GB2334338A

GB2334338A - Tamper detection in electro-mechanical electricity consumption meters

Info

Publication number: GB2334338A
Application number: GB9803036A
Authority: GB
Inventors: Nicholas Andrew Thoma Mitchell; Adrian Thomas Shingler
Original assignee: ABB Metering Systems Ltd
Current assignee: ABB Metering Systems Ltd
Priority date: 1998-02-12
Filing date: 1998-02-12
Publication date: 1999-08-18
Also published as: GB9803036D0

Abstract

An apparatus 11 is described, for detecting tamper in an electro-mechanical electricity consumption meter 1 of a type having a sealed housing 2, 3; at least one rotatable component (21 Fig 2 not shown) whose rate of rotation is related to the rate of consumption of electricity; connecting terminals 6, 7 for connecting the meter to an electricity supply and to a load and at least one removable sealable terminal cover 8 for preventing access to at least one of said terminals 6, 7 (is described). The apparatus comprises a module 11 which can be fitted outside the sealed housing of the meter and enclosed by the sealable terminal cover. The module 11 includes electrical circuit means (13) which is operable to detect tamper to the meter. Preferably the module 11 includes an optical pick-up (17) for detecting rotation of the rotatable component (21) through the sealed housing and the electrical circuit means (13) is operable to detect for reverse rotation of the rotatable component indicating the meter is being tampered with. In a preferred arrangement a magnetic field sensor (15) for measuring the magnetic field strength in the vicinity of the connecting terminals is included to detect for the presence of stray magnetic fields and to give a measure of the current passing through the meter. With such an arrangement the electrical circuit (13) includes means for comparing the outputs from the magnetic field sensor (15) and the optical pick-up (17) to determine if there is a mismatch indicating the meter is being tampered with.

Description

Tamper Detection in Electro-Mechanical Electricity Consumption Meters This invention relates to electro-mechanical electricity consumption meters and is especially concerned with an apparatus for detecting when such a meter has been, or is being, tampered with.

Electro-mechanical electricity consumption meters are well known and have been used for many years. Typically such meters log the total number of units of electricity consumed since the installation of the meter and store this information mechanically using numbered barrel registers or dial registers which are visible through a window in the meter housing. Often termed "Ferraris meters", these meters measure electricity consumption using voltage and current electromagnets which are arranged to induce eddy currents into a disc, commonly referred to as a "Ferraris disc", such that the rate of rotation of the disc is proportional to the rate of consumption of electricity. The disc is part of a rotor assembly which is coupled by a drive arrangement to the mechanical registers. As the disc rotates, the mechanical registers record the number of rotations and thus the amount of electricity consumed.

It is estimated that there are currently in excess of 20 million Ferraris-type electromechanical meters in domestic operation in the UK. It has also been estimated that in certain geographic areas in the UK up to 20% of the electricity supply is lost as a result of meter fraud. In the case of electromechanical electricity meters it is well known that attempts to defraud such meters are not easy to detect.

For example it is known to slow, or even stop, the rotation of the rotor assembly by mechanically interfering with it. The rotor assembly is usually rotatably supported using a magnetic suspension arrangement such that it can rotate virtually frictionlessly. As a result even the smallest mechanical interference, for example a wire or hair applied to the edge of the disc, can significantly slow rotation of the disc and so reduce the total number of units of electricity recorded. To prevent this form of tamper the meter is enclosed in a sealed housing and any damage to the housing is taken as an indication that the meter has been tampered with. Although such damage may indicate that tampering has probably taken place it is unlikely that this will be sufficient evidence for the electricity supplier to take action against the offender. Furthermore it is impossible to quantify how much electricity will have been lost prior to detecting this form of fraud.

Since the rotor assembly is driven by electro-magnetic induction and rotatably supported by means of a magnetic field this makes it possible to slow, stop or even reverse the rotation of the disc using permanent magnets or electromagnets located outside the meter's sealed housing. Although the meter's housing is designed to prevent normal strength magnets being placed in close enough proximity to the rotor assembly to have any effect, the cost of strong permanent magnets is falling, making this form of tamper more practicable.

