GB2146782A

GB2146782A - Device for counting the revolutions of a rotating body

Info

Publication number: GB2146782A
Application number: GB08419421A
Authority: GB
Inventors: Eduard Baumann
Original assignee: Zellweger Uster AG
Current assignee: Zellweger Uster AG
Priority date: 1983-09-15
Filing date: 1984-07-30
Publication date: 1985-04-24
Also published as: AU572426B2; CH664019A5; GB2146782B; ZA845937B; DE3422172C2; DE3422172A1; GB8419421D0; AU3166384A

Abstract

Arrangement for use, in particular, in counting the revolutions of the rotor disc (5) of an electricity meter, comprises a marker (17) on the disc, and at least one electrode (18) located on the path on which the marker (17) moves. The capacitance variations occurring as the marker (17) rotates past the electrode (18) are used for counting the revolutions of the rotor 16 disc (5). Strontium titanate may be used as the marker. The electrode (18) is located on a component (22) which is clamped to the first plate of the meter, and which possesses all the necessary electrical connections (19, 21). The device is particularly suitable for converting single-tariff meters to multiple-tariff operation. <IMAGE>

Description

SPECIFICATION Device for counting the revolutions of a rotating body The invention relates to a device for counting the revolutions of a rotating body, in particular of a rotor disc of an electricity meter, it being possible to drive this motor disc by means of a field which is generated by the load current and the supply voltage.

In known electricity meters, the device for counting the revolutions of the rotor disc is formed by installing a worm on the rotor shaft carrying the rotor, this worm meshing with a gearwheel which drives a counter via further gearwheels. When using electricity meters of this type, as soon as there is a requirement that the information regarding the number of rotor-disc revolutions should be available not only in the meter itself, but also at another place, namely that the information must be transmitted electrically, the meters must be equipped with additional devices.

It is possible to obtain electricity meters possessing one or more control contacts which open and close in proportion to the number of rotor-disc revolutions, thereby making available the signals needed for the electrical transmission of the desired information.

However, if a meter does not have these control contacts, it is impossible to equip it with them subsequently, at its point of installation. This retro-fitting operation had rather, to be performed at a central location. However, it was then necessary to connect a substitute meter for the duration of the conversion, and fhis could not be justified in economic terms, on account of the high costs.

In addition, electricity meters have already been proposed, in which the counting of the rotor-disc revolutions is effected by an electrooptical method. It would, admittedly, be possible to design optical scanning devices such that they could be installed in an existing meter, in situ, with comparatively little difficulty. However, they cannot be considered, because the lives of the photocells and photodiodes which are currently obtainable are at least one order of magnitude shorter than the period of time over which an electricity meter must ran without maintenance, and without breaking down.

An object of the invention, is to propose a device for counting the rotor-disc revolutions which, on the one hand, supplies the information regarding the number of rotor-disc revolutions in the form of electrical signals, and which, on the other hand, has a sufficiently long useful life, amounting, for example, to ten or twenty years.

According to the invention, there is provided a device for counting the revolutions of a rotating body in particular of a rotor disc of an electricity meter, it being possible to drive this rotor disc by means of a field which is generated by the load current and the supply voltage, characterised in that the rotor disc is provided with a marker which possesses a dielectric constant differing from that of air, in that at least one electrode is located on the path on which the marker moves, and in that a means for counting the revolutions of the rotor disc is presented by the variation in the capacitance of the electrode, relative to its surroundings, occurring whenever the rotating marker passes it.

The capacitative rotor-disc scanning element, according to the invention, supplies the information regarding the number of rotor-disc revolutions in the form of electrical signals which can be transmitted and evaluated in any desired manner, and represents, without doubt, a low-cost solution, while the life requirements can be met without any difficulty.

In a preferred further development of the device according to the invention, the electrode is located on a component which can be fastened to the electricity meter.

In a preferred embodiment of the device according to the invention a second electrode is provided, which is formed by the rotor disc, the electrical connection to the rotor disc being made via the rotor shaft and a rubbing contact which bears against this shaft and is carried by the abovementioned component.

In a further embodiment of the device according to the invention, a plurality of electrodes, preferably three electrodes, are located on the component, in a plane which is parallel to that of the rotor disc.

According to a further development of these two preferred embodiments of the device according to the invention, the component carrying the electrodes is clamped to the electricity meter, preferably to its front plate, and possesses the necessary electrical connections for the electrodes.

