NZ617310B2 - Electrical measurement apparatus having a detector providing an identification signal and corresponding method - Google Patents

Abstract

Disclosed is an electrical measurement apparatus for measuring an electrical parameter of a device. The apparatus is comprised of a meter and a detector, wherein the detector is arranged to detect the electrical parameter and transmit a measurement signal representing the electrical parameter to the meter. The detector is also arranged to provide to the meter an identification signal for identifying the detector to the meter. The identification signal is representative a measurable value of a component (Ri) of the detector, for example a resistance of a resistor. This signal may also be used to determine the rating of the detector, in particular the rating of a transformer or transducer of the detector, to ensure accurate readings are made by the meter and detector combination. e meter. The detector is also arranged to provide to the meter an identification signal for identifying the detector to the meter. The identification signal is representative a measurable value of a component (Ri) of the detector, for example a resistance of a resistor. This signal may also be used to determine the rating of the detector, in particular the rating of a transformer or transducer of the detector, to ensure accurate readings are made by the meter and detector combination.

Description

ELECTRICAL MEASUREMENT APPARATUS AND METHOD Field of the Invention The present invention relates to an electrical measurement apparatus for measuring an electrical parameter of a device; a detector for use in the measurement of an electrical parameter of a device; and a method of measuring an electrical parameter of a device. For example the invention relates to an electrical measurement apparatus and method, and is concerned particularly with an electrical measurement apparatus and method suitable for use in an electrical metering system.

Background of the Invention In commercial premises particularly, the electricity usage of several devices or appliances, hereinafter referred to generally as loads , is often monitored using separate meters for each load. In such cases, in order to derive valuable data about the energy usage of each load it is necessary to collate metered values manually, and subsequently enter the data manually on a computer for processing.

A previously considered example of electricity meter brings together a fixed number of metering units and combines them in a unitary housing, together with a common visual display and processing means to manipulate and present the data collected by the individual metering units. Signal wires are used to carry the measurement signals from current detectors such as current transducers or transformers located locally at each load. The combined multi-meter load is particularly suited to modern premises in which the electrical supply enters the building at a single location, and is controlled from a single control panel.

Modern electronic electricity meters are designed to measure a variety of load types and sizes.

Current inputs to the meters are standardised to accept a specific signal type and value which represents a larger measured value of current at the load. A range of external current transformers or transducers are used to convert the detected primary current into a representative secondary signal that may be measured by the metering circuit.

For example a meter may accept a 0.333 Vac signal which represents any nominal primary current determined by the selection of an appropriate external current transducer.

Typical external transducers may be of a split or toroidal type such as 100 Amp/0.333V or 500 Amp/0.333V.

When a metering system is installed the user must select the most appropriate transformers/transducers for the measured load dependent on the maximum current that the load would draw in normal operation. These devices may be physically located some distance away from the meters themselves. For example the transformers/transducers may be located in a separate switch enclosure or in a different room. Many meters may be installed together and may be connected to different ranges of transformers/transducers.

During commissioning of the metering system the installing engineer must program the individual meters to provide readings that are scaled in proportion to the specific transformers or transducers to which they are respectively connected. This often presents the practical problem of identifying which set of wires is associated with which remotely located transducer/transformer.

To assist with this the installing engineer carefully labels the wires with the load size and type before installing the transformers/transducers. If this stage is forgotten or performed inaccurately it may be necessary to remove the installation and start again.

If mistakes are made during installation or commissioning these may remain undetected for long periods, and indeed may never be picked up. However, such mistakes can be costly. For example if a 200 Amp transducer is connected to a meter which is programmed to scale for a 150 Amp transducer, when 200 Amps is detected by the transducer the secondary signal will provide 0.333 V to the meter. The meter is scaled to assume that 0.333 V is equivalent to 150 Amps so will display readings which are in error by the ratio 150/200 (i. e. a 25% error). This discrepancy may not be obvious to the meter reader, and the power/energy readings accepted may lead to errors in billing and possibly the taking of inappropriate management decisions based on the erroneous data. Larger errors in scaling may be less likely to escape detection.

US 2008/0284614 describes a power monitoring system for monitoring characteristics of power transmitted through one or more power lines, comprising a meter base and multiple option modules. The meter base includes a processor and associated circuitry for processing signals derived from sensors coupled to said power lines and producing output signals representing selected characteristics of the power transmitted through the power lines, and a housing containing the processor and the associated circuitry and having a first surface adapted to be mounted on a DIN rail, and a second surface containing multiple connectors for receiving multiple modules and electrically connecting the modules to the processor and the associated circuitry.

