GB2280962A

GB2280962A - Commodity metering apparatus

Info

Publication number: GB2280962A
Application number: GB9320006A
Authority: GB
Inventors: Ronald Warwick
Original assignee: Siemens Measurements Ltd
Current assignee: Siemens Metering Ltd
Priority date: 1993-08-12
Filing date: 1993-09-28
Publication date: 1995-02-15
Anticipated expiration: 2013-09-28
Also published as: GB9320004D0; GB9316775D0; GB2280961B; GB9320006D0; GB2280961A; GB2280960A; GB2280962B; GB9320005D0; GB2280960B

Description

A COMMODITY METERING APPARATUS 2280962 The present invention relates to

commodity metering apparatus and more particularly to the metering of the supply of electricity from an electricity supply to a consumer.

There are many known methods of defrauding the supplier, the basis of most being either to effect the registration of power on the consumer meter or to obtain power from a point prior to the place where the consumed energy is registered.

Prior art forms of fraud detection are capable of detecting the use of a black box across the metering terminals of the consumer meter which results in a measured energy discrepancy between the supplied energy and the measured energy. The use of a current shunt in the form of the application of a wire link across the metering terminals to shunt some of the supplied energy without being metered will also result in a discrepancy between the supplied energy and the measured energy. The cutting of the neutral terminal to the consumer meter will switch the meter off and it will no longer measure the consumed power. The meter will record the times at which power has been removed and these may be compared with known power interruptions in the grid and used to detect fraudulent removal of power.

The present invention is arranged to detect the above methods of fraud and also allows monitoring of the anti-fraud system integrity.

An object of the present invention is to provide commodity metering apparatus in which the integrity of an anti-fraud device is monitored and capable of detecting more methods of frauds than known systems.

According to the present invention there is provided commodity metering apparatus comprising a consumer meter arranged to be connected to an electricity supply, in which a live cable is connected to the meter via a fuse, a first current sensor arranged to monitor the current at an input to the fuse and a second current sensor arranged to monitor the current at an output of the fuse, said first and second sensors being connected to a comparator circuit by a respective two-wire pair, and arranged to detect any imbalance there between, characterised in that the first current sensor is provided with a second output which is connected to a tone verification circuit by way of a further two-wire pair, and said meter includes means for generating a tone which is circulated around the two, two-wire pairs and monitored by said tone verification circuit.

Preferably the means for generating the tone comprises an oscillator and amplifier, and the tone verification circuit includes a band pass filter for monitoring the received tone signal.

Preferably each two-wire pair is protected by a neutral or earth shield.

An embodiment of the present invention will now be described with reference to the accompanying drawing which shows a block diagram of commodity metering apparatus in accordance with the present invention.

Referring to the drawing, there is shown a commodity meter 2 which receives a Main input over a live cable 4 and a neutral cable 6. The neutral cable 6 passes directly through the meter to the load 8. The live cable is connected to the input of a fuse 10, the output of which is fed through the meter to the load 8. A primary current sensor 12 surrounds the input cable to the fuse 10 and includes a first winding, the outputs of which are connected by a two-wire pair 14 to an input of a current balance comparator and current sensor tone verification circuit 16. The output of the fuse 10 is surrounded by a secondary current sensor 18 having a winding which is connected to the circuit 16 by way of a two- wire pair 20. The use of a primary current sensor and a secondary current sensor is well known in the art, and to compare the output of the respective coils in a comparator circuit is also well known. However, the present invention uses a second winding on the primary current sensor, the outputs from which are connected to the circuit 16 over a further two- wire pair 22. This further two-wire pair 22 carries a tone signal which is generated by conventional means from, for example, an oscillator and amplifier contained within the meter 2 and may conveniently form part of circuit 16 so that the meter 2 always expects to receive the tone signal back via the two-wire pair 14. In the event that the primary current sensor is interfered with, the integrity of the path 22 and 14 will be lost and the meter will register the fact that a possible fraud has been perpetrated.

As a further precaution, the connections 14 and 22 may be protected an earth or neutral shield so that if an attempt is made to short circuit the output of the fuse 10 with the sense line, damage will occur.

It will also be appreciated that a band pass ffiter may be used in the circuit 16 in order to detect the tone signal.

The detection system may activate an indicator or preferably the invention is used in conjunction with a two way communication system between the meter and the commodity supplier. Such a system may be via a radio system mains signalling or be telephone based. Alternatively a two way electronic token, eg. electronic key or smart card, may be used in the meter which may be removed and downloaded for analysis by the energy supplier.

The present invention detects the methods of fraud mentioned above, and also detects cutting of the communication link. Furthermore, the insertion of a dummy fuse with power tapped off at Main will cause an imbalance to be detected between the current sensors, and the imbalance will be Ragged as a fraud.

1

Claims

1. Commodity metering apparatus comprising a consumer meter arranged to be connected to an electricity supply, in which a live cable is connected to the meter via a fuse, a first current sensor arranged to monitor the current at an input to the fuse and a second current sensor arranged to monitor the current at an output of the fuse, said first and second sensors being connected to a comparator circuit by a respective two-wire pair, and arranged to detect any imbalance there between, characterised in that the first current sensor is provided with a second output which is connected to a tone verification circuit by way of a further two-wire pair, and said meter includes means for generating a tone which is circulated around the two, two-wire pairs and monitored by said tone verification circuit.

2. Commodity metering apparatus as claimed in Claim 1, wherein the means for generating the tone comprises an oscillator and amplifier, and the tone verification circuit includes a band pass filter for monitoring the received tone signal.

3. Commodity metering apparatus as claimed in Claims 1 or 2. wherein each two-wire pair which carries the tone signal is protected by a neutral or earth shield.

4. Commodity metering apparatus substantially as hereinbefore described widi reference to the accompanying drawing.