GB1580465A

GB1580465A - Electricity meters

Info

Publication number: GB1580465A
Application number: GB3942577A
Authority: GB
Original assignee: Heliowatt Werke Elektrizitaet GmbH
Current assignee: Heliowatt Werke Elektrizitaet GmbH
Priority date: 1976-09-21
Filing date: 1977-09-21
Publication date: 1980-12-03
Also published as: ATA671677A; CH622102A5; BE858779A; DE2642892B2; DE2642892A1; IT1087712B; FR2365163B1; NL7706956A; IE45872L; LU78125A1; DK376377A; FR2365163A1; IE45872B1

Abstract

In this method, an electronic maximum demand indicator with a computer, preferably a microcomputer (MC), a non-volatile memory (SP), and a display device (A) linked to it is used. Because the number of available inputs and outputs is limited by the components, a multiplex device, which is controlled by the computer (MC), is used, in order to make multiple use of the available connections. Also, different codes are assigned to the individual parts of the circuit, to prevent commands being confused, and so that data lines can be exploited doubly. <IMAGE>

Description

(54) ELECTRICITY METERS (71) We, HELIOWATT WERKE ELEK TRlzlTATs-GEsELLscHAFT mbH., a German company, of Wilmersdorfer Strasse 39, 1000 Berlin 12, Germany (fed rep), do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to maximum-demand electricity meters, for metering the maximum demand which has occured over a preceding predetermined interval.

In a substantially all-electronic maximum demand electricity meter comprising a computer, it is useful to provide a non-volatile store. The main advantage of such a store is to provide a means for storing essential data in the event of a power failure. Such arrangements are disclosed in the following British Applications, 11692/77 (1,524,794); 28626/77 (1,542,814); and 30985/77 (1,539,128). It is desirable to employ a single microcomputer chip, although this will have a limited number of external connections, and such microcomputer chips known to us, at the present time, do not incorporate nonvolatile stores on the same chip. Therefore the number of connections effected between the microcomputer chip and other different circuits of the meter requires to be optimised.

According to the present invention, there is provided a maximum-demand electricity meter comprising an input switching means, a computer and a non-volatile store for storing data in the event of a power supply failure, wherein: the input switching means is arranged to be controlled by the computer to connect thereto selected ones of input signals to the meter; the computer has control and data output lines which are common to different circuits of the meter, the computer being arranged to select by means of control signals which of said circuits is to be controlled via said lines at a given time and to output thereto data in a code suitable for a selected one of the circuits; the non-volatile store is activated via a calling input thereof only when a calling instruction from the computer is present at said calling input simultaneously with a mains failure signal which in a first state indicates that a power supply failure has occurred and in a second state indicates that the power supply has reached an acceptable level; and when the non-volatile store is not activated, it receives from the computer a rest instruction which causes the store to assume a condition in which maximum storage duration is obtained.

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a block circuit diagram of a maximum-demand meter; Figure 2 illustrates one example of the construction of a circuit arrangement of the maximum-demand meter; Figure 3 illustrates one example of an arrangement for inputting data into a nonvolatile store of the meter; and Figure 4 illustrates one example of an input change-over switch for the maximum demand meter.

In the Figures, like component elements are denoted by like references.

As indicated above, a single-chip microcomputer having an integrated non-volatile write and read store is not at present readily available, so that there must be employed for an electronic maximum-demand meter an external non-volatile semiconductor store which must be addressed by the computer, fed with input signals, and read in the same way as any other store. Such an arrangement is illustrated in Figure 1, in which MC denotes the single-chip microcomputer, SP the non-volatile semiconductor store (MNOS), A a digital display unit and M an input change-over switch for the computer. The properties of the individual circuitry parts will first be explained.

The store SP for the maximum demand meter has a storage capacity of 256 bits, it being possible to select with a 6-bit address 64 words each having 4 bits. Also, the store SP has available to it three instruction inputs by which the following states of operation can be determined: (i) Total clearance of all storage cells; (ii) Introduction of an addressed 4-bit word into a buffer store on the switching circuit of the store; (iii) Writing of an addressed block of four 4-bit words from the buffer store of the switching circuit into the MNOS storage cells; and (iv) Reading of an addressed block of four 4-bit words into the buffer store and from there through output lines.