It is also known to slow, or even stop, rotation of the disc by tilting the meter away from a vertical orientation. To prevent this form of tamper the meter is arranged such that the fixing screws used to secure the meter during installation are only accessible by removal of the sealed terminal cover. Although such a fixing arrangement substantially eliminates this form of tamper it is not unknown for the meter to be installed on a board which is attached to the wall of the consumer's property. When the meter is installed in this manner this makes it possible to tilt the meter by tilting the board.

A further form of meter fraud consists of connecting an electrical bypass in order to obtain electricity without the meter logging its use. If it is suspected that bypassing of the meter is taking place, a site visit must be made to prove that the meter is being bypassed so that action can be taken against the offender. Past experience all too often shows that before a meter inspection can be made the offender has removed the bypass such that the meter has resumed normal operation. This makes the detection, but equally importantly the proof, of meter bypassing difficult in practice.

In contrast to electro-mechanical meters, electronic electricity consumption meters which often include a micro-processor are able to detect and log many possible forms of tampering. One example is for such meters to measure and store the number of units of electricity apparently consumed for reverse operation. Another example is to record the date and time whenever the electricity supply is interrupted. The electricity supplier can then compare this record with the number of power failures known to have occurred and any discrepancy in these two readings will indicate that a site visit may be necessary to check for tampering or for a genuine fault.

Although electronic meters are better able to detect many forms of tamper they have a major drawback in that their operating life is typically of the order of ten years. In contrast, electro-mechanical electricity consumption meters are extremely reliable in their operation and have been used in continuous service for 50 years, requiring only minimal refurbishment every 25 years or so. To include electronic circuitry in such a meter would reduce the operating life of the meter and would make it prohibitively expensive as it would include additional circuitry which is redundant in the vast majority of applications since tampering is restricted to a very small number of consumers.

A need exists, therefore, for a way of detecting tamper to an electro-mechanical electricity consumption meter which is reliable, inexpensive and which will not compromise the operating life of the meter. It is an object of the present invention to provide an apparatus which, in part at least, overcomes this problem.

According to the present invention there is provided an apparatus for use with an electro-mechanical electricity consumption meter of a type having a sealed housing; at least one rotatable component whose rate of rotation is related to the rate of consumption of electricity; connecting terminals for connecting the meter to an electricity supply and to a load and at least one removable sealable terminal cover for preventing access to at least one of said terminals; the apparatus comprising: an electrical circuit means connectable to said meter and operable for detecting tamper to the meter, said circuit being adapted to be located outside the sealed housing of the meter and enclosed by the sealable terminal cover. Since the apparatus is located externally ofthe meter's sealed housing it can be fitted once the meter has been installed or fitted to existing meters if required. Furthermore the operating life expectancy of the meter is not compromised in any way since no electricaVelectronic components are housed inside the meter.

Advantageously the apparatus further comprises an optical pick-up for detecting rotation of the rotatable component through the sealed housing of the meter. Preferably the optical pick-up comprises a light source arranged to direct light through the sealed housing onto the rotating component and at least one light detector which is arranged to detect light reflected from the component back through the sealed housing. With such an arrangement it is preferred that the electrical circuit means is operable to detect for reverse rotation of the rotatable component indicating the meter is being tampered with.

In a preferred embodiment the apparatus further comprises a sensor for measuring the magnetic field strength in the vicinity of the meter's connecting terminals to detect for magnetic fields. Preferably the sensor and electrical circuit means are operable to detect the presence of static or alternating magnetic fields. Alternatively or in addition the sensor is located in close proximity to the load connecting terminals of the meter and is operable to produce an electrical signal related to the amount of current passing through the load terminals in dependence on the magnetic field in the vicinity of said terminals. The sensor advantageously comprises a pick-up coil or a Hall effect sensor.

In a preferred arrangement when the apparatus includes an optical pick-up the electrical circuit includes means for comparing the outputs from the magnetic field sensor and the optical pick-up to determine if there is a mismatch indicating the meter is being tampered with.

Preferably the apparatus further comprises means for detecting movement of the apparatus away from a desired orientation indicating the orientation of the meter has been tampered with. Advantageously the means for detecting for movement of the circuit comprises a mercury tilt switch. Preferably the apparatus further comprises switching means arranged such as to be actuated by removal of the terminal cover.

According to a further aspect of the invention an electro-mechanical electricity consumption meter is adapted to receive apparatus as described above. Preferably in such a meter the sealable terminal cover is adapted such as to enclose the apparatus and the sealed housing of the meter is adapted to include a window such that the rotatable component is visible through the sealed housing from under the sealable terminal cover.