A device for counting the rotor-disc revolutions, designed in this manner, thus consists only of a single component, which is clamped to the meter and, on the one hand, carries a plurality of electrodes, or only one, and the rubbing contact, and which, on the other hand, possesses the necessary electrical connections. In addition, the marker must be applied to the rotor disc, it being possible to perform this operation by attaching a thin platelet of some appropriate material, using an adhesive, or by dabbing-on a small drop of some suitable liquid which solidifies once having been dabbed-on. It is obvious that these two operations-the clamping of the component and the application of the marker---can be peformed quickly and easily, and involve virtually no interference with the electricity meter.

A device which has been designed in the abovementioned manner is accordingly suitable, to an outstanding degree for converting meters which are already in existence and have already been installed. This is of considerable economic importance for example, in changing-over from a single tariff to multiple tariffs. As is commonly known, the so-called multiple-tariff meters possess a plurality of counters, to which the measuring movement is selectively coupled, by means of a time switch, or by means of a ripple control receiver, so that electricity drawn at different times can be charged separately. Hitherto, it has been impossible to convert a single-tariff meter to multiple tariffs in an economic manner, so that, up to the present, changing over to multiple tariffs has involved replacing the old meters by new ones.

The device according to the invention now enables, for the first time, a conversion of the abovementioned kind to be performed without difficulty, in that an authorised service employee attaches the component to the meter, and applies the marker to the rotor disc.

Since, as a rule, the multiple tariff in any case necessitates a ripple control receiver, the evaluating unit for the device is best integrated with the ripple control receiver, to form one apparatus which then contains, in particular, one of more counters, for example one for the high tariff and one for the low tariff. The counter which the meter originally contained would then indicate the total electricity consumption, while the high-tariff and low-tariff consumptions would be indicated by the two counters in the apparatus containing the ripple control receiver.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows a front view, in perspective, of an electricity meter with a capacitative scanning device, according to the invention, for countering the revolutions of the rotor disc, the front plate of the meter having been removed; Figure 2 shows a detail of the meter depicted in Figure 1 looking towards the front plate from the rear in a perspective representation; Figure 3 shows a diagrammatic representation of one variant of the scanning device shown in Figure 1; Figure 4 shows a diagrammatic representation of another variant of the scanning device shown in Figure 1;; Figure 5 shows a block circuit diagram of an evaluating unit for the scanning device shown in Figure 1, and Figures 6 and 7 each show a block circuit diagram of an evaluating unit for the scanning device shown in Figure 3, and/or in Figure 4.

Figures 1 and 2 depict an electricity meter of the conventional type, together with its most important constituent parts. Here, Figure 1 shows a front view of the meter, with the front plate removed, while Figure 2 shows a view from the interior of the meter, looking towards the front plate, the drawing included only the parts which are necessary for understanding the capacitative scanning device As represented, the meter consists of a baseplate 1, on which a so-called rotor shaft 4 is mounted, vertically, in upper and lower bearings, 2 and 3 respectively, in a manner such that it can rotate freely. The rotor shaft 4 carries a horizontal disc 5, the so-called rotor disc, which rotates, together with the rotor shaft 4, when current is drawn from the mains supply N, the number of rotations of the rotor disc 5 representing a measure of the quantity of electricity consumed.In the region of the rotor disc 5, the baseplate 1 possesses a slot-iike cut-out 6 which contains the rotor disc 5 and enables a portion of it to pass through the baseplate 1.

The rotor disc 5 is driven, in a known manner, by means of two electro-magnets, the iron-cored current coil 7, through which the load current flows, and the iron-cored voltage coil 8, to which the supply voltage is applied, these coils generating, as a result of their arrangement, a moving magnetic field.

As a result of induction, this moving field gives rise to eddy currents in the rotor disc 5, generating a torque which is proportional to the product of the two magnetic fields. At the same time, the rotor disc 5 passes through the field of a permanent magnet 9, this field generating likewise by induction, a retarding torque which is proportional to the speed of the rotor disc 5. The number of rotations of the rotor disc 5 corresponds to the power which has been drawn from the mains supply N.

The rotor shaft 4 is provided with a worm 10 with which a gearwheel 11 meshes, this gearwheel drivng a counter 1 2 via further gearwheels. These further gearwheels are not represented, and the mechanism for driving the counter 12, which is generally located in the region of the upper portion of the front plate 1 3 (Figure 2) is symbolished by a broken line 14, running between the shaft 15, carrying the gearwheel 11 and the counter 12.

