WO1997044679A1

WO1997044679A1 - Meter accuracy device

Info

Publication number: WO1997044679A1
Application number: PCT/NZ1997/000064
Authority: WO
Inventors: Kai Bang Charles Liu
Original assignee: Southpower Limited
Priority date: 1996-05-20
Filing date: 1997-05-20
Publication date: 1997-11-27
Also published as: AU2917297A

Abstract

A device (2) for monitoring the accuracy of an electricity meter (8) which includes a meter interface (3), a central processing unit (4), and a load sensor (7). The load sensor senses changes in loads (9) metered and the processing unit, with appropriate programming and data, compares this load change against a present load change for each load. The acceptable value of any variation in the change of any load can also be preset and the device (2) arranged so that the meter owner is alerted to any unacceptable variation in the accuracy of the meter (8).

Description

TITLE: METER ACCURACY DEVICE

FIELD OF THE INVENTION

The present invention relates to a device for monitoring the accuracy of electricity meters. It may also be used for the detection of electricity meter tampering.

BACKGROUND OF THE INVENTION

Currently available methods of detecting electricity meter tampering involve indicating if the meter has been disabled; for example, the method disclosed in US Patent No. 5422565. However this method cannot detect tampering without disconnection of the meter, which involves interfering with the accuracy of the meter.

Currently available methods of monitoring meter accuracy involve an on site comparison with another meter. This is expensive in terms of the manpower required for a manual comparison and generally cannot be carried out very often or regularly. An object of the present invention is the provision of a device which overcomes the above mentioned problems by regularly and automatically monitoring the accuracy of electricity meters.

SUMMARY OF THE INVENTION The present invention provides a device for monitoring the accuracy of an electricity meter, said device including: a meter interface which monitors the reading on said meter and any changes therein; a status display; a communications port; a central processing unit which stores data relating to one or more preset load changes associated with each load; and a load sensor which indicates when one or more loads are switched on or off; wherein said processing unit compares the value of a load change indicated by a change in said reading with the preset load change associated with said load switching; and wherein said comparison can be stored as a record in non-volatile memory within said processing unit, displayed on said status display and communicated via said communications port to a remotely positioned monitor.

Preferably the or each load includes known and fixed loads for consumer appliances. Preferably said loads are selected from one of the following group: hot water cylinder; storage heater; and a combination of these. Dummy loads which are specifically designed for use with the device may also be used.

In its cheapest form the device uses the natural operating cycle of said appliances.

Greater accuracy can be achieved by further including a load control unit which is controlled by said device such that said appliances are switched on and off more frequently than the natural switching cycle. A specific test pattern may be implemented using a device which further includes a real-time clock.

Preferably said central processing unit derives the following statistical parameters relating to the meter accuracy from said comparison: mean; standard deviation; cross-correlation co-efficient; auto-correlation co-efficient.

The electricity utility may remotely or directly monitor the status of the meter using said communications port and any suitable communications link.

BRIEF DESCRIPTION OF THE DRAWING By way of example only, a preferred embodiment of the present invention is described in detail with reference to the accompanying drawing in which:

Fig. 1 shows a device 2 for monitoring the accuracy of an electricity meter 8 using the natural switching cycle of a hot water cylinder 9 in diagrammatic form.

DETAILED DESCRIPTION OF THE INVENTION

The device 2 includes an electricity consumption meter interface 3, a central processing unit 4, a meter status display 5, a communications port 6 and a load sensor 7.

The central processing unit 4 includes non-volatile memory which is pre-programmed with set-up parameters including the load (in Kw) associated with the hot water cylinder 9. The meter interface 3 signals the meter 8 reading to the central processing unit 4.

The particular type of interface 3 will depend on the meter 8 being tested. The most suitable is a pulsing interface 3 for a disk-type meter or a solid state meter.

The load sensor 7 may be any sensor capable of determining that power is being applied to a load of the quantum of that power; for example, a current transformer sensor. Each time the hot water cylinder 9 switches on or off, as signalled by the load sensor

7, the central processing unit 4 compares the change in the meter 8 reading (in Kw) with the pre-programmed hot water cylinder 9 load change (in Kw). The central processing unit 4 will then tabulate each comparison in the non-volatile memory, and from this (with appropriate programming) will derive statistical data relating to the accuracy of the meter 8 with respect to 7 0064 the known load change. This information enables an assessment of the overall accuracy of the meter 8 and also the detection of meter 8 tampering.

