OF A ROTATING COMPONENT

This invention relates to an apparatus for, and a method of, counting the revolutions of a rotating component and is especially, though not exclusively, concerned with counting

the revolutions of a Ferraris disc of an electricity consumption registering meter.

In the field of electricity consumption registering meters, remote meter reading is desirable and it is known to provide an optical-pick up to detect rotation of the Ferraris disc of an electricity consumption registering meter by directing light onto the disc and detecting light reflected from it. Rotation of the disc causes a mark on the disc to modulate the reflected light due to the variation in reflectance of the disc. The optical pick-up is arranged produce a signal which has a peak, or trough, in its magnitude each time the mark passes the optical pick-up. The optical pick-up feeds the signal to circuitry which counts the number of peaks, which corresponds to the number of rotations of the disc, and calculates the amount of electricity consumed. To detect the peaks it is known to use a magnitude threshold level which, when exceeded by the signal magnitude, indicates that one rotation of the disc has occurred. Some electricity consumption registering meters, however, have more than one mark on their edge which

results in the optical pick-up falsely over-reading the number of rotations ofthe disc. As a result each optical pick-up has to be manually programmed with the number of marks for the individual meter which is time consuming and expensive. In addition to intentionally applied marks, some discs may have other marks such as scratches or dirt

on their edge which results in the optical pick-up over-reading the number of rotations of the disc. The inventors have realised that a need exists, therefore, for an apparatus

and/or a method which can automatically determine the number of marks on the disc.

According to the invention there is provided apparatus for counting the revolutions of a rotating component, comprising means for generating a signal having features which correspond to marks on the component and means for utilising said signal to determine

the number of marks on the disc. Conveniently the features are peaks or troughs in the

variation of the magnitude ofthe signal with time.

In one embodiment the means for utilising comprises means for matching features in the signal to determine two features which are generated by the same mark and means for providing an output representing the number of marks to be one more than the number of features between said two features. Conveniently the features are peaks or troughs in the variation of the magnitude of the signal with time.

Conveniently the means for matching comprises means for comparing one value of a selected parameter of the signal with other values of the selected parameter of the signal until a said other value is found which is substantially equal to the said one value.

In a preferred embodiment of the invention the means for matching further comprises means for comparing a value adjacent in time to said one value with a value which is correspondingly adjacent to said other value to determine whether said adjacent values

are substantially equal.

Conveniently the selected parameter is the time period between successive said features in the signal. Alternatively the selected parameter is the magnitude of the signal features, which enables the number of marks to be determined when the marks are

equally spaced on the component or when the component is not rotating at a constant rate.

In one particular application ofthe invention the rotating component comprises a Ferraris disc of an electricity consumption registering meter. In such an application the means for generating the signal conveniently comprises an optical pick-up which comprises a light source arranged to direct light onto the rotating component and a photodetector to receive reflected light therefrom.

According to another aspect of the invention a method of counting the revolutions of a rotating component comprises; generating a signal having features which correspond to marks on the component; matching features in the signal to determine two features which are generated by the

same mark; and counting the number of features between two said features; and

calculating the number of marks to be one more than the number of features between two said features.

Conveniently the method of matching the features comprises comparing one value of a selected parameter ofthe signal with other values ofthe selected parameter ofthe signal

until a said other value is found which is substantially equal to the said one value.

In a preferred embodiment the method further comprises comparing a value adjacent in time to said one value with a value which is correspondingly adjacent to said other value

to determine whether said adjacent values are substantially equal. Such a method gives

a greater level of confidence in the accuracy ofthe method.

Conveniently the selected parameter is the time period between successive said features in the signal. Alternatively the selected parameter is the magnitude of the signal features or the average signal magnitude between signal features or other statistical parameter of the signal.