One of the three instruction inputs denoted by CA (Figure 2) is a calling input and serves to call the storage switching circuit; only when a logical "1" signal is present at this input is the switching circuit activated. The outputs of the storage switching circuit have high ohmic impedance and are turned on only at reading.

Owing to the physical properties of the MNOS store transistors no voltages should be present at them in the state of rest, because otherwise the stored charge will be prematurely lost. Therefore, there is applied when the store is in the state of rest an instruction combination which internally causes the switching circuit to take up the preferred state of rest without voltages at the MNOS transistors.

The single-chip microcomputer has available four input lines, eleven output control lines, eight output data lines and one main reset input. The eleven output control lines can only be turned on or off in succession.

The eight output data lines are the outputs of a programmable gate arrangement in the computer switching circuit, i.e. of a so-called "programmable logic array" (PLA), with the aid of which data supplied by the store of the computer in 4-bit binary or BCD code and one data bit from the arithmetic unit can be recoded to the eight output lines.

For example, a code conversion from BCD code into seven-segment code for operation of the display unit is possible by means of the gate arrangement.

The digital display unit A has nine places, of which the first two are used for displaying an identification and the last six for the display of a momentary numerical value.

The identification indicates in each instance what the indicated numerical value means.

The digital display is desirably activated in multiplex operation. Depending upon the construction of the computer switching circuit and the nature of the display, interposed driver states may be necessary. Such digit driver and segment driver states DT, ST are indicated in Figure 1. Since the computer has available only four inputs, there is first provided an electronic input change-over switch M by which, first, the four output lines of the store SP and the input signals for the maximum demand meter are applied to the computer input. In a simple construction of the maximum meter register, the following nine input signals are to be processed.

(a) A signal for turning on and off the maximum demand measurement.

(b) Two signals for the initiation of a so-called monthly resetting, i.e. the transfer of a momentary monthly maximum into a cumulative counter.

(c) 50-Hz mains frequency for time base and other purposes.

(d) A signal from a light-sensitive element on the front plate of the meter instrument behind a reading window. Such signals serve first to turn on the inoperative display unit and then to cause it, by each further signal, to output another value in a normally fixedly preset sequence.

(e) A signal from a further light-sensitive element which is disposed under a light screen behind a sealable aperture in the meter housing and which initiates so-called manual resettling.

(f) One or two signals from a pulse pickup device of a kilowatt-hour meter. In the case of an electronic meter, only one signal is required. In the case of a electro-mechanical Ferraris meter having a rotor disc, two signals may be necessary in order to detect and suppress faulty pulses when the disc is turned back. This is particularly important when the maximum demand meter is provided itself with a kilowatt-hour metering unit whose reading is comparable with the reading of the mechanical kilowatt-hour metering unit in the primary counter, because errors in the pulse pick-up, which need not affect a maximum-demand measurement itself, may lead to considerable differences in the two kilowatt-hour indications in the course of time.

(g) A mains failure signal.

The eleven output control lines of the computer are doubly utilised, in that eight of these lines are connected to the eight places of the digital display unit A and six of these eight lines are simultaneously connected to address inputs of the store SP.

A ninth control output U (Figure 2) is on the one hand connected to the digit driver DT and turns the whole display unit A on or off. At the same time, this control line is fed with a mains failure signal NS, through an AND gate G (inverting or non-inverting), to the instruction input CA of the store SP.

As long as the store input CA is at logical "0", the stored data cannot be influenced by reason of the internal construction of the store SP. Only when the supply voltages are turned on and off may it be necessary to adhere to a particular sequence for avoiding destruction of the data.

