Circuit for heating and sensing with a single element
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United States of America Patent
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Mar 24, 1992
Grant Date -
N/A
app pub date -
Jan 4, 1991
filing date -
Jan 4, 1991
priority date (Note) -
Expired
status (Latency Note)
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Abstract
A circuit for differential calorimetry includes a pair of resistance elements in a bridge circuit. Separate DC heating currents are effected in each element by high impedance current sources. An AC voltage is applied to the bridge. In measuring AC differental voltage between the elements, the DC is filtered out. The filtered AC differential voltage is fed back to effect a current differential between the heating currents to null the differential temperature causing the differential voltage. A similarly filtered average AC voltage on the elements is compared with a reference voltage, and the resulting error voltage is fed back to control the average of the heating currents. A very high impedance current source includes a voltage-current transducer with an output of a heating current passed through a monitor resistor, with matched resistances from both sides of the monitor connected back to positive and negative inputs to the transducer, and a control voltage applied across the inputs.
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