Electricity: measuring and testing – Testing and calibrating electric meters
Patent
1993-09-28
1996-07-23
Karlsen, Ernest F.
Electricity: measuring and testing
Testing and calibrating electric meters
324130, G01R 3504
Patent
active
055393047
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
This invention concerns the calibration of apparatus designed to measure electrical power, methods and apparatus therefor.
BACKGROUND OF THE INVENTION
It is known to measure voltage and current to ascertain the power consumption from a supply typically an alternating current supply, by generating signals corresponding to the voltage and current, producing a product of the two signals and integrating the result over a period of time.
In recent years development work has been concentrated on meters incorporating solid state devices for performing some of the computations. Potentially such devices allow more accurate measurement than older electromechanical designs of meter and will also enable remote reading to be incorporated more readily into such meters.
After manufacture (or refurbishment) it is necessary to calibrate such meters relative to some standard--usually by comparing the power reading obtained using the meter under test against that measured by a "standard" meter, and adjusting the former as appropriate.
It is an object of the present invention to provide power measuring apparatus which can be readily calibrated using a standard.
It is a further object of the invention to provide a method of calibration for power measuring apparatus and apparatus for calibrating said meters.
SUMMARY OF THE INVENTION
According to the present invention in power measuring apparatus adapted to produce an output signal proportional to the product of a supply voltage and current flowing through a load connected thereto, in which a first signal is derived proportional to the supply voltage and a second signal is derived proportional to the load current, so that a product signal can be produced, and wherein the product signals are accumulated in a first register to produce a unit power pulse when a predetermined value has been accumulated in the register, which unit power pulses are in turn accumulated in a power register to indicate total power measured, apparatus for calibrating the power measuring apparatus against a standard meter comprises:
(1) circuit means responsive to unit power pulses (or pulses derived therefrom) from the standard meter for entering said pulses into a second register for accumulating unit power pulses from the standard meter,
(2) measuring means for storing a value N with which the accumulating value in the said second register can be compared,
(3) pulse generating circuit means for generating a calibration signal when the value in the second register equals the value N in the memory means,
(4) divider means for dividing the value in the said first register by the value N to produce a reference value in response to the generation of a calibration signal, and
(5) means for retaining the said reference value for future reference within the meter under test, as the said predetermined value with which the accumulating value in the first register is to be compared for generating unit power pulses by that meter.
Where the unit power pulses from the standard meter are generated at an appropriate rate and are available at an output socket, the said calibrating circuit means may simply comprise conductor means for connecting the said output socket to an input socket on the meter under test, for conveying the unit power pulses from the standard meter to the said second register in the meter under test.
Where as is more likely the standard meter produces at the output socket more unit power pulses per KWH than are generated by the circuits of the meter under test when measuring the same power (typically 500 times as many), the calibrating circuit means preferably also includes divider means to produce one pulse for every n pulses from the standard meter, (where n may for example be 500).
Where the meter under test includes an optical communication port (such as one operating in accordance with the GIMEX protocol), the circuit means may comprise a housing containing a light source, conductor means for connecting to the said output socket to convey unit power pulses to the housi
REFERENCES:
patent: 4464723 (1984-08-01), Chartier
patent: 4623976 (1986-11-01), Carp et al.
patent: 4665358 (1987-05-01), Bullock et al.
patent: 4788620 (1988-11-01), Scott
patent: 4949029 (1990-08-01), Cooper et al.
King Roger H.
Payne Kenneth
Watson David A.
Ampy Automation - Digilog Limited
Karlsen Ernest F.
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