GB2257522A - Utility meters - Google Patents

Abstract

An electrical signal in the form of a pulse for each unit of consumption measured, for example, by a water meter, is provided by means of a pulse generator comprising intermittently-powered solid-state magnetic sensors adjacent a rotating multiple-pole ring magnet. The sensors are arranged in an arc around the rotation axis and utilise a 'jitter' elimination circuit, a simple form of which is shown in Figure 3b, to latch the output 551 from one sensor by means of the output 552 of a second sensor. The pulse generator output may be recorded by known types of electronics registers, counters or pulse loggers. Spurious pulses arising from the magnet stopping or hovering at a sensor switching point are avoided, as are disadvantages of existing systems e.g. high power consumption, short switch life, or fragile mechanical parts. A number of more sophisticated latching circuits are described. <IMAGE>

Description

UTILITY METERS This invention relates to utility meters and in particular to obtaining electrical output from utility meters for data processing and analysis purposes.

There is an increasing requirement to provide an electrical signal which is a measure of the quantity of the utility being measured. The electrical signal can be used in various ways, for example to provide an electrical input to an electronics unit where the accumulated or tabulated (measurand verses time) amount of the utility is stored for accessing through a display, to a portable data collecting unit as described in our Patent Specification GB 2 229 834A, and/or through a communication link.

Many existing utility meters include a multiple pole ring magnet which rotates at a rate proportional to the quantity of the utility that has passed through the meter. For example, the Kent Meters Helix 2000 range of water meters have a magnet w.hich.rotates at a rate of 1 revolution per 100 litres (meters below 100 mm in diamter) of water flow.

Currently "Optical" or "Reed Switch"' based electrical pulse generators are available for use with these type of utility meters. These systems use a mechanical assembly magnetically coupled, using a second multiple pole ring magnet, to the meter's magnet. The rotation of the magnet in the meter is coupled to rotate either a disk with a number of magnets fitted to it, or a disk with radial lines or markings. The rotation of these disks is then sensed in some units by means of a reed switch operated by the nominally-equally spaced magnets, or in the optical type by sensing the passing of the radial lines through a light emitter/receiver arrangement.

Essentially there are a number of draw-backs with most of the existing units. The optical units require relatively large amount of power for their operation, and the reed/ magnet based models suffer from the relatively short operating life of the reed switch. In addition both models rely on mechanical assemblies to transform the meters rotation to rotation of an optical disk or rotation of many magnets. These mechanical moving parts need to be light weight (in order to reduce load on the meter) and capable of rotating relatively fast. They are therefore, fragile and can be easily damaged due to harsh environment or handling.

According to one aspect of the invention there is provided a utility meter assembly comprising a multiple pole ring magnet which rotates in response to the consumption of a utility, in which electrical pulses for the measurement of utility consumption are derived from the rotation of the ring magnet by means of a solid state pulse generator comprising at least two solid-state magnetic sensors positioned adjacent to the ring magnet and angularly spaced from one another about the axis of the ring magnet, the sensors being powered intermittently, and the outputs of the sensors being sampled by latching means.

The latching means is preferably a D-type latch.

According to a second aspect of the invention, there is provided a utility meter assembly comprising a multiple pole ring magnet which rotates in response to the consumption of a utility, in which electrical pulses for the measurement of utility consumption are derived from the rotation of the ring magnet by means of a solid state pulse, generator comprising at least two solid-state magnet sensors positioned adjacent to the ring magnet and angularly spaced from one another about the axis of the ring magnet, the output from one of the sensors in a stable switching condition being latched by means of the first transition of the output from another of the sensors which may be in an unstable switching condition.

According to a third aspect of the invention, there is provided a utility meter assembly comprising a multiple pole ring magnet in which electrical pulses for the measurement of utility consumption are derived from the rotation of the ring magnet by means of a solid-state generator comprising at least two solid-state magnetic sensors powered intermittently, the outputs of the sensors being sampled and held by first latching means, and the sampled output of a sensor in a stable switching condition from the first latching means, is latched by further latching means using the first transition of the output from a sensor which may be in an unstable switching condition.

The solid-state magnetic sensors are sensors such as Hall Effect Integrated Switches, Linear Hall Effect Integrated Circuits, Magneto-resistive Sensors, Ferrite Cores.

The electrical pulses produced by the solid-state pulse generator are suitable for input to many existing electronics registers, counters or pulse loggers.

Preferably electronic signal conditioning, sensor compensation and sensor redundancy techniques are used (in particular together with multiple Hall Effect Integrated sensors) to achieve a reliable, low power solid-state pulse generating unit for the utility meters.