The data compiled by the device 2 can be displayed on the status display 5 and can be communicated externally via the communications port 6. Preferably the display 5 indicates the status of the power supply, the device 2 status (operational or not) and warning lights indicating for example an intolerable inaccuracy or a tampering of/with the meter 8.

The display 5 could display a graphic form indicating the historical accuracy of the meter 8, if so desired. The display 5 could be hand-held and remote, if so desired. Preferably the external communications link, if extant, is a dedicated link. The device 2 is not restricted to the utilisation of a single load, and can in fact use any number of known and fixed loads. The device 2 may use known and fixed consumer appliances as loads or it may utilise dedicated dummy loads.

While the invention has been described with reference to the natural cycle of a consumer appliance, the device 2 may include a load controller 10 which operates the load or loads independently of their natural cycle, if so desired. The meter 8 may then be tested at anytime and more frequently, thereby increasing the accuracy of the device 2.

While the invention has been described with reference to a central processing unit 4 within the device 2, it will be appreciated that such a processing unit 4 need not be a unit dedicated to the device 2 alone. For example, the unit 4 could form a part of a separate computing device (a personal computer) or other monitoring apparatus with a processing unit microprocessor or microcontroller. If so desired, the unit 4 could be the microcontroller disclosed in PCT/N296/00110 (to Southpower Ltd) as a part of the device for the operation of appliances, utilities and services within a building.

The set-up parameters of the device 2 include any or all of: the number of loads used, their identification, their wattage value, the threshold point for each type of meter 8, related warning (for example tampering and general inaccuracy - these are related to the statistical data derived by the central processing unit 4), the frequency and pattern of testing cycles (if used), the meter constant (watt/pulse) associated with the meter 8, and the pre-defined threshold point of accuracy of the meter 8. The device 2 may also include a real time clock (not shown); if so desired. The clock would be used in the testing cycles and to log certain events, such as tampering, in the memory of the central processing unit 4.

Claims

1. A device for monitoring the accuracy of an electricity meter, said device including: a meter interface which monitors the reading on said meter and any changes therein; a status display; a communications port; a central processing unit which stores data relating to one or more preset load changes associated with each load; and a load sensor which indicates when one or more loads are switched on or off; wherein said processing unit compares the value of a load change indicated by a change in said reading with the preset load change associated with said load switching; and wherein said comparison can be stored as a record in non-volatile memory within said processing unit, displayed on said status display and communicated via said communications port to a remotely positioned monitor.

2. A device for monitoring the accuracy of a meter as claimed in claim 1 wherein the or each load includes consumer appliances for which a preset load value is determined and stored within said microprocessor.

3. A device for monitoring the accuracy of a meter as claimed in either claim 1 or claim 2 wherein said loads are selected from one of the following group: a hot water cylinder; a storage heater; and a combination of these.

4. A device for monitoring the accuracy of a meter as claimed in any one of the preceding claims wherein said device further includes a load control unit capable of switching each said load on and off more frequently that the natural switching cycle of each load.

5. A device for monitoring the accuracy of a meter as claimed in any one of the preceding claims wherein said central processing unit derives the following statistical parameters relating to the meter accuracy from said comparison: mean; standard deviation; cross-correlation co-efficient; and auto-correlation co-efficient.

6. A device for monitoring the accuracy of a meter as claimed in any one of the preceding claims wherein the status of said device may be reviewed remotely by an electricity utility, said remote review being via information downloaded using the communications port and a suitable communications link.

7. A device for monitoring the accuracy of a meter as claimed in any one of the preceding claims wherein the data relating to the accuracy of the meter and to the values of each preset load include data in one or more of the following groups: the number of loads used; the identification of each load; the wattage value of each load; the threshold point for each type of meter 8; the frequency and pattern of testing cycles (if used); the meter constant (watt/pulse) associated with the meter; and the pre-defined threshold point of accuracy of the meter.