GB2281401A

GB2281401A - Electricity consumption meter

Info

Publication number: GB2281401A
Application number: GB9409853A
Authority: GB
Inventors: Kenneth Payne
Original assignee: Ampy Automotion Digilog Ltd
Current assignee: Landis and Gyr Ltd
Priority date: 1993-08-28
Filing date: 1994-05-17
Publication date: 1995-03-01
Anticipated expiration: 2014-05-17
Also published as: GB9409853D0; GB2281401B

Abstract

An electricity meter (11) for measuring the electrical energy supplied to a load, the meter having a switch (3) for interrupting the supply to the load comprises: means 7 for generating a signal 14 to indicate whether the switch is open; and logic means 9 to generate a warning signal (e.g. by transmission of the meter I.D. to the supply company) if the voltage drop across supply terminals 4 and 5 is below a threshold value while the switch is open, thereby indicating fraudulent use of the meter. <IMAGE>

Description

Title: Electricity Consumption Meter Field of invention This invention concerns electricity metering apparatus, and in particular the detection of fraudulent connections to such meters to enable consumption of electricity by a consumer without correct payment therefor. In the context of this application a "consumer" comprises any load which when connected to a source of electricity will draw current therefrom. Typically a consumer in this context is the electrical load represented by a private dwelling.

Background to the invention Electricity consumption meters normally measure the current flowing from the supply to the consumer in the live (phase) wire of the supply. In the case where the meter is a prepayment meter, a common method of defrauding such a metering arrangement is to connect an external short circuit or shunt, such as a piece of wire, between the live of the supply and the live terminal of the consumer side of the meter. This places a current path in parallel with the current sensor within the meter. The eFfect is to divert a proportion of the load current away from the current measuring sensor so that some of the current supplied to the consumer bypasses the meter. The total amount of energy consumed is therefore not measured by the meter and enables the consumer to obtain electricity that is otherwise not paid for.

If the meter is a prepayment meter which includes an internal contactor switch to isolate the consumer when the credit is exhausted, the external shunt nullifies the effect of opening the contactor with the result that the consumer continues to receive electrical power, and no record of the supply is made and no payment therefor is made.

This method of fraud can be applied equally to electromechanical meters as well as solid state based electricity meters.

It is an object of the present invention to provide a device for detecting such a fraudulent connection.

Summary of the invention According to the present invention in an electricity meter for measuring the quantity of electrical energy supplied from an electrical power supplier via an electrical power distribution network comprising live and neutral supply cables to a consumer, wherein the meter is connected in series with the consumer so that the current flowing to the consumer normally passes through the meter and the meter includes, or has associated therewith, switch means for interrupting the supply of current, there is provided: a) voltage measuring means for measuring the potential difference between the supply side of the meter and Ene consumer side of the meter and generating a first output signal if any potential difference greater than a given threshold is detected and a second output signal if a potential difference less than the threshold is detected; b) signal generating means indicative of whether the switch means is open circuit; and c) logic circuit means responsive to the output of the voltage measuring means to generate a warning signal in the event that a potential difference less than the given threshold exists between the input and ouput sides of the meter whilst the switch means is in its open condition.

The meter may be a prepayment meter, in which case the prepayment means in the meter may produce a signal to the logic circuit means when the switch means is open or the prepaid credit is exhausted.

The signal from the prepayment means may be derived from a control circuit adapted to operate the switch means.

Alternatively the signal from the prepayment means may be derived directly from contacts on the switch means.

Alternatively the signal from the prepayment means may be derived from the prepayment means such that the logic circuit means will generate a warning signal if there is no prepayment credit remaining.

Since the internal shunt between the meter possesses electrical resistance to enable the current flowing through the meter to be legitimately monitored, a very small potential difference will exist between the supply and consumer side of the meter when the latter is operating normally with the switch means closed. This situation will be ignored by the logic circuit means since the signal from the switch means (or the prepayment means) will indicate that the meter is operating normally. If the voltage measuring device of the invention were set to only detect a complete short circuit (ie virtually zero resistance) then the fraudulent connection of a low resistance across the meter would result in a small voltage drop and in this event the fraudulent condition would not be detected. It is thus important that the voltage sensing circuit is capable of responding if there is a short circuit or a small voltage developed across the meter but is adjusted so as not to respond in the event that the voltage across the meter is substantially equal to the supply voltage.