The mains failure signal NS comes from the current supply of the maximum demand meter and informs the maximum demand meter of the mains failure in good time to ensure that any necessary write and read operations are safely carried out before the collapse of the supply voltages. After the restoration of the mains supply, the mains failure signal NS again assumes the logical "1" condition only when the supply voltages of the maximum demand register have with certainty reached their nominal values. Since the computer can supply unforeseeable signals at its outputs when the supply voltages are turned on, it is further necessary for the store input CA to be enabled only when the computer has also been brought to a definitive initial condition by way of a main reset input R, so that there cannot appear at the store input CA any parasitic signals which might result in variations of the content of the store. A typical computer requires at least six timing pulse periods for its resetting, for example 30 ss, and automatically effects resetting when the supply voltages are turned on. Before the NS signal and the AND gate G jumps to a logical "1", the computer is reset. In this way, parasitic signals are prevented at the store input CA.

The display unit A requires seven-segment information and a line for the decimal point.

The store SP requires information in BCD code along four lines. The eight output data lines of the computer are doubly utilised, in that, when the display unit is turned on, seven-segment codes are output thereat.

When information is to be written into the store, the programmable gate arrangement (PLA) in the computer is so switched under program control that data in BCD code for the store is then taken from four of the eight available lines.

The supply of the eight input signals of the maximum demand meter and of the four output signals of the store SP to the existing four inputs of the computer takes place by means of the multi-pole input change-over switch M.

An embodiment which has been constructed in practice and which is particularly advantageous is illustrated in Figure 2. The inputs of the computer require incorporated MOS resistances to zero potential. The input change-over switch M is available in two versions. Its outputs can either be switched with high ohmic impedance, or they can be forced to zero potential by a corresponding control instruction, independently of the input signals present. As mentioned, the outputs of the store SP are basically of high ohmic impedance and are turned on only in the-read operation. The outputs of the input change-over switch M and of the store SP can then be directly connected together and connected to the input of the computer MC. Should the outputs of the input changeover switch M only be adapted to be specifically switched to zero potential, unidirectional conducting elements, for example diodes D, are required in the output lines.

Four of the eight available data outputs of the computer are also applied to the store SP. Of the eleven control outputs of the computer, eight are again applied to the digit driver DT for activating the individual places of the display unit. Six of these are also connected to the store SP. The switching line denoted by U leads to the digit driver DT for turning on and off the display unit and through the AND gate G with the mains failure signal NS to the instruction input CA of the store SP.

In the distribution of the remaining control connections of the computer, it is further taken into account that the non-volatile semiconductor store SP requires a preferred instruction combination for the so-called parking operation when in the state of rest with supply voltages present. The two instruction inputs B and C cannot simultaneously be used for other purposes because otherwise the store SP would continuously be internally changed over. Accordingly, these inputs B and C are activated by two control lines of the computer which are intended specifically for this purpose.

The input change-over switch M is controlled by those two of the eight address lines of the digit driver which are not simultaneously intended also for the store SP.

In this way, the reading of the input signal of the maximum demand register is coupled in time with the calling of particular digits of the display, but this is of no importance and is taken into consideration in the program. When the store SP is addressed for the purpose of reading, it must at the same time be ensured that the input change-over switch M emits no signals. Therefore, the other control lines used as address lines cannot be utilised for turning off the input change-over switch.

It is of no importance if, during operation of the store SP, the display unit A briefly indicates meaningless symbols which are imperceptible to the human eye. The only exception is an erasing operation, which lasts about 1 s. Because the store SP requires the calling signal CA during this time, the display is automatically turned off during this time owing to the coupling, indicated in Figure 2, with the digit driver DT controlling the display.

The storage time of a MNOS store is temperature-dependent. The power loss in such a PMOS/MNOS switching circuit is relatively great and results in considerable self-heating which has a detrimental effect on the storage time.

With such non-volatile stores having limited storage time, use is made of the principle of refreshment at sufficiently frequent intervals. In this way, the storage time in normal operation substantially loses its importance, because the duration of a mains failure is almost invariably shorter than the storage time of such a switching circuit.

Also, the power loss is then eliminated.

Owing to the limited storage capacity in a single-chip microcomputer, the refreshment of the MNOS store preferably takes place block-wise, i.e. only individual regions of the store are read out for refreshment and re-written at any one time. The refreshment is further desirably coupled with the write-in of new data. If, for example, the stored value for a monthly maximum is changed, other storage locations are than refreshed in the same erase and write operation. In this way, account is also taken of the limited useful life of such MNOS stores, which is limited mainly by the erasing operations.

