US 5,587,520 AGranted

Thermal conductivity detector

AssigneeHewlett-Packard Company

InventorRobert P. Rhodes

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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.

Claims7

Dependent claims

A thermal conductivity detector for detecting the thermal conductivity of a sample fluid, comprising:

a cavity wall defining a cavity for receiving a quantity of the sample fluid, said cavity wall having a cavity wall temperature;
a sensor located in said cavity and connected as a first element in a bridge circuit configuration, said sensor having a sensor resistance which is dependent on a temperature of said sensor;
a selectable resistor having a selectable resistance in response to a resistor control signal, the selectable resistor being connected in said bridge circuit configuration as a second element wherein the resistance of said selectable resistor controls the temperature of said sensor;
signal providing means, connected to said sensor, for providing an output signal which is related to a change in the power delivered to said sensor and thereby representative of the thermal conductivity of the sample fluid;
heating means for providing a temperature sense signal representative of the cavity wall temperature and for controlling the cavity wall temperature in response to a heating control signal;
and
a controller connected to said selectable resistor and said heating means for;
a. receiving said temperature sense signal,
b. determining a desired cavity wall temperature, a desired sensor temperature, and a respective temperature differential therebetween;
c. and in response, providing said heating control signal to effect said desired cavity wall temperature and providing the resistor control signal to effect the selected resistance of the selectable resistor so as to establish the desired temperature of the sensor;
whereby the desired temperature differential may be established between the temperature of the sensor and the temperature of the cavity wall.

8 more elements

Dependencies are inferred from the claim text.