US 4,963,820 describes an energy meter composed of a meter chassis having a transducer connected to sense energy usage and to provide an output having a fixed relation to the sensed energy usage, a replaceable register connectable to the transducer for converting the output provided by the transducer into a readable energy usage indication, a transducer identifying unit secured to the chassis and coded to identify the fixed relation between the transducer output and the sensed energy usage, and a transducer sensing unit secured to the register for coupling with the transducer identifying unit when the register is connected to the transducer.

JP 2005 038492 describes an identification method for mounting parts of electronic device, and an electronic device which can identify mounting parts, comprising an identification resistor having different resistance values for each version information of a circuit board internally connected between the first pin and the third pin which are empty terminals on equipment function of an interface section of the FDD drive. An identification circuit including the resistor is formed by a tester through the first pin and the third pin. The resistor is identified based on the output result from the identification circuit, and based on the identification result, version information of a circuit board is specified and the circuit board is identified.

It is generally desirable to overcome or ameliorate one or more of the above described difficulties, or to at least provide a useful alternative.

Summary of the Invention According to the present invention there is provided electrical measurement apparatus for measuring an electrical parameter of a device, the apparatus comprising a meter and a detector, wherein the detector is arranged to detect the electrical parameter transmit a measurement signal to the meter, which signal is representative of the detected electrical parameter, and wherein the detector is arranged to provide to the meter an identification signal for identifying the detector to the meter, and characterised in that the detector comprises a component (Ri) having a measurable value, which measurable value serves as the identification signal.

According to the present invention, there is also provided a detector for use in the measurement of an electrical parameter of a device, wherein the detector is arranged to detect the electrical parameter and transmit a measurement signal to a meter, which signal is representative of the detected electrical parameter, wherein the detector is arranged to provide to a meter an identification signal for identifying the detector to the meter, and characterised in that the detector comprises a component (Ri) having a measurable value, which measurable value serves as the identification signal.

According to the present invention, there is also provided a method of measuring an electrical parameter of a device, the method comprising detecting the electrical parameter using a detector, and transmitting a measurement signal to a meter, which signal is representative of the detected electrical parameter, the method further comprising providing to the meter an identification signal for identifying the detector to the meter, and characterised in that the detector comprises a component ( Ri) having a measurable value, which measurable value serves as the identification signal.

Preferred embodiments of the present invention aim to address at least some of the aforementioned shortcomings in the prior systems.

In a preferred arrangement the identification signal may be derived from a component in the detector or in an electrical connection between the detector and the meter, or a component associated with either.

The identification signal may be derived from the presence and/or value of the component. Preferably the detector comprises a component having a measurable value, which measurable value serves as the identification signal.

The detector may be arranged to communicate with the meter wirelessly. Alternatively, or in addition, the detector may be connected to the meter by wire. In a preferred arrangement the detector comprises a resistive element, the value of which is measured by the meter to determine the identity of the detector.

The meter may comprise identification means, which preferably comprises a circuit, which is arranged in use to receive the identification signal and to use it to identify the detector.

The detector may be according to any statement herein.

The electrical parameter to be measured may comprise electrical current and/or power.

The method may comprise identifying the detector by detection and/or measurement of a component in or associated with the detector, the presence and/or value of which component serves to identify the detector.

Brief Description of the Drawings Preferred embodiments of the present invention are hereafter described, by way of non-limiting example only, with reference to the accompanying drawings, in which: Figure 1 shows schematically a detector, in the form of a current transducer, for use in apparatus; and Figure 2 is a schematic circuit diagram of the current transducer of Figure 1.

Detailed Description of Preferred Embodiments of the Invention Turning to Figure 1, there is shown, generally at 10, a three - phase toroidal current transducer comprising a cuboid detector body 12, having three cylindrical passages 14 each for receiving a single phase cable of a three phase load (not shown). Each of the three passages 14 has an embedded toroidal winding (not shown) which is used to detect a current in the load cable (also not shown).

Signals representing the current in each of the three individual load cables are sent to a meter (not shown), which may be located remotely. The signals are transmitted along a multi-core signal cable 16, which has a standard connector 18 for a plug-in connection to the meter.

As will be described below, one of the wires in the multi- core signal cable 16 is connected to a component in the transducer 10 that identifies the rating of the transducer, so that the meter can determine this automatically when the signal cable is plugged in.

Figure 2 shows the circuit of the transducer 10. The three currents in the three single phase load cables are represented by I1, I2 and I3, and the three toroidal windings are represented by T1, T2 and T3. In each case a burden resistor, respectively Rb1, Rb2 and Rb3 is connected between ground and a signal line to produce voltage signals V1, V2 and V3 for supply via cable 16 to the meter. Other wires in the cable 16 include a ground connection V0 and a connection to an identification resistor Ri, itself connected to ground.