If it is desirable for particular applications to limit the storage value in normal operation of the meter between two refreshments, then the supply voltages of the MNOS store are turned on only when the store is actually required. At the same time, the current supply is thereby relieved of load and the heat balance of the instrument is enhanced.

Since conventional Bakelite (R.T.M.) housings are preferably employed for electronic maximum counters, the dissipation of loss heat produced always constitutes a problem, especially when an electronic maximum demand meter is combined with a Ferraris meter which already gives off considerable loss heat. When the supply voltages are turned off, the remaining terminal connecting members of the store SP also receive no further signals, and in this case they are desirably isolated by corresponding switching means.

The user-related programming of the electronic maximum-demand meter can take place by writing of corresponding values into the non-volatile store. In the simplest case, the storage block is fed with userrelated data externally of the meter and then introduced into the maximum-demand meter.

Alternatively, this data could be written into the meter itself. For this purpose, each input and output of the store SP is preceded by a resistance, as shown in Figure 3. A programming unit is so connected by means of a suitable plug-in device that its lines are directly connected to the terminal connecting members of the store SP. For programming, corresponding signals are applied to the store under low-impedance conditions by the programming unit, independently of what signals are applied by other parts of the maximum demand register through the resistances. In order to prevent disturbances from arising at the instant of the connection or disconnection of the programming unit, the computer MC is preferably stopped for a sufficient time by way of its main reset input.

In a further development of the invention, the input change-over switch M is provided with a corresponding number of additional inputs, so that the programming unit can be connected thereto. The write-in of desired data into the store SP then takes place with the aid of a computer program provided therefor. For checking the written-in userrelated data, the latter must either be fed back to the programming unit in order to be compared and/or indicated therein, or may be controllably displayed at any time at the display unit A of the maximum demand meter.

As stated at the beginning, nine signals are typically applied to such a maximum demand meter. However, conventional input change-over switches only have available four, eight or sixteen inputs. Therefore, input signals may be so combined before the input change-over switch M that the existing number of inputs of the latter is sufficient.

For example, two inputs are provided for the separately-controlled monthly resetting, while a third input would have to be present for the so-called manual reset triggered at the instrument itself. The monthly reset is conventionally triggered by the change-over contact of a centralised-control receiver, so that only one of the two inputs provided for this purpose may be in the logical "1" state at any one time. The state in which the two inputs are at logical "0" is also permitted.

The state in which the two inputs are at logical "1", however, cannot occur as a practical combination, and this state can therefore be used in accordance for triggering the manual reset, in that the triggering element present in the unit, when actuated, brings the two monthly reset inputs with precedence into the logical "1" state. In order to distinguish between disturbances along the line leading from the centralisedcontrol receiver to the maximum demand meter and an intentional manual reset, the two imputs are so read under program control that a manual reset is recognised as such only when the signal provided therefor is uninterruptedly present at least for a predetermined time.

Some of the signals applied to the maximum demand meter, such as the 50 Hz sinusoidal voltage from the mains supply, and the signals obtained by sensing the revolutions of the rotor of a Ferraris meter, can be processed by the computer only when they have been converted into completely satisfactory digital signals. Therefore, a CMOS switching circuit can be employed as the input change-over switch M. With a CMOS switching circuit, the input threshold voltage, once present, remains substantially constant, and in addition a conventional CMOS switching circuit displays a high amplification factor, so that even signals differing from square-wave form are converted into square-wave signals with high edge steepnesses. However, problems may arise by virtue of the internal structure of a CMOS switching circuit. If the linear range of a CMOS switching circuit is passed through too slowly, the switching circuit may emit parasitic signals, for example in the form of oscillations. In order to suppress these, there is employed an input changeover switch M whose input comprises bistable storage elements. If such a switching circuit is available, the unambiguous bistable behaviour can be obtained by connecting resistors R1 in series with the inputs by way of resistors R2 to the inputs, as illustrated in Figure 4. The positive feedback thereby produced makes the corresponding inputs behave as a Schmitt trigger.