As Figure 1 shows, a plurality of attachment arms 16, for the front plate 1 3 (Figure 2), are machined on the baseplate 1, four being shown in this particular representation, the front plate 1 3 being fastened to them by means of screws. In this regard, it is unimportant as to whether the front plate 1 3 is composed of two portions, as shown in Figure 2, or whether it consists of only one part. It is essential, in all cases, that it should possess a slot for enabling the front edge of the rotor disc 5, as referred to Figure 1, to pass through.

The parts of the electricity meter represented in the Figures, described up to this point, are known, and correspond to those of a conventional single-tariff meter. It is now intended to show how this single-tariff meter can be converted to a multiple-tariff meter.

For this purpose the invention proposes that a capacitative scanning device be installed, the purpose of which is to count the revolutions of the rotor disc 5. This capacitative scanning device is formed by applying a marker 1 7 to the rotor disc 5, this marker being composed of a material which possesses a dielectric constant differing from that of air, and by detecting and counting the variations in the capacitance between two connections, 19 and 21, arising as the rotating marker 1 7 passes an electrode 18, these variations consequently being used as a means for counting the revolutions of the rotor disc 5.

As shown in the Figures the marker 1 7 is applied to the underside of the rotor disc 5, in the region of its edge. The size of the marker 1 7 approximates to that represented in the Figures, namely a few square millimeters, and is so small that the running behaviour and the accuracy of movement of the rotor disc 5 are not impaired. The shape of the marker 1 7 is unimportant, and could also be, for example, circular. The application of the marker 17, to the rotor disc 5, can be effected by attaching a small, thin platelet, or a piece of film, using an adhesive, or also, for example, by dabbingon or spraying-on a drop of suitable liquid which solidifies once having been applied.

Strontium titanate has, for example, proved to be a suitable material for the marker 17, this compound possessing a dielectric constant in excess of 100.

A small, conducting plate 1 8 is located beneath the rotor disc 5, with a suitable clearance of approximately 1 mm, on the path on which the marker 1 7 moves, this small plate 1 8 forming one of the electrodes of a measuring capacitor and being connected to a connection 1 9. The other electrode of the capacitor is formed by the surroundings of the small plate 1 8 principally the rotor disc 5, which is electrically connected to a connection 21, via the rotor shaft 4 and a rubbing contact 20 which bears against this shaft.Due to the fact that the marker 1 7 possesses a dielectric constant differing from that of air, the capacitance which can be measured between the connections 19 and 21 when the rotor disc 5 has rotated to the position shown in the figures, at which the marker 1 7 is just moving past the small plate 18, is different from that which can be measured when the rotor disc 5 has rotated to the other positions, when the marker 1 7 is distant from the small plate 1 8. Since the changed capacitance value occurs whenever the marker 1 7 rotates past the small plate 18, that is to say once on each revolution of the rotor disc 5, this capacitance variation can be used for counting the revolutions of the rotor disc 5.

The small plate 1 8 and the rubbing contact 20 are fastened to a common component 22.

This component 22 is provided with a fastening-clip 23 by means of which it is clamped to the lower portion of the front plate 1 3. In order to convert a single-tariff meter to multiple tariffs, the service employee, for example, an installation technician belonging to the electricity undertaking responsible for the supply, needs merely to apply the marker 1 7 to the rotor disc 5, and then to push the clip 23 of the component 22 over the lower edge of the front plate 23. The component 22 possesses the necessary electrical connections, 19 and 21, which are preferably combined to form a common cable.This cable is led out of the meter at a suitable point, so that the only remaining operation which the service technician might possibly have to perform with the aid of a tool would be to drill a hole in the meter case, for leading this cable through. The conversion of the meter consequently involves no interference of any kind, with its active portion and requires no speical knowledge or skills on the part of the service technicial, who can perform the converion easily and quickly, at the point of installation of the meter.

Even although the capacitative scanning device is presented, in Figures 1 and 2, in the context of the conversion of a single-tariff meter to multiple tariffs, the capacitative scanning device is, of course, not restricted to this application. This also applies in the case of the illustrative embodiments shown in Figures 3 and 4. This is because it is advantageous, in the production of new electricity meters as well , to install capacitative scanning devices in them, replacing the worm 10, the gearwheel 11, and the further gearwheels.