An apparatus in accordance with the invention will now be described by way of example only with reference to the accompanying drawings in which: Figures la and lb are schematic perspective views of an electro-mechanical electricity consumption meter (a) as an exploded view with the terminal cover removed showing an apparatus in accordance with the invention; and (b) with the apparatus and terminal cover fitted to the meter; Figure 2 is a schematic sectional view of the meter of Figure 1 through the terminals showing apparatus in accordance with the invention; and Figure 3 is a schematic of the optical pick-up assembly of the apparatus.

Referring to Figures la and ib there is shown an electro-mechanical electricity consumption meter 1 of a type known in the art. The meter 1 includes a sealed housing which comprises a base 2 and casing 3 which are held together using a sealable fixture (not shown). The sealable fixture is applied by the meter manufacturer to certify the accuracy of the meter 1 and to prevent access to the interior of the meter.

Electricity is supplied to, and withdrawn from, the meter 1 by a respective pair of power inlet cables 4 and power outlet cables 5 which are connected to respective electrical connecting terminals 6 and 7.

The meter 1, which is of a known type, operates in a conventional manner and accordingly the internal mechanism will not be described in detail. It is sufficient to state that the meter includes voltage and current electromagnets, a rotor assembly and barrel or dial registers for displaying the consumption information through a window 10 in the front face of the meter. As is known, the rate of rotation of any of these rotatable components is related to the rate of consumption of electricity.

Once the meter 1 has been installed and the electricity inlet cables 4 and outlet cables 5 connected, a terminal cover 8 is fitted over the electrical terminals to prevent access to them and secured using a screw 9. As is known the screw 9 is sealable to prevent unauthorised removal of the terminal cover and thereby prevent access to the connecting terminals 6 and 7.

Also shown in Figure la is an electronic module 11 in accordance with the present invention which can detect when the meter has been tampered with. The module 11, which is described in detail below, is fitted to the meter l either during installation of the meter or at a later date when required. To fit the module 11 the terminal cover 8 is removed and the module 11 attached to the meter. Electrical power to drive its electrical circuitry is derived from the output connecting terminals 7 using connectors 25 which extend from the module 11 and engage in the connecting terminals. As is shown in Figure ib, the terminal cover 8 is then replaced and sealed thereby enclosing the module 11 and preventing access thereto.

In a preferred arrangement the module 11 is mechanically held to the terminal cover 8 using clips, enabling the module 11 and terminal cover 8 to be fitted as a single unit in one operation by an unskilled operator. With such an arrangement the electrical connections 25 are arranged to engage with the connecting terminals 7 when installing the combined unit.

Referring to Figure 2, there is shown a schematic cross-section through the meter of Figure 1 in the region of the electrical connecting terminals 7. The electronic module 11 comprises a power supply unit (PSU) 12, electronic circuitry 13, a mercury tilt switch 14, a Hall effect sensor 15, a micro-switch 16 and an optical pick-up assembly 17. The power supply unit 12 which derives its electrical power from the output connecting terminals 7 converts the mains voltage, which is typically 240 volts RMS, to a low voltage DC supply which is used to power the electronic circuitry 13.

The electronic circuitry 13 in the embodiment described comprises a microprocessor based circuit which includes nonwolatile memory and a real time clock/calendar. It will be appreciated by those skilled in the art that the circuit 13 can be implemented readily in a number of ways and for this reason the function of the circuitry 13 will be described.

The mercury tilt switch 14 is arranged such that it will be actuated should any attempt be made to tilt the meter away from its normal vertical orientation. The electronic circuitry 13, when detecting the operation of the switch 14, logs that a tamper event has occurred together with the time and date of the event. This information is stored in nonvolatile memory in the electronic circuit 13.

The micro-switch 16 is fitted under the terminal cover 8 such that when the terminal cover is removed the contacts of the switch open. Again, the electronic circuit 13, on detecting the opening of the switch, registers the time and date on which the tamper event occurred.

As described above the module 11 is preferably attached to the terminal cover 8 and the two fitted to the meter as a single unit. It will be appreciated that with such arrangement, the micro-switch 16 is arranged to operate by the relative movement of the module/terminal cover with respect to the meter housing 3. Preferably the switch is located in the lower portion of the module and is operable against a part 24 (Figure 2) of the surface of the sealed housing 3, in the vicinity of the connecting terminals. To ensure that any interference with the terminal cover is detected and recorded whilst the module 11 still has electrical power, the connectors 25 are of sufficient length to ensure they still remain in electrical contact with the connecting terminals when the micro switch 16 is actuated.