WHAT WE CLAIM IS:- 1. A maximum-demand electricity meter comprising an input switching means, a computer and a non-volatile store for storing data in the event of a power supply failure, wherein: the input switching means is arranged to be controlled by the computer to connect thereto selected ones of input signals to the meter; the computer has control and data output lines which are common to different circuits of the meter, the computer being arranged to select by means of control signals which of said circuits is to be controlled via said lines at a given time and to output thereto data in a code suitable for a selected one of the circuits; the non-volatile store is activated via a calling input thereof only when a calling instruction from the computer is present at said calling input simultaneously with a mains failure signal which in a first state indicates that a power supply failure has occurred and in a second state indicates that the power supply has reached an acceptable level; and when the non-volatile store is not activated, it receives from the computer a rest instruction which causes the store to assume a condition in which maximum storage duration is obtained.

2. A meter according to claim 1, wherein the computer has an output specifically for providing said rest instruction.

3. A meter according to claim 1 or 2, wherein said rest instruction comprises a preset combination of instruction signals.

4. A meter according to claim 1, 2 or 3, further comprising a preset combination of instruction signals.

5. A meter according to any preceding claim, wherein said switching means comprises an input change-over switch whose outputs can be switched on and off by suitable control instructions under high-impedance conditions, the outputs of the nonvolatile store are adapted to be switched under high-impedance conditions and are connected to the outputs of the input changeover switch either directly or through unidirectional conducting elements, and the outputs of the non-volatile store are connected to data inputs of the computer.

6. A meter according to claim 4 or to claims 4 and 5, wherein eight data output lines of the computer are connected to the indicating device either directly or by way of a segment driver; seven of said data output lines output the data in seven-segment code, while the eighth line switches the decimal point; and four of said eight data output lines are also supplied to data inputs of the non-volatile store, the data being output along these four lines from the computer in BCD code when they are intended for the store.

7. A meter according to claim 5 or 6, wherein the computer controls the indicating device through nine control lines fed to a digit driver, eight of said nine lines serving for calling individual digit places in multiplex operation, while the ninth line is intended for turning on and off the whole display and is also connected via an AND gate to said calling input of the store, which gate is also connected to receive said mains failure signal; in use, each time the store is called, the display unit (A) is turned off and vice versa; and six of the eight control lines of the computer which are intended for controlling the digit places of the indicating device are connected also to address inputs of the store, the computer indicating to the store along these six lines in each instance the address of a desired storage location, the remaining two of the eight control lines being connected to control inputs of the input changeover switch through which the input changeover switch (M) is turned off whenever the store is read.

8. A meter according to any preceding claim, wherein the computer comprises a device which, when the supply voltage of the computer is turned on, automatically triggers a main reset which sets the computer in a defined initial condition.

9. A meter according to any preceding

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. satisfactory digital signals. Therefore, a CMOS switching circuit can be employed as the input change-over switch M. With a CMOS switching circuit, the input threshold voltage, once present, remains substantially constant, and in addition a conventional CMOS switching circuit displays a high amplification factor, so that even signals differing from square-wave form are converted into square-wave signals with high edge steepnesses. However, problems may arise by virtue of the internal structure of a CMOS switching circuit. If the linear range of a CMOS switching circuit is passed through too slowly, the switching circuit may emit parasitic signals, for example in the form of oscillations. In order to suppress these, there is employed an input changeover switch M whose input comprises bistable storage elements. If such a switching circuit is available, the unambiguous bistable behaviour can be obtained by connecting resistors R1 in series with the inputs by way of resistors R2 to the inputs, as illustrated in Figure 4. The positive feedback thereby produced makes the corresponding inputs behave as a Schmitt trigger. WHAT WE CLAIM IS:-

1. A maximum-demand electricity meter comprising an input switching means, a computer and a non-volatile store for storing data in the event of a power supply failure, wherein: the input switching means is arranged to be controlled by the computer to connect thereto selected ones of input signals to the meter; the computer has control and data output lines which are common to different circuits of the meter, the computer being arranged to select by means of control signals which of said circuits is to be controlled via said lines at a given time and to output thereto data in a code suitable for a selected one of the circuits; the non-volatile store is activated via a calling input thereof only when a calling instruction from the computer is present at said calling input simultaneously with a mains failure signal which in a first state indicates that a power supply failure has occurred and in a second state indicates that the power supply has reached an acceptable level; and when the non-volatile store is not activated, it receives from the computer a rest instruction which causes the store to assume a condition in which maximum storage duration is obtained.