The number of sensors in such a solid-state pulse generator is a function of 1 - Number of pole pairs on the meter's multiple pole ring magnet.2 - Required resolution in the measured utility (i.e.

number of pulses per amount of utility flow through the meter) 3 - Sensor redundancy level required to reduce jitter, and noise in the pulse generator.

The invention also comprises a pulse generating unit adapted to be mounted on a utility meter, which meter comprises a multiple pole ring magnet rotatable in response to the consumption of a utility, to form a utility meter assembly in accordance with the first, second or third aspects of the invention.

The sensors are preferably all arranged within an arc of substantially no more than 1800. For example five sensors are arranged in one embodiment at angles of 36 degrees apart throughout an arc of 1800.

In a preferred arrangement in accordance with the first and second aspects of the invention, in which there are at least three such sensors, the first rising edge from each sampled sensor (SSn) signal output is applied to the latching means to latch a high level on the respective output, and that latched output is then held until the arrival of the first rising edge from a sensor (SSn+2) positioned two sensors away from the first mentioned (SSn) sensor, that is two sensors angularly behind the first-mentioned sensor (sun), the rising edge of said latter sensor output (SSn+2) being arranged to clear the latching means.

In a preferred arrangement in accordance with the third aspect of the invention, the signal clearing the SSn latch isa momentary pulse generated by the leading edge of the 55no1 sensor signal.

By way of example, specific embodiments of the invention will now be described with reference to the accompanying drawings, in which Figure la shows a scheme for sensor power saving and signal sampling.

Figure lb is a timing diagram for a scheme in accordance with that of Figure la.

Figure 2a is a timing diagram relating edge detection to an ideal sampled output from a single bi-polar Hall Effect sensor in use with a 2-pole ring magnet.

Figure 2b is a timing diagram for an arrangement as in Figure 2a, but in which the sensor is subject to "jitter".

Figure 3a is a timing diagram showing sensor outputs for an arrangement as for Figure 2a but in which a second sensor is positioned at 900 with respect to the first, and in which both sensors are subject to "jitter".

Figure 3b is a circuit which achieves a "jitter-free" output from a sensor arrangement such as for Figure 3a.

Figure 4a is a timing diagram for a sensor arrangement giving rise to unequal "mark"/"space" ratio outputs.

Figure 4b is a circuit which achieves "jitter-free" outputs from a sensor arrangement such as in Figure 4a.

Figure 5 is a circuit which achieves "jitter-free" outputs from a sensor arrangefient' such as in Figures 4a, but gives no output in response to reverse flow of the utility.

A single Hall Effect sensor positioned correctly above a 2n-pole meter magnet (n is the number of pole pairs) would provide 'n' pulses for every revolution of the magnet.

These 'n' pulses provide the electronics circuitry with a total of '2 x n' edges ('n' rising and 'n' falling edges).

If the pulse detector is required to provide 'X' pulses per revolution of the meter' s magnet, and if the sensors output is fed to an edge detector (turning every edge into a short output pulse), then it can be seen that in theory 'X/2n' sensor outputs should be combined to achieve the desired pulses per revolution.

In the case of Hall Effect switches, we propose a minimum of 100% sensor redundancy. This means that rather than 'X/2n' sensors we propose to use 'X/n' sensors or more.

The 100% extra data from the sensors is not passed out by the pulse generator electronics circuitry. These are used together with structural compensation (described below) to achieve the level of compensation required for "jitter-free" operation of the invention.

Standard Hall Effect switches generally incorporate some hysteresis which is achieved from threshhold detection on the integrated circuit. This hysteresis means that a switch may operate at a field strength of 'g' Gauss, but it does not release unless the field strength falls below 'g-h' Gauss, with 'h' being the hysteresis. This hysteresis relies for its operation on the integrated sensor being permanently powered (i.e. in order to remember the previous state of the switch).

In our invention in order to achieve low power consumption, we are using a power pulsing and output sampling technique with the Hall Effect sensors.

This means that the sensors are powered only for relatively short time and are turned off in between the sample periods. The invention therefore can not rely on the in-built hysteresis of the sensors to achieve jitter-free operation.

Figure 1 shows an schematic of the power pulsing and signal sampling used, together with the timing diagram for the scheme.

In order to achieve jitter-free operation two elements of the invention are used.

These are: 1- redundant sensor data (discussed above), and 2- structural sensor positioning.

In theory with a 2-pole ring magnet and a single bi-polar hall effect device one pulse (2 edges) per revolution of the magnet can be obtained, Figure 2a.

However during operation the flow of a utility may stop or slow down to a negligible amount. This means that the magnet may stop at any position in respect to the sensors. If the magnet stops at a position corresponding to the sensor operate and release points, then in a pulse powered system the sensor output can oscillate between 'on' and 'off' states on consecutive application of power pulses. This oscillation can be due to electrical or mechanical noise in the system. Figure 2b shows a single sensor output with 'jitter' and the resulting erroneous edge detector output.