An apparatus and a method in accordance with the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a block schematic diagram ofthe apparatus;

Figure 2 is a plot of input signal magnitude versus time for the apparatus for a disc which has four marks;

Figure 3 is a plot of input signal magnitude versus time for the apparatus for a disc which has three equally spaced marks; and

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Figure 4 is a further plot of input signal magnitude versus time for the apparatus.

Referring to Figure 1, there is shown a Ferraris disc 1 of an electricity consumption registering meter. On an edge 2 of the disc 1 there are a plurality of marks 3. The disc

1 rotates in a direction as indicated by arrow 4.

The apparatus includes an optical pick-up 5 which is arranged to generate a signal 10 which is related to rotation of the disc 1. The optical pick up 5 comprises a light source 6 which is arranged to direct light 7 onto the edge 2 of the disc 1 and a photodetector 8 to detect light 9 reflected from the edge 2. Rotation of the disc 1 causes the marks 3 to modulate the light 9 reaching the photodetector 8 such that the photodetector 8 produces a signal 10 whose magnitude cyclically varies with time due to variations in the reflectance of the edge of the disc 1. The signal 10 is applied to an input of an analogue to digital (A/D) converter 12 which samples and digitises the signal 10 to produce a sequence of digital data sample values. A microprocessor 13 connected to the A/D converter 12 processes these digital data sample values to determine the number of marks 3 on the edge 2 of the disc 1 using any of a number of alternative methods now described.

Referring to Figure 2 there is shown a typical plot of signal magnitude versus time for a disc 1 which has four marks 3 on its edge 2. Respective peaks 20 to 29 in the signal magnitude occur as the four marks 3 pass the optical pick-up 5. During determination

of the number of marks, the disc 1 is rotated at a constant rate, for example by applying a constant load to the supply monitored by the electricity meter.

The microprocessor 13 detects the peaks 20 to 29 using a magnitude level threshold V _ft ,

the peak being taken to have occurred when the signal magnitude exceeds the threshold

V _th . The processor 13 is arranged to measure the time intervals, t , to t g, between the peaks, 20 to 29, and to store these values in a memory 14 (see Figure 1).

The processor 13 uses these time intervals t . to 1 ₉ to match up peaks corresponding to the same mark using the following method. The processor 13 compares a first time interval, for example t , though any time interval can be selected, with the subsequent time interval 1 ₂ to determine if they are equal within a predetermined time limit, for example if they are equal to each other within 1 %. If the time interval 1 ₂ is not equal to t . within the predetermined time limit the processor 13 compares t , with the next time interval, 1 ₃ , to see if these time intervals are equal within the predetermined time limit. If 1 ₃ is not equal to t _λ within the predetermined time limit, the processor 13 compares t j with the next time interval t ₄ . The processor 13 continues this process of comparing time intervals until it finds a further time interval that is equal within the predetermined time limit to the first time interval. Accordingly in the example illustrated in Figure 2 when

the processor 13 compares the interval t . with the fifth time interval t ₅ they are found to

be equal within the predetermined time limit indicating that the peaks 20 and 24 correspond to the same mark. The processor 13 counts the number of time intervals between the equal time intervals, t , and 1 ₅ , in the example, three. The processor 13

calculates the number of marks to be one more than the number of time intervals between

equal time intervals; therefore for the example shown in Figure 2 the processor 13

determines that the disc 1 has four marks 3 on it.

It will be appreciated that this method works only if the same mark 3 produces peaks 20

and 24. If this is the case then the second time interval t ₂ will equal the time interval 1 ₆ . Likewise 1 ₃ will equal 1 ₇ and 1 ₄ equal 1 ₈ . In a preferred embodiment having identified t _: as equal to t , and determined the number of marks, the processor 13 then compares 1 ₂ and 1 ₆ , 1 ₃ and 1 ₇ , and 1 ₄ and 1 ₈ to ensure that they are also equal within the predetermined time limit to give a greater confidence in the result.

Whilst the method described with reference to Figure 2 is found to work well with most discs, it does rely on the disc rotating at a constant rate which is not always possible to achieve. It is also possible that the disc 1 could have a number of marks 3 which are equally spaced around the circumference of the disc 1 so that the time intervals between the peaks resulting from the different marks would be equal. An alternative method to overcome these difficulties will now be described with reference to Figure 3. Figure 3 shows a plot of signal magnitude versus time for a disc 1 which has three equally spaced marks 3 around its edge. As can be seen from the Figure, the time intervals t ₁₀ to t ₁₄

between peaks 30 to 35 are equal, indicating that the disc is rotating at a constant rate, though the alternative method applies equally in the case when the disc is not rotating at a constant rate. In the alternative method the processor 13 is arranged to measure the magnitude of each peak 30 to 35, V . to V ₆ and compares the magnitudes to see if they

are equal within a predetermined magnitude limit.

In the example illustrated in Figure 3, the processor 13 compares the magnitude V jof

peak 30 with the magnitude V ₂ of peak 31 to determine if they are within predetermined

magnitude limit. If V ₁ is not equal to V ₂ within the predetermined magnitude limit this indicates that the peaks 30 and 31 do not result from the same mark and the processor 13 then compares the magnitude V , of peak 30 with the magnitude V ₃ of the next peak

32. If the peaks are not equal within the predetermined magnitude limit, the processor

13 then compares the magnitude of peak with the magnitude V ₄ of the next peak. The processor 13 continues this procedure of comparing the magnitudes of the peaks until it finds a peak of equal magnitude within the predetermined magnitude limit. Accordingly in the example illustrated in Figure 3, when the processor 13 compares the magnitude V _j of peak 30 with the magnitude V ₄ of peak 33 they are found to be equal within the predetermined magnitude limit indicating that peaks 30 and 33 correspond to the same mark. Having found two peaks of equal magnitude, the processor 13 counts the number of peaks between the peaks of equal magnitude to determine the number of marks, which is equal to one more than the number of peaks. In the example illustrated two peaks occur between the peaks corresponding to the same mark, indicating that the

disc has three marks on it. It will be appreciated that this method will still work even

when the disc is not rotating at a constant rate.

Referring to Figure 4, in a further method the processor 13 is configured to match peaks corresponding to the same mark using other parameters ofthe signal 10, for example, the

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average, or mean, signal magnitude between peaks, V _AV , the minimum V-^ or maximum

V _MAX signal magnitude between peaks, the statistical variance or other statistical

parameter of the signal data sample values between peaks. In fact it will be appreciated that it is within the scope of the invention to use values corresponding to almost any parameter of the signal to match peaks corresponding to the same mark. Furthermore it will be appreciated that a combination of methods could be used to give a greater confidence in the result. For example, the peaks could initially be matched using the

time period between peaks and then matched using the magnitude of peaks to ensure that the marks are not equally spaced.

Of course variations may be made without departing from the scope of the present invention. Thus, whilst in the description peaks in the signal magnitude are matched, other features in the signal could be used provided they correspond to marks on the disc. For example, troughs in the signal magnitude or a distinctive pattern in the variation of the signal magnitude may be used. Equally the features could be peaks, troughs or a distinctive pattern in variation of the signal frequency or the signal wavelength.

It will be appreciated that whilst the examples described have been directed to determining the number of marks on a Ferraris disc of an electricity consumption registering meter the invention is suited to determining the number of marks on any form

of rotating component, for example a cyclometer register wheel of a commodity consumption meter.

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Furthermore it will be appreciated that the invention is applicable whether the marks

have been deUberately applied to the disc or are unintentionally applied, i.e. are scratches

or dirt on the disc edge. Hence the invention is applicable even when no intentional

marks have been applied to the disc.

Furthermore the invention is not restricted to a signal which is generated using an optical

pick-up and other means for generating the signal can be used; for example an

electromagnetic or electrostatic sensor.

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