The Hall effect sensor 15 is located such that it is in close proximity to the output terminal 7. This sensor has two functions; firstly, it gives an indication of the current flowing though the meter; and secondly, it is used to detect the presence of external magnetic fields. Its function is described in detail below.

Referring to Figure 3, the optical pick-up assembly 17 comprises an infrared light emitting diode (LED) 18 and two photo transistors 19. The LED 18 is arranged to direct light 20 through the casing 3 and onto the under-surface of the rotor assembly disc 21.

The casing 3 is made from a transparent plastics material and hence the rotor assembly is visible through it.

Light 22 which is reflected from the surface of the disc is detected through the casing 3 by the photo transistors 19. The intensity ofthe reflected light 22 is modulated as the disc rotates by markings 23 on the surface of the disc. The optical pick-up 17 is thus capable of producing a signal which is related to the rate of rotation of the rotor assembly by utilising the relative movement of the markings 23 past the assembly 17.

Depending on the direction of rotation of the disc 21, this will affect the relative phase ofthe signals produced by photo transistors 19. The phase between these signals is used to determine the direction of rotation of the disc 21.

Under normal operation of the meter, the disc rotates in a clockwise direction (as indicated in Figure 3) at different rates of rotation depending on the rate of electricity consumption. Any form of tamper to the meter which results in the disc rotating in the opposite direction is detected by the optical pick-up 17. If the disc continues to rotate by an amount which exceeds a preset energy threshold, for example 10 watt hours - that is, 2 revolutions - the electronic circuitry 13 registers that reverse rotation has taken place and record the time and date of the event.

Since the optical pick-up 17 is also able to determine the number of revolutions of the disc as well as the direction of rotation, this enables the appropriate number of units of electricity lost due to reverse direction to be determined and stored in the memory. In practice, however, many electro-mechanical meters include an anti-reversing mechanism to prevent the mechanical registers being reverse wound. Such a mechanism prevents the rotor assembly from rotating in a specified direction for more than a preset number of revolutions, typically 2 or 3 revolutions. With such a meter it will be appreciated that it is not possible to accurately estimate the number of units of electricity lost due to fraud. It is however still worth attempting to log the total number of electricity units used during reverse operation with such a meter as the anti-reversing mechanism is prone to failure.

As stated above, the Hall effect sensor 15 provides two functions. In the first, the sensor gives a signal indicative of the current flowing through the meter by sensing the magnetic field strength in the vicinity of the connecting terminals 7. The electronic circuitry 13 compares this signal with the signal generated by the optical assembly 17.

The signal produced by the optical assembly 17 is related to the rate of rotation of the disc 21, which is proportional to the rate of consumption of electrical power. Since the power factor for the meter will be unknown, the signal from the optical pick-up assembly 17 can only give an indication of the actual electrical current passing through the meter. Notwithstanding this, a gross-mismatch between the current measured by the Hall effect sensor 15 and that of the optical assembly gives an indication that tampering is taking place. When the electronic circuitry 13 detects a difference between these signals which exceeds a preset threshold, a tamper/fraud flag is set and stored in the nonvolatile memory. This condition will occur if a load current is being drawn from the meter, which will be detected by the current sensor, but the disc is not rotating correctly.

Such a condition can be caused by a failure of the voltage electromagnet coil or an attempt to tamper with the meter's operation by tilting the meter away from a vertical orientation or slowing, or even stopping, rotation ofthe rotor assembly using mechanical interference.

A second function of the Hall effect sensor 15 is to detect the presence of magnetic fields which may be generated externally of the meter's sealed housing and applied in an attempt to interfere with the meter's performance. These fields may be either AC, as would be generated from cables looped around the meter, or DC, as would be generated from permanent magnets. If an external DC field is detected then the electronic circuitry 13 sets a tamper/fraud flag. In the case of an external AC field, the electronic circuit compares the signal from the Hall effect sensor and that from the optical assembly to determine if there is a constant difference between their readings which exceeds a preset threshold. The presence of a constant difference is an indication that an AC field is being externally applied to the meter to slow the operation of the meter.