If a second sensor is positioned at 90 degrees with respect to the first, then the position of change of state of the first sensor corresponds to the maximum magnetic field (most stable sensor condition) seen by .the second sensor.

Conversely, the change of state in the output of the second sensor would correspond to the most stable output state of the first. Figure 3a illustrates this 'ideal' phase relationship between sensor 1 output and the output of a 2nd sensor positioned 90 degrees to it (behind in respect to direction of magnetic field revolutions).

From figure 3a, it can be seen that if the transitions of the 2nd sensor output (SS2) are used to 'latch' the output of the 1st (SS1) on a D-type flip-flop, then a 'jitter' free output can be obtained. This simplest form of the 'jitter' elimination is shown in Figure 3b. This circuit operates satisfactorily in all situations when the optimum sensor positioning angle for jitter elimination (this is a function of number of magnetic pole pairs) is large (over 60 degrees). At this simplest level two sensors are used to produce one pulse per revolution.

This in comparison with the theoretical edge detection scheme on a single sensor represents 100% sensor redundancy, and 100% data redundancy (i.e.

400% overall redundancy). This 400% redundancy may be reduced when the number of sensors in a sensor assembly increases, due to the fact that each of the sensors may be used to clock the data from one other in the assembly.

In general however, the combined sensor and data redundancy can not fall below 100% if complete 'jitter' elimination is to be ensured.

In most implementations of this invention both the number of sensors, and the number of magnetic pole pairs, will be higher than two in order to obtain higher number of pulses per revolution. In a typical scenario, 5 sensors will be used to obtain 10 pulses per revolution from a 4 pole (2 pole pairs) ring magnet.

With a 2n-pole ring magnet and 'S' number of bi-polar hall effect sensors, the optimum inter-sensor positioning angle to achieve the highest level of pulse output linearity is given by'360/(n x S)' degrees.

The optimum angle between a sensor and the one confirming its output is given by '1 8O/2n' for a uniformly spaced '2n' pole ring magnet.

Our experiments have shown that significant variations in the phase relationship of the outputs of the sensors can be seen. These variations are due to differences in the characteristics of the sensors, the effect of temperature, errors in positioning of the sensors and the relative strength of the magnetic poles. As can be seen in the Figure 4a, it is possible for the 'mark' to 'space' ratio on the sensor outputs to be other than 1:1. All these variations, when the positioning angle between the sensors is less than 45 degrees, can lead to a situation in which the simple 'Jitter' elimination of figure 3b may not be sufficient Figure 4a, shows the situation in which clocking of the data from sensor 1 by the sensor 2 output will result a permanent 'low' level on the output (missing pulses).

In our experiments, the only reliable characteristic observed in the relationship between the output of the sensors is that, "the rising edge of the 1st sensor output leads the rising edge of the 2nd sensor output".

In the typical scenario of 5 sensors and 2 magnetic pole pairs, the optimum positioning angle to achieve highest linearity is 36 degrees. For optimum 1witter' elimination each sensor output should be clocked with the output from another positioned at 45 degrees. In this situation the 9 degree miss-positioning on 'litter' elimination is of little significance, since even at 45 degrees, the 'mark' to 'space' variations shown in figure 4a can cause missing pulses.

To avoid this missing pulse problem, the circuit of Figure 4b can be used. In this circuit the first rising edge from each Sampled Sensor (SS ) signal output is used to latch a 'highs level on the output. Further ' 'jitter' on leading or trailing transition of that sensor output has no effect on the latched output as they all clock a 'high to an already' 'high1 output.This latched output is then held (stretched) until the arrival of the first rising edge from a sensor positioned at 72 degrees behind (SS +2)' On the arrival of this rising edge the output from ehe initial sensor is removed, and the first latch is held in "clear' (no response to possible jitter) until the arrival of the leading edge of the output positioned at 144 degrees behind (SSn+4). This circuit in theory provides each sensor with a 'jitter' elimination window which stretches from the time of the arrival of the sensors first transition to 144 degrees of revolution.

Note: In the 4 pole, 5 sensor situation described above, the sequence of the pole angle relationships is cyclic with a period of 180 degrees. This means that while SS1 leads SS5 by 144 degrees, it lags behind it by 36 degrees. Therefore, the (n) subscripts above should be operated on in modulo 5 (i.e. SS6 is SSi, 887 is SS2, etc.).

The circuit of figure 4b is general purpose and can be used in different systems with different number of sensors and poles on the magnet. The main requirement for correct operation of a system designed around the circuit, is that the 'Jitter' elimination window on each sensor should stretch beyond the half cycle (90 degrees in the above) and be shorter than the full cycle (180 degrees). There are some situations such as 4-sensor with a 2-pole magnet, when it is not possible to achieve both optimum linearity (90 degree positioning) and acceptable 'jitter' elimination window (optimum 270). In these situations extra (redundant in terms of the system output) sensors should be included in the system to achieve the desired 'jitter' elimination window.

