Electricity: measuring and testing – Conductor identification or location – Inaccessible
Patent
1978-03-06
1979-07-10
Krawczewicz, Stanley T.
Electricity: measuring and testing
Conductor identification or location
Inaccessible
G01R 2702
Patent
active
041609492
ABSTRACT:
An auto-zeroed ohmmeter is comprised of a current source having first and second leads for connection to respective terminals of an unknown resistor to generate first and second voltages at the terminals. A sensing circuit having third and fourth leads connects to the terminals of the unknown resistor and scales the first and second voltages to third and fourth voltages respectively. A ramp generator circuit is coupled to the sensing circuit and generates a ramp voltage with a slope proportional to the difference between the fourth voltage and a multiple of the third voltage. This ramp is generated for a time period of predetermined duration to thereby produce a reference point voltage at the end of the time period. Coupled to the ramp generator are circuits for reducing the reference point voltage at a predetermined rate, for measuring the time interval required to reduce the reference point voltage to the multiple of the third voltage, and for multiplying the measured time interval by a predetermined constant to compute resistance.
REFERENCES:
patent: 3447075 (1969-05-01), Williams, Jr. et al.
patent: 3895376 (1975-07-01), Uchida
California Instruments Corporation
Krawczewicz Stanley T.
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