In the case of the illustrative embodiment of the capacitative scanning device represented in Figure 3, the rotor disc 5 does not form one of the electrodes of the measuring capacitor, since a total of three electrodes, 24,25 and 26, are located beneath the rotor disc 5, in the configuration shown in the Figure, so that the rubbing contact 20 (Figure 1) is dispensed with.

When, as the rotor disc 5 rotates in the direction marked by an arrow, the marker 1 7 reaches the electrodes, it first sweeps across the electrode 25 and one half of the electrode 24, after which it sweeps across the electrode 26 and the other half of the electrode 24.

During this process, the resulting variations in the capacitances at the connections 27, 28 and 29 of the electrodes 24, 25 and 26 are as follows. As soon as the marker 1 7 sweeps across the electrode 25, and one half of the electrode 24, and capacitance between these electrodes, and hence between their connections 28 and 27, rises and falls back to the initial value after the marker 1 7 has moved past the electrode 25. When the marker 1 7 sweeps across the electrode 26, and the other half of the electrode 24, the capacitance between these electrodes, and hence between their connections 29 and 27, rises and falls back to the initial value after the marker 1 7 has passed the electrode 26.These capacitance variations, occurring once on each revolution of the rotor disc 5, can now be used, in the same way, for counting the rotor-disc revolutions.

By shortening its length in the radial direction, the marker 1 7 could be arranged to continue to sweep across the electrodes 25 and 26, but not to sweep across the electrode 24. This modification would not bring about any change in the capacitance-variation process which has been described.

Figure 4 shows another configuration of the three electrodes 24 25 and 26, according to which they are arranged in a row, the marker 1 7 sweeping across only the electrode 25 as the rotor disc 5 rotates. As a result, only the capacitance between the connections 27 and 28 rises as the marker 1 7 rotates past the electrodes, and not that between the connections 28 and 29. Since these different capacitances, between the connections 27 and 28 on the one hand and between the connections 27 and 29 on the other, occur only once per rotor-disc revolution, they can likewise be used for counting the revolutions of the rotor disc 5.

In the cases of the illustrative embodiments shown in Figures 3 and 4, the electrodes 24, 25 and 26 are also, of course, located on a common component which can be fastened to the meter as a retrospective addition, for example, in the manner of the component 22 shown in Figure 1.

Figure 5 shows the block circuit diagram of an evaluating unit for the capacitative scanning device represented in Figure 1. In Figure 5, it is assumed that an alternating voltage is present at the two electrodes of the capacitor, namely at the rotor disc 5 and at the small plate 1 8. The capacitance between the connections 19 and 21 (Figure 1) is used as a constituent of the frequency-determining elements, of an oscillator 30, which then oscillates at different frequencies corresponding to the two different capacitances of,the capacitor, depending on whether the marker 1 7 is just sweeping across the small plate 1 8 (Figure 1), or not.In this context, let f0 denote the frequency of the oscillator 30 corresponding to the smaller capacitance, and f denote the frequency corresponding to the larger capacitance. A filter 31, or another frequency-discriminating element, tuned to the frequency f, is connected in series with the oscillator 30, the output from this filter, or other frequencydiscriminating element, being led, via a rectifier 32, to a terminal 33.

As long as the oscillator 30 oscillates vt the frequency f., the output voltage at the terminal 33 will be very low If however. the oscillator 30 oscillates at the frequency f, the output voltage U at the terminal 33 will rise to an appreciably higher value. This highervalue output voltage will consequently occur, at the terminal 33, whenever the marker 1 7 is just sweeping across the small plate 18, and can accordingly be used for driving a meter Figure 6 shows the block circuit diagram of an evaluating unit for a capacitative scanning device of the type displayed in Figure 3 or Figure 4, this evaluating unit possessing a bridge circuit, the input terminals of which are connected to the connections 27, 28 and 29 of the capacitative scanning device.The two electrodes, 24 and 25, possessing the connections 27 and 28 are symbolised by a capacitor K,. drawn with a broken line, while the two electrodes, 24 and 26, possessing the connections 27 and 29 are symbolised by a capacitor K2, likewise drawn with a broken line.