9. A meter according to any preceding

claim, wherein the computer comprises means such as a programmable gate arrangement or programmable logic array, on the input side of its data outputs, by means of which the coding of output data can be changed over under program control.

10. A meter according to any preceding claim, wherein the computer has control outputs having storage capacity which can be independently called, and any desired bit combination of these control outputs can be produced and stored under program control.

11. A meter according to any preceding claim, wherein the computer is arranged to periodically refresh the content of the nonvolatile store blockwise, refreshment being coupled with the write-in of new data, such that a particular number of storage locations are refreshed simultaneously with each erase and write operation performed.

12. A meter according to any preceding claim, wherein, in use, a supply voltage to the non-volatile store is turned on only when the store is actually required, and there is provided means for preventing signals from being applied to the switching circuit of the store when turned off.

13. A meter according to any preceding claim, wherein supply voltages to the nonvolatile store are arranged to be turned on and off in a predetermined sequence.

14. A meter according to any preceding claim, wherein the write-in of such data which serves for user-relates programming of the maximum-demand meter takes place externally of the meter with a suitable programming unit, and the circuit thus programmed is therefore introduced into the meter.

15. A meter according to any preceding claim, wherein a resistor is connected in series with each input and each output of the store, and there are provided connections for a programming unit, which connections lead directly to the switching circuit of the store.

16. A meter according to any preceding claim, wherein the computer is arranged to be stopped by way of its main reset input before connection of a programming unit thereto, and is arranged to restart again only after disconnection of the programming unit.

17. A meter according to any preceding claim, wherein all the inputs and outputs of the store are connected to those circuitry parts of the meter which are adapted to be switched under high impedance conditions by suitable control instructions.

18. A meter according to any preceding claim, including a programming unit which, when connected to the store, monitors instruction inputs of the store and commences programming thereof only when any store operations which happen to be proceeding are terminated; and wherein a resetting of the computer or a disconnection of other circuitry parts of the meter depends upon the state of the instruction inputs of the store.

19. A meter according to any preceding claim, wherein user-related programming of the meter is applied to the latter through corresponding inputs of the input switching means and written into the store with the aid of a corresponding program of the computer.

20. A meter according to claim 4 or to any one of claims 5 to 19 as appendant thereto, including a programming unit, and wherein user-related data written into the store is returned for monitoring to the programming unit and/or indicated or displayed on the indicating device of the maximum demand meter itself.

21. A meter according to any preceding claim, wherein, for reducing the number of inputs to the input switching means, means is provided for combining input signals of the maximum demand meter before they are applied to the inputs of the input switching means.

22. A meter according to any preceding claim, wherein, for the purpose of triggering so-called manual resetting of the meter, two inputs of the input switching means which are provided for separately controlled monthly resetting are brought into a predetermined logical state, and there is provided a computer program which, on recognition of the corresponding bit combination, tests whether the combination is uninteruptedly present at least for a predetermined time before a manual resetting is triggered.

23. A meter according to any preceding claim, wherein the input switching means is a CMOS switching circuit which performs the function of appropriately re-shaping input signals which are present in other than square-wave form.

24. A meter according to any preceding claim, wherein input circuits of the input switching means comprises bistable circuits.

25. A meter according to any preceding claim, wherein each input of the input switching means is preceded by a resistor and resistors lead directly back from the outputs to the associated inputs, and the positive feedback thereby produced thus imparts Schmitt-trigger behaviour to the inputs which are respectively turned on.

26. A maximum-demand electricity meter substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.

27. A maximum-demand electricity meter substantially as hereinbefore described with reference to Figures 1 and 2, Figures 1 to 3, or Figures 1 to 4 of the accompanying drawings.