The warning signal may be stored secretly within the meter or may produce a temporal or permanent change in a display device associated with the meter, or may generate a signal which can be transmitted either by radio or FM modulation or the like along the supply lines to the electrical supply company. Any such generated signal may include an identification indicating the number of the meter of some other unique identification so that the location of the meter can be determined from records, and the electrical supply company can be alerted as to where a fraudulent connection is occurring.

Information stored or transmitted may also relate to the time and date as well as identification of the meter by number or geographical location or consumer number or the like.

The invention also lies in a method of detecting fraudulent use of an electricity meter by the connection of a conductive element between the supply and consumer side of the meter comprising tne steps of: a) monitoring the potential difference between the consumer and supply side of the meter; and b) generating a warning signal if a potential difference substantially less than the supply voltage is detected at a time when an electrical switch means associated with the meter has been operated so as to inhibit the flow of electrical current through the meter.

In the case of a prepayment meter, the warning signal may be generated when any prepayment for electricity has become exhausted.

The method also envisages the use of the warning signal to sound an alarm, illuminate a light, cause a permanent or temporary change in the device such as a fusible link which may or may not be visible from outside the meter, secretly storing a signal indicating that fraudulent use has occurred, optionally with data relating to the time and date and/or identity of the meter and/or consumer.

The method may also comprise the step of transmitting data, relating to the detection of a fraudulent connection as aforesaid, by any known means. This may, for example, be by radio transmission, by radio telephone link or by transmission of signals along the supply lines to the electrical supply company to alert the latter that a fraudulent connection has been made.

Brief description of the drawings The invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a simplified schematic diagram of a conventional solid state electricity measuring meter in the prior art, Figure 2 shows the meter of Figure 1 being used in a fraudulent manner, and Figure 3 shows the meter modified to detect the fraud, in accordance with the invention.

Description of embodiment The prepayment meter 11 of Figure 1 is shown in normal use. The current sensor 1 is connected in series with a switch contactor 3 between a supply terminal 4 and a load terminal 5 of the meter 11. In common with conventional practice, the meter supply side is connected to the live of the electrical supply cable and the live terminal of the load is connected to the other side of the meter so that the meter is set to measure the current flowing from the live side of the supply to the load.

A signal on line 2 represents the voltage at terminal 4.

A signal 12 developed by the current sensor 1 is representative of the current flowing between the terminals 4 and 5. The two signals 2 and 12 are supplied to a circuit means 6 which computes the quantity of energy being consumed.

The opening and closing of contactor 3 is performed by a control circuit 7 which may for example be token operated or card operated or a coin freed mechanism or any other device for organising the supply of current following appropriate prepayment, and capable of communicating with and controlling the contactor 3.

Figure 2 shows the meter 11 with a conductive element 8 connected fraudulently, externally of the meter, between terminals 4 and 5. This connection provides a parallel current path to the load current, diverting a proportion of the current away from the current sensor 1 so that a reduced quantity of current is measured by the sensor 1 and the quantity of energy registered in 6 is less than should be the case.

Figure 3 shows the addition of voltage measuring circuit means 9 in accordance with the invention. The voltage on line 2 and the voltage on line 10 (corresponding to the voltage at the live terminal of the consumer), are supplied to the two inputs of circuit 9 which determines any potential difference therebetween.

Under normal (non-fraudulent) use of the meter, Figure 1, and with the contactor 3 closed, current flows to the consumer and there is little or no potential difference between terminals 4 and 5. If the contactor is open thereby preventing the flow of current to the consumer (for any reason but primarily because the payment has expired) then the potential difference between the terminals 4 and 5 will be substantially that of the supply. This will be detected by circuit 9.

During fraudulent use of the meter such as is shown in Figure 2, the potential at terminal 4 will be substantially the same as the potential at terminal 5 in view of the short circuit produced by item 8. The circuit 9 is arranged to determine when this condition exists and to generate a warning signal at 13 when 4 and 5 are at substantially the same potential and contacter 3 is open.

By the same token the circuit 9 can be arranged to generate another signal when the voltages at terminals 4 and 5 are substantially the same and the contactor is closed (ie non-fraudulent operation of the meter).

To this end a signal is supplied along 14 from the contactor control 7 to the circuit 9 to indicate the state of the contactor 3.

The signal along line 14 may alternatively be derived from the prepayment circuit so as to indicate when prepayment has expired and to generate a fraud signal at 13 if the voltages at 4 and 5 are found to be the same.