As long as the marker 1 7 is not sweeping across the electrodes 24, 25 and 26, the capacitances between the connections 27 and 28 , on the one side, and between the connections 27 and 29, on the other, are equal, and the symmetrically-constructed bridge, its central arm containing an oscillator 38, oscillating at the frequency fO, is in balance, and its output voltage U, between the terminals 34 and 35, is zero. When the marker 1 7 approaches the electrodes 24 and 25, the capacitance between the connections 27 and 28 rises, causing the bridge to go out of tune. This signifies that the voltage at point 37 rises, relative to the voltage at point 36, so that the terminal 35 becomes positive in relation to the terminal 34.When, following the maximum overlap with the electrodes 24 and 25, the marker 1 7 recedes from the latter electrode, and approaches the electrode 26, the bridge returns to the balanced condition, with zero output voltage. When subsequently, the marker 1 7 comes to overlap the second half of the electrode 24, and the electrode 26, the other arm of the bridge is caused to go out of tune. Since the capacitance between the connections 27 and 29 now attains a higher value, the voltage at point 36 rises, so that the terminal 34 becomes positive in relation to the terminal 35. These polarity reversals occur once on each revolution of the rotor disc, and can accordingly be used to actuate a meter which counts the rotor-disc revolutions Those bridge-circuit components which have not been specifically mentioned here, such as the rectifiers, capacitors, and resistors, are assumed to fall within the understanding of a person skilled in the art, and are not provided with reference numbers in the Figure.

The bridge circuit shown in Figure 6 can also be used as the evaluating unit for the capacitative scanning device represented in Figure 4. Since, with this arrangement, the marker 1 7 sweeps over only the electrode 25, only the right-hand arm of the bridge would, in this case, be caused to go out of tune, and the terminal 35 would become positive in relation to the terminal 34. This would also result in the delivery of a voltage pulse between the terminals 34 and 35, by means of which the rotor-disc revolutions could be counted.

The electrode arrangements shown in Figures 3 and 4 have the advantage that the assembly distance between the electrodes 24, 25 and 26 on the one hand, and the rotor disc 5 (Figure 1) on the other hand, is comparatively uncritical, these electrodes being grouped in order to form a mechnical module.

This insensitivity reflects the fact that, in the case of these arrangements, the capacitances between the electrode 24 and the electrodes 25 and 26, respectively, vary in the same manner with the distance to the rotor disc 5, so that a change in the assembly distance does not cause the bridge to go out of tune.

For the same reason, distance changes caused by temperature fluctuations or ageing also fail to influence the counting of the rotor disc 5.

Figure 7 shows an evaluating unit which can be used in place of the bridge circuit represented in Figure 6. As shown, this unit comprises two oscillators 39 and 40, a mixer stage 41, and a high-pass filter 42 the output terminal of this filter being connected, via a rectifier 43, to an output terminal 44.

As in the case of the illustrative embodiment represented in Figure 5, the capacitance between the connections 27 and 29 is used as a constituent of the frequency-determining elements of the oscillator 39, while that between the connections 27 and 28 is similarly used in respect of the oscillator 40. As long as the marker 1 7 is distant from the electrodes 24, 25 and 26 (Figures 3 and 4), the capacitances between the abovementioned connections are equal, and the two oscillators, 39 and 40, operate at the same frequency, fO.

As a result, the mixer stage 41 delivers a directcurrent signal at its output terminal, which cannot pass through the high-pass filter 42.

When the marker 1 7 moves over the electrodes 25 (Figure 4), the capacitance between the connections 27 and 29 rises, and the oscillator 39 alters its frequency. The difference frequency of the two oscillators, 39 and 40, then appears at the output terminal of the mixer stage 41, this difference frequency being able to pass through the high-pass filter 42 and, via the rectifier 43, generating a voltage U at the output terminal 44. In this way, it is possible to achieve very sensitive detection, exhibiting high stability by virtue of the symmetrical construction of the evaluating unit.

When multiple-tariff meters are employed, switching-over between the individual types of tariff is effected by means of a remote-control system based on ripple control receivers.

When, therefore, a single-tariff meter is to be converted to multiple tariffs (Figures 1 and 2) the conversion necessitates the installation of a ripple control receiver in the vicinity of the electricity meter. It is advantageous to integrate, into this ripple control receiver, the evaluating unit for the capacitative scanning device, together with the necessary additional meter, it being essential, of course, to provide more than one additional meter if more than two types of tariff are involved. In operation, a multiple-tariff meter, converted as described above, counts the normal-tariff electricity consumption by means of the mechanical counter which is present in the meter, and displays the corresponding readings. The control pulse for another tariff, supplied by the ripple control receiver, then brings the capacitative scanning device into operation, and assigns the counting pulses, output by the evaluating unit, to the appropriate meter.

