Electronic watt and/or watthour measuring circuit having active load terminated current sensor for sensing current and providing automatic zero-offset of current sensor DC offset error potentials
First Claim
1. An electronic measuring circuit for measuring alternating current electrical energy, said measuring circuit having an active load terminated input current transformer with active load termination for deriving an input signal representative of the current supplied from a source of alternating current electric energy to be monitored and a voltage transformer for deriving an input signal representative of the voltage supplied from the source, electronic multiplier circuit means for multiplying together the signal representative of the current and the signal representative of the voltage, said electric multiplier circuit means comprising CMOS type electronic switches having first and second inputs and an output, comparator circuit means supplied with an input reference signal and with either of the signals representative of the current or voltage as a second input and for deriving at the output thereof a pulse width modulated signal representative of either the current or voltage that is supplied to the first input to said multiplier circuit means, the other of said current or voltage signals being supplied to the second input terminal of the multiplier circuit means, and means for deriving at the output from said multiplier circuit means an output amplitude modulated and pulse width modulated product signal that is representative of the product of the current and voltage supplied from the source of electric energy with any DC offset error caused by the active load terminated input current transformer being automatically zeroed out.
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Accused Products
Abstract
An electronic watt and kilowatt hour measuring circuit susceptible of being fabricated for the most part in solid state semiconductor monolithic integrated circuit form is provided. The electronic measuring circuit uses an active load terminated current transformer sensor for sensing alternating load current and a voltage transformer for sensing the alternating current voltage supplied from a source of alternating current electric energy being monitored. The output of the active load terminated current sensor transformer has an inherent DC-offset error voltage added to the alternating voltage which is proportional to the current being measured. This DC-offset error voltage is caused by the operational amplifier employed in the active load terminated current transformer sensor. By using time division multiplier circuits employing CMOS electronic switches as a means for multiplying the current and voltage signals together, the DC-offset error caused by the active load terminated current transformer sensor automatically will be zeroed out. The circuit can be employed as a straightforward multiplier to derive an output indication of instantaneous watts, or can be employed together with an analog-to-digital pulse rate converter for obtaining kilowatt hours of electrical energy consumed, and can be further modified to provide both instantaneous watts and kilowatt hours measurements, by appropriate design of the circuit together with system-wide correction of any DC-offset error voltages produced within the measuring circuit.
97 Citations
24 Claims
- 1. An electronic measuring circuit for measuring alternating current electrical energy, said measuring circuit having an active load terminated input current transformer with active load termination for deriving an input signal representative of the current supplied from a source of alternating current electric energy to be monitored and a voltage transformer for deriving an input signal representative of the voltage supplied from the source, electronic multiplier circuit means for multiplying together the signal representative of the current and the signal representative of the voltage, said electric multiplier circuit means comprising CMOS type electronic switches having first and second inputs and an output, comparator circuit means supplied with an input reference signal and with either of the signals representative of the current or voltage as a second input and for deriving at the output thereof a pulse width modulated signal representative of either the current or voltage that is supplied to the first input to said multiplier circuit means, the other of said current or voltage signals being supplied to the second input terminal of the multiplier circuit means, and means for deriving at the output from said multiplier circuit means an output amplitude modulated and pulse width modulated product signal that is representative of the product of the current and voltage supplied from the source of electric energy with any DC offset error caused by the active load terminated input current transformer being automatically zeroed out.
Specification