The value of the identification resistor Ri can be determined by a resistor detector circuit in the processor in the meter, and this is used to set the rating of the transducer 10 which the meter uses when calculating the current in the load cables. For example, the meter may be programmed to determine that an identification resistor having a value of 2 k means that the transducer is rated at 100A/0.333V, which means that if a voltage of 0.333V is measured at any of Vi1, Vi2 or Vi3 this represents a current of 100A in the respective load cable.

Of course the identification component need not be a resistor. With appropriate circuitry the meter could determine the rating of the transducer by detecting the value of a different type of component. However a resistor provides a particularly inexpensive solution.

Furthermore the current detector need not be a transducer, but could for example be a transformer. In such a case the circuit would be different as there would be two voltage identification lines for each of the single phase currents. Again a simple resistor could be used as the identification component.

The example given above is of a three phase load measurement, but the invention is equally applicable to a single phase load, which would require the use of fewer wires in the cable 16.

During a powering up of the meter the resistor detector circuit in the meter determines the value of the resistor and automatically configures the meter scaling and calibration to suit the transducer connected, without error or ambiguity to save time during commissioning.

The standard connector 18 is easily plugged into the meter, which also saves time during installation and commissioning of the meter system.

Embodiments of the invention aim to add a low cost component to the transducer or set of transducers which is detected by an additional measurement circuit in the meter.

A resistor is sufficient for this purpose, and adds negligible cost to the transducer. Resistor values can be accurately measured by the meter to determine which transducer is fitted at the end of the secondary wires.

The accuracy of the resistor detector could be sufficient as to differentiate between many primary scaling factors and, if required, transducer types. An example of how this could work is laid out in the table shown below: Resistor CT Primary Assumed CT Type Assumed 1k Type A (S mall Split CT) 1.2k Type B (M edium Slit CT) 1.3k 50 Amp Type C ( L arge Split CT) 1.4k Type D ( S mall Ring CT) 1.5k Type E (L arge Ring CT) 2k Type A (S mall Split CT) 2.2k Type B (M edium Slit CT) 2.3k 100 Amp Type C (L arge Split CT) 2.4k Type D (S mall Ring CT) 2.5k Type E (L arge Ring CT) 2k Type A ( S mall Split CT) 3.2k Type B ( M edium Slit CT) 3.3k 150 Amp Type C (L arge Split CT) 3.4k Type D (S mall Ring CT) 3.5k Type E ( L arge Ring CT) 4k 200 Amp Type A ( S mall Split CT) 4.2k Type B ( M edium Slit CT) 4.3k Type C (L arge Split CT) 4.4k Type D (S mall Ring CT) 4.5k Type E ( L arge Ring CT) 5k Type A (S mall Split CT) .2k Type B ( M edium Slit CT) .3k 300 Amp Type C (L arge Split CT) .4k Type D (S mall Ring CT) .5k Type E (L arge Ring CT) Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance, it should be understood that the applicant claims protection in respect of any patentable feature or combination of features referred to herein, and/or shown in the drawings, whether or not particular emphasis has been placed thereon.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word comprise, and variations such as comprises and comprising, will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

Claims (7)

Claims Defining the Invention

1. Electrical measurement apparatus for measuring an electrical parameter of a device, the apparatus comprising 5 a meter and a detector, wherein the detector is arranged to detect the electrical parameter and transmit a measurement signal to the meter, which signal is representative of the detected electrical parameter, wherein the detector is arranged to provide to the meter an identification signal 10 for identifying the detector to the meter, and characterised in that the detector comprises a component (Ri) having a measurable value, which measurable value serves as the identification signal. 15

2. Electrical measurement apparatus according to claim 1, wherein the detector is arranged to communicate with the meter wirelessly.

3. Electrical measurement apparatus according to claim 1 20 or 2, wherein the detector may be connected to the meter by wire.

4. Electrical measurement apparatus according to any of the preceding claims, wherein the detector comprises a 25 resistive element, the value of which is measured by the meter to determine the identity of the detector.

5. Electrical measurement apparatus according to any of the preceding claims, wherein the meter comprises 30 identification means, which comprises a circuit arranged in use to receive the identification signal and to use it to identify the detector.

6. A detector for use in the measurement of an electrical parameter of a device, wherein the detector is arranged to detect the electrical parameter and transmit a 5 measurement signal to a meter, which signal is representative of the detected electrical parameter, wherein the detector is arranged to provide to a meter an identification signal for identifying the detector to the meter, and characterised in that the detector comprises a 10 component (Ri) having a measurable value, which measurable value serves as the identification signal.

7. A method of measuring an electrical parameter of a device, the method comprising detecting the electrical 15 parameter using a detector, and transmitting a measurement signal to a meter, which signal is representative of the detected electrical parameter, the method further comprising providing to the meter an identification signal for identifying the detector to the meter, and 20 characterised in that the detector comprises a component (Ri) having a measurable value, which measurable value serves as the identification signal.