On switching over to the normal tariff, the ripple control receiver then switches off the capacitative scanning device again.

Claims

1. A device for counting the revolutions of a rotating body in particular of a rotor disc of an electricity meter, it being possible to drive this rotor disc by means of a field which is generated by the load current and the supply voltage, characterised in that the rotor disc is provided with a marker which possesses a dielectric constant differing from that of air, in that at least one electrode is located on the path on which the marker moves, and in that a means for counting the revolutions of the rotor disc is presented by the variation in the capacitance of the electrode, relative to its surroundings, occurring whenever the rotating marker passes it.

2. A device according the Claim 1, characterised in that the electrode is located on a component which can be fastened to the electricity meter.

3. A device according to Claim 2, characterised in that a further electrode is provided, which is formed by the rotor disc, the electrical connection to the rotor disc being made via the rotor shaft and a rubbing contact which bears against this shaft and is carried by said component.

4. A device according to Claim 2 or 3 characterised in that a plurality of electrodes are located on the component in a plane which is parallel to that of the rotor disc.

5. A device according to Claim 4, characterised in that three electrodes are located on the component.

6. A device according to Claim 5, characterised in that the first and second of said three electrodes are located one behind the other, in the direction in which the rotor disc rotates, in that the third electrode is offset relative to the first and second electrodes, in a radial direction on the rotor disc, and in that at least the first and second electrodes lie on the path on which the marker moves.

7. A device according to Claim 5, characterised in that said three electrodes are located side by side, in a radial direction on the rotor disc and in that only the first or second electrodes lies on the path on which the marker moves.

8. A device according to one of Claim 3 to 7, characterised in that the component carrying the electrodes is clamped to the electricity meter, preferably to its front plate, and possesses the nesessary electrical connections for the electrodes.

9. A device according to any of Claims 3 to 8 for the purpose of converting a single-tariff meter to multiple-tariff operation, this meter possessing a measuring movement and a counter which is driven thereby, characterised in that connections for the electrodes are connected to an evaluating unit which is located outside the meter and which can be switched on and off by means of a control, preferably by means of a ripple control receiver, this evaluating unit possessing an additional counter for each additional type of tariff, and being integrated with the ripple control receiver in order to form a combined apparatus.

10. A device according to Claim 9 when dependent on Claim 3 characterised in that the evaluating unit possesses an oscillator which is connected to the connections of the electrodes, a frequency-discriminating element, preferably a filter, which is connected in series with the oscillator, a rectifier which is connected in series with the filter, and a terminal which is connected in series with the rectifier, the output voltage at this terminal serving as the control voltage for the additional counter, or counters, in that the capacitance between the electrode connections forms a constituent of the frequency-determining elements of the oscillator, and in that the frequency-discriminating element is tuned to the oscillator frequency corresponding to the relatively higher capacitance between the electrode connections.

11. A device according to Claim 8 when dependent on Claim 4, 5 or 6 characterised in that the evaluating unit possesses a symmetrically-constructed bridge circuit, of which the common, central arm is connected to the connection of the third electrode, while its two other arms are connected to the connections of the first and second electrodes, and in that the polarity-alternations of the voltage which is obtainable at the bridge-circuit output terminals, serve to actuate the additional counter, or counters.

12. A device according to Claim 8 when dependent on Claim 4, 5 or 6 characterised in that the evaluating unit possesses two oscillators which are connected to the connections of the electrodes, a mixer stage which is connected in series with the oscillators, a filter which is connected in series with the mixer stage, a rectifier which is connected in series with the filter, and a terminal which is connected in series with the rectifier, the output voltage at this terminal serving as the control voltage for the additional counter, or counters, in that each oscillator is connected to the first electrode or to the second electrode as well as to the third electrode in that the capacitances between the corresponding electrode connections form a constituent of the frequencydeterming elements of the oscillator, and in that the filter is tuned to the difference frequency of the two oscillators which appears at the output terminal of the mixer stage.

13. A device for counting the revolutions of a rotating body substantially as herein described with reference to Figures 1 and 2 with or without reference to any of Figures 3 to 7 of the accompanying drawings.

14. An electricity meter comprising a device according to any proceeding claim.