, and electrical circuit means connected to the transducer to produce an electrical output signal in response to a temporary reduction in intensity of reflected incident radiation received by the transducer.

16. Apparatus according to claim 15, in which the drive means and source produce pulses of incident radiation and the circuit means includes an integrator to average the intensity over a plurality of sequential reflected pulses,received by the transducer.

1 7. Apparatus according to claim 16, in which a memory unit is disposed upstream of the integrator to store the amplified output of the transducer and a level detector is disposed downstream of the integrator to generate the output signal.

1 8. Apparatus according to claim 1 6 or claim 17, in which the pulse width is a minor part of the interval between two pulses and the pulse rate is different from mains frequency by a non-integral factor.

19. Apparatus as claimed in any of claims 1 5 to 18, in which the source of incident radiation is an LED, and the transducer is a photo-transistor.

20. Apparatus as claimed in any preceding claim, in which the components of the apparatus are housed together in one unit which, in the case of a meter pointer sensing device, is adapted to be located close to the meter, adjacent to the scale over which the pointer moves, an electrical lead being used to connect the unit to a remote device employed to respond to the output signals.

21. Apparatus as claimed in claim 20, in which said remote device is a control unit based on a microprocessor to modify the performance of equipment powered from an energy supply which includes the meter as a power supply monitor.

22. Apparatus for detecting each rotation of a pointer of a meter substantially as herein described with reference to the accompanying drawing.