Thermal conductivity detector circuit
AssigneeBodenseewerk Perkin-Elmer & Co., GmbH
InventorHelfried Piesche
Life of this patent
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Abstract
There is disclosed a circuit which supplements a bridge-type detector circuit in order to minimize non-linearities resulting in measurements of thermal conductivity by such type bridges. An auxiliary voltage source is described which has an adjustable output voltage which is servoed to follow the output voltage of a differential amplifier which is connected to the output of the bridge. When the bridge is balanced at the desired operating temperature, the auxiliary supply is switched in and this voltage now controls the current supplied to the bridge instead of the differential amplifier output voltage thus eliminating the cause of the non-linearities at the point of measurement.
Claims6
In a thermal conductivity detector circuit including a measuring bridge having respective pairs of filaments electrically connected in corresponding legs of said bridge, said measuring bridge positioned in one leg of a second bridge circuit, an adjustable resistor electrically connected in the leg of said second bridge opposite the leg containing said measuring bridge circuit, a differential amplifier connected to the output terminals of said second bridge, current control means connected in circuit between a supply voltage source and said second bridge for supplying current to said second bridge, the output voltage of said differential amplifier controlling the flow of current through said current control means whereby said second bridge becomes balanced, wherein the improvement comprises an auxiliary voltage source for controlling said current control means including:
- a. a second voltage supply having an adjustable output voltage;
- b. means for electrically comparing the adjustable output voltage of said second supply to the output of said differential amplifier;
- c. means responsive to the output of said comparing means for varying the output voltage of said second voltage supply;
- d. means for disconnecting said differential amplifier output and electrically connecting said adjustable output voltage of said supply to said current control means when said adjustable output voltage equals the output voltage of said differential amplifier;
- and
- e. means for interrupting said means for varying the voltage supply when said adjustable output voltage equals the output of said differential amplifier.
Dependencies are inferred from the claim text.