The fraud signal at 13 may be used in a number of ways to indicate that a fraud has been or is being committed. For example, a light may be illuminated on the front of the meter, or data may be stored secretly within the meter indicating that a fraud has occurred; and in a more sophisticated arrangement both time and date and extent of the fraud may be recorded in this way. Alternatively, information indicating that a fraud is being committed, and indicating in some unique way the particular meter concerned, may be transmitted either by radio or radio telephone or by propagation along the supply cables to the supplier.

The invention may be applied to any single phase twin element or polyphase electricity meter capable of interrupting the flow of current from a supplier to a consumer.

The functions of items 6, 7 and 9 may be performed by a microprocessor-based circuit and associated circuitry.

Power for operating the microprocessor based circuitry and/or any other fraud detector circuitry may be derived from the electricity supply upstream of the meter and internally connected to the supply side terminal of the meter so that the meter has to be broken into if the circuits concerned are to be disabled.

Claims

1. An electricity meter for measuring the quantity of electrical energy supplied to a consumer by an electrical power supplier via electical power distribution lines including live and neutral supply cables, wherein the meter is connected in series with the consumer so that the current flowing thereto normally passes through the meter, and wherein the meter includes, or has associated therewith, switch means for interrupting the supply of current, comprising: a) voltage measuring means for measuring the potential difference between the supply side of the meter and the consumer side of the meter and for generating a first output signal if any potential difference greater than a given threshold is detected and a second output signal if a potential difference less than the threshold is detecLed; b) signal generating means indicative of whether the switch means is in an open circuit condition; and c) logic circuit means responsive to the output of the voltage measuring means to generate a warning signal in the event that a potential difference less than the given threshold exists between the it and output sides of the meter whilst the switch means is in the open circuit condition.

2. A meter according to claim 1 further comprising prepayment means in the meter for producing a signal to the logic circuit means when the switch means is in the open condition or the prepaid credit is exhausted.

3. A meter according to claim 2 in which the signal from the prepayment means is derived from a control circuit adapted to operate the switch means.

4. A meter according to claim 2 in which the signal from the prepayment means is derived directly from contacts on the switch means.

5. A meter according to claim 2 in which the signal from the prepayment means is derived from the prepayment means such that the logic circuit means will generate a warning signal if there is no prepayment credit renaining.

6. A meter according to any one of claims 1 to 5 in which the warning signal is stored secretly within the meter, or produces a temporal or permanent change in a display device associated with the meter, or generates a fault signal which can be transmitted back either by radio or FM modulation or the like along the distribution lines to the electrical power supplier.

7. A meter according to claim 6 in which said fault signal includes an identification indicating the number of the meter, or some other unique identification, so that the location of the meter can be determined from records, and the electrical supplier can be alerted as to where a fraudulent connection is occurring.

8. A meter according to claim 6 of claim 7 in which the signal stored or transmitted also relates to the time and date of occurence of the warning signal, as well as identifying the meter by number or geographical location or consumer number or the like.

9. A method of detecting fraudulent use of an electricity meter by the connection of a conductive element between the supply and consumer side of the meter, comprising the steps of: a) monitoring the potential difference between the consumer and supply side of the meter; and b) generating a warning signal if a potential difference substantially less than the supply voltage is detected at a time when an electrical switch means associated with the meter has been operated so as to inhibit the flow of electrical current through the meter.

10. A method according to claim 9 in which the meter is a prepayment meter: and the warning signal is generated when any prepayment for electricity has become exhausted.

11. A method according to claim 9 or claim 10 in which the warning signal sounds an alarm, illuminates a light, causes a permanent or temporary change in a device such as a fusible link (which is visible or not from outside the meter), secretly stores a signal indicating that fraudulent use has occurred, optionally with data relating to the time and date and/or identity of the meter and/or consumer.

12. A method according to any one of claims 9 to 11 and further comprising the step of transmitting data relating to the detection of a fraudulent connection as aforesaid, by any known means.

13. A method according to claim 12 in which the data is transmitted by radio transmission, by radio telephone link or by transmission of signals along the supply lines to the electrical power supplier to alert the latter that a fraudulent connection has been made.

14. An electricity meter substantially as herein described with reference to, and as shown in, the accompanying drawings.

15. A method of detecting fraudulent use of an electricity mether substantially as herein described with reference to, and as shown in, the accompanying drawings.