Method and apparatus for RMS current approximation

Details Method and apparatus for RMS current approximation Method and apparatus for RMS current approximation

1993-08-11

1995-09-12

Hoff, Marc S.

Electricity: electrical systems and devices

Safety and protection of systems and devices

With specific current responsive fault sensor

361 79, 361 18, H02H 326

Patent

active

054502683

ABSTRACT:
A method and apparatus provides for a measurement technique which approximates the true rms value of a current waveform. The technique involves converting the current waveform to a voltage by rectification and determining the peak value and the average value of the resultant voltage. A summing circuit combines the two values at a predetermined ratio to create a DC voltage that is approximately equal to the rms value of the input currents. The DC voltage output is suitable for a wide range of applications. A combination of the approximation circuit with a time integrating circuit and a level detecting circuit produces a low cost solid state overload relay in a preferred embodiment of the invention. Other uses include metering and use as a current feedback control signal for controlling PWM inverters and the like.

REFERENCES:
patent: 3573604 (1971-04-01), Lundgreen
patent: 4345288 (1982-08-01), Kampf et al.
patent: 4658323 (1987-04-01), Dougherty
patent: 5220478 (1993-06-01), Innes et al.

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