THERMAL CONDUCTIVITY SENSOR

Abstract

A sensor for determining the thermal conductivity of a fluid comprising a sensing module located within a housing having inlet and outlet ports for a fluid under test, the sensing module comprising a reference base surface and a sensing element spaced therefrom and having measure and reference sections