It will be appreciated by those skilled in the art that modifications to the apparatus described can be made which are within the scope of the invention. Thus, whilst in the embodiment described the optical assembly is arranged to detect rotation of the disc 21 of the rotor assembly, it is also envisaged that other rotatable components within the meter could be used. For example, it is also envisaged to use a part of the magnetic suspension arrangement used to support the rotor assembly, provided it has suitable markings on its surface. In other embodiments, other rotating components could be utilised such as, for example, the barrel registers or dial registers. Furthermore, in the embodiment described, the disc is visible through the wall of the sealed housing as the meter casing 3 is made from a transparent plastics material. In other arrangements the meter can be specifically provided with a window in the sealed housing for this purpose or the optical assembly 17 can be mounted on the front window of the meter.

In the embodiment described the apparatus comprises a number of sensors for detecting a number of forms of tamper. It is also envisaged that apparatus is provided which includes one or all of the sensors described. A particular advantage of the present invention is that it can be fitted to an existing meter, after installation, should it be required. A further advantage of the present invention is locating the apparatus under the sealed terminal cover. Although in some meters this will require the cover to be adapted to enable the apparatus to be mounted, this enables the apparatus to be fitted without the need to include any form of electrical or electronic components inside the meter which might otherwise reduce the operating life of the meter.

Claims

CLAIMS 1. An apparatus for use with an electro-mechanical electricity consumption meter of a type having a sealed housing; at least one rotatable component whose rate of rotation is related to the rate of consumption of electricity; connecting terminals for connecting the meter to an electricity supply and to a load and at least one removable sealable terminal cover for preventing access to at least one of said terminals; the apparatus comprising: an electrical circuit means connectable to said meter and operable for detecting tamper to the meter, said circuit being adapted to be located outside the sealed housing of the meter and enclosed by the sealable terminal cover.
2. Apparatus according to Claim 1 and further comprising an optical pick-up for detecting rotation of the rotatable component through the sealed housing.
3. Apparatus according to Claim 2 wherein the optical pick-up comprises a light source arranged to direct light through the sealed housing onto the rotatable component and at least one light detector which is arranged to detect light reflected from the component back through the sealed housing.
4. Apparatus according to Claim 2 or Claim 3 wherein the electrical circuit means is operable to detect for reverse rotation of the rotatable component indicating the meter is being tampered with.
5. Apparatus according to any preceding claim and further comprising a sensor for measuring the magnetic field strength in the vicinity of the connecting terminals.
6. Apparatus according to Claim 5 wherein the sensor and electrical circuit means are operable to detect the presence of static or alternating magnetic fields.
7. Apparatus according to Claim 5 or Claim 6 wherein the sensor is located in close proximity to the load connecting terminals and is operable to produce an electrical signal related to the amount of current passing through the load terminals in dependence on the electro-magnetic field generated by said terminals.
8. Apparatus according to Claim 5, 6 or Claim 7 wherein the sensor comprises a pick-up coil.
9. Apparatus according to Claim 5, 6 or Claim 7 wherein the sensor comprises a Hall effect sensor.
10. Apparatus according to any one of Claims 3 to 9 when dependent on Claim 2 wherein the electrical circuit includes means for comparing the outputs from the sensor and the optical pick-up to determine if there is a mismatch indicating the meter is being tampered with.
11. Apparatus according to any preceding claim and further comprising means for detecting movement of the circuit away from a desired orientation indicating the meter has been tampered with.
12. Apparatus according to Claim 11 wherein the means for detecting for movement of the circuit comprises a mercury tilt switch.
13. Apparatus according to any preceding claim and further comprising switching means arranged such as to be actuated by removal of the terminal cover.
14. An electro-mechanical electricity consumption meter adapted to receive apparatus according to any preceding claim.
15. An electromechanical electricity consumption meter according to Claim 14 wherein the sealable terminal cover is adapted to enclose the apparatus according to any preceding claim.
16. An electro-mechanical electricity consumption meter according to Claim 14 or Claim 15 wherein the sealed housing is adapted to include a window such that the rotatable component is visible through the housing from under the sealable terminal cover.
17. An apparatus for use with an electro-mechanical electricity consumption meter substantially as hereinbefore described or substantially as illustrated by way of reference to the accompanying drawings.