One aspect of the design given in figure 4b is that the system produces some pulses (2.5 pulses per revolution) if the flow of the utility is reversed (reverse revolution of the magnet). In some situations this may be unacceptable. In these cases the design shown in figures 5 can be used. In this circuit the signal clearing the SSn latch is a momentary pulse, generated by the leading edge of the Sun 1 sensor signal. The theoretical 'jitter' elemination window for each sensor is still the required 144 degrees, since the pulse from each sensor is maintained for 144 degrees of revolution. This pulse stretching ensures that at the time of the arrival of SSn+ signal, the state of the previous sensor signal is maintained.Therefore, the missing pulse scenario can not arise, and as can be seen, the latched signal from SSn sensor is delivered to the output stage on the arrival of SS',+i sensor output.

Hence, in the forward direction: 1- Latch 'n' is cleared on the arrival of SS,,1 signal 2- Latch 'n' state is delivered to the output circuit on the arrival of the SSn+l signal.

Therefore, if at any time (say after the arrival of SSn) the flow reverses, the expected next signal (SSn+l) to clock the latch 'n' state to the output will not arrive. Instead, the previous (SSn~l) signal will arrive which will clear latch 'n' and ensure-no pulse is passed to the output stage.

A further embodiment of the invention, not illustrated, involves the possible duplication of the mechanism shown in Figure 5, with the same sampled sensor signals connected to the input latches in the reverse order (SSg connected to latch 1, SS4 to latch 2, ...). This will result in a bi-polar pulse generator, which has two output connections and produces a fixed number of pulses per revolution on one of the two outputs when the utility flows in the forward direction. This bi-polar unit is then capable of producing the same number of pulses per revolution on its other output connection if the flow reverses.

Claims (11)

1. A utility meter assembly comprising a multiple pole ring magnet which rotates in response to the consumption of a utility, in which electrical pulses for the measurement of utility consumption are derived from the rotation of the ring magnet by means of a solid-state pulse generator comprising at least two solid-state magnetic sensors positioned adjacent to the ring magnet and angularly spaced from one another about the axis of the ring magnet, the sensors being powered intermittently, and the outputs of the sensors being sampled by latching means.

2. A utility meter assembly.comprising a multiple pole ring magnet which rotates in response to the consumption of a utility, in which electrical pulses for the measurement of utility consumption are derived from the rotation of the ring magnet by means of a solid-state pulse generator comprising at least two solid-state magnet sensors positioned adjacent to the ring magnet and angularly spaced from one another about the axis of the ring magnet, the output from one of the sensors in a stable switching condition being sampled by latching means on the first transition of the output from another of the sensors which may be in an unstable switching condition.

3. A utility meter assembly as claimed in claim 1 or 2 in which there are at least three sensors, the first rising edge from each sampled sensor (SSn) signal output is applied to the latching means to latch a high level on the respective output, and that latched output is then held until the arrival of the first rising edge from a sensor (sun+2) positioned two sensors away from the first mentioned (sun) sensor, that is two sensors angularly behind the first-mentioned sensor tSSn), the rising edge of said latter sensor output (SSn+2) being arranged to clear the latching means.

4. A utility meter assembly comprising a multiple pole ring magnet in which electrical pulses for the measurement of utility consumption are derived from the rotation of the ring magnet by means of a solidstate generator comprising at least two solid-state magnetic sensors powered intermittently, the outputs of the sensors being sampled and held by first latching means, and the sampled output from the first latching means of a sensor in a stable switching condition is latched by further latching means using the first transition of the output from a sensor which may be in an unstable switching condition.

5. A utility meter assembly as claimed in claim 4 in which the signal clearing an SSn n latch is a momentary pulse generated by the leading edge of an n-l sensor signal.

6. A utility meter assembly as claimed in any one of the preceding claims in which the sensors are all arranged within an arc of no more than substantially 180O.

7. A utility meter assembly as claimed in any one of the preceding claims in which the latching means is D-type.

8. A utility meter assembly substantially as described herein with reference to Figures la, lb, 2a, 2b, 3a, 3b, 4a and 4b of the drawings.

9. A utility meter assembly substantially as described herein with reference to Figures la, lb, 2a, 2b, 3a, 3b, 4a and 5 of the drawings.

10. A bi-polar pulse generator substantially as described herein.

11. A pulse generating unit adapted to be mounted on a utility meter, which meter comprises a multiple pole ring magnet rotatable in response to the consumption of a utility, to form a utility meter assembly as claimed in any one of the preceding claims.