Measuring and testing – Gas analysis – By thermal property
Patent
1995-09-29
1996-12-24
Williams, Hezron E.
Measuring and testing
Gas analysis
By thermal property
732025, 7320411, 7320415, G01N 2518
Patent
active
055875203
ABSTRACT:
A thermal conductivity detector includes a cavity wall defining a cavity for receiving a quantity of the sample fluid, the cavity wall being subject to a cavity wall temperature, and a sensor located in the cavity and connected as a first element in a bridge circuit configuration. The sensor exhibits a resistance which is dependent on a temperature of the sensor. A variable resistor having a selectable resistance in response to a control signal is connected in the bridge circuit configuration as a second element. A signal providing means, connected to the balance nodes of the bridge circuit configuration, provides a first signal which is related to a change in resistance of the sensor and thereby representative of the sensor temperature. Means for sensing the temperature of the cavity wall provides a temperature sense signal to a controller, which in response provides a heating control signal to a cavity wall heating means. The controller also determines the cavity wall temperature and in response causes the variable resistor to achieve a selected resistance value that will cause the sensor resistance to change. The temperature of the sensor is thereby set so as to accurately and reliably establish a selectable, predetermined temperature differential between the sensor and the cavity wall.
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Dudley Mark Z
Hewlett--Packard Company
Politzer Jay L.
Williams Hezron E.
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