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US 5,098,196 AGranted
Circuit for heating and sensing with a single element
AssigneeThe Perkin-Elmer Corporation
InventorMichael J. O'Neill
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AssigneeThe Perkin-Elmer Corporation
InventorMichael J. O'Neill
Estimating the term…
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.
A circuit arrangement for providing heat and measuring temperature in an analytical instrument, comprising a resistance element having an element resistance responsive to temperature, first current means for effecting a heating current at a first frequency and being connected to direct the heating current through the resistance element and thereby heat the resistance element, second current means for effecting a sensing current at a second frequency and being connected to direct the sensing current through the resistance element so as to induce a sensing voltage responsive to the element resistance and thereby to temperature of the resistance element, and measuring means connected to the resistance element for determining a measured voltage on the resistance element, wherein the sensing current is effected simultaneously with the heating current, and the measuring means includes filtering means for filtering out the first frequency from the measured voltage so that the measured voltage is a filtered signal representative of the sensing voltage, whereby the filtered signal is representative of the temperature of the resistance element.
A circuit arrangement for providing heat and measuring differential temperature in an analytical instrument, comprising a pair of resistance elements each having a corresponding element resistance responsive to temperature, first current means for effecting at a first frequency separate heating currents and being connected to direct a corresponding one of the heating currents through each of the resistance elements and thereby heat the resistance elements, second current means for effecting at a second frequency separate sensing currents and being connected to direct a corresponding one of the heating currents through each of the resistance elements so as to induce on the resistance elements corresponding sensing voltages each being responsive to element resistance and thereby to temperature of a corresponding resistance element, and measuring means connected for measuring a voltage differential between the sensing voltages, wherein the sensing currents are effected simultaneously with the heating currents, and the measuring means includes filtering means for filtering out the first frequency from the voltage differential whereby the voltage differential is a filtered signal representative of differential temperature between the resistance elements.
Dependencies are inferred from the claim text.