Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Nonlinear
Patent
1994-01-27
1995-09-26
Wieder, Kenneth A.
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Nonlinear
324119, 324130, 374171, G01R 1922, G01R 130
Patent
active
054536820
ABSTRACT:
A meter measures a voltage across a quasi-diode, the voltage caused by a current flowing through a resistance which changes substantially exponentially with changes in a medium being sensed. The meter comprises a logarithmic current measuring circuit coupled to the resistance to provide a measurement output that is a logarithmic function of the current flowing through the sensing resistance. A switchable current source is controlled by a switching circuit to repetitively output first and second current values. A reference logarithmic circuit is connected to the switchable current source and is physically coupled to the logarithmic measuring circuit so as to be maintained at a substantially equal temperature value. The logarithmic reference circuit manifests a first voltage in response to the first current value and a second voltage in response to the second current value, both voltage values dependent upon the temperature of the logarithmic reference circuit. A processor controls the switchable current source to operate at a repetition rate which assures that the first and second current values occur sufficiently rapidly so that the first and second voltages are manifest before the temperature value has had an opportunity to substantially vary. The processor derives from the first voltage, second voltage, and the measuring circuit output, a corrected output that eliminates meter temperature affects.
REFERENCES:
patent: 4513245 (1985-04-01), Yokoyama
Hinrichs Karl
Mohtashemi Abdollah
Bowser Barry C.
Hosmer Bruce E.
Newport Electronics, Inc.
Reiter Howard S.
Wieder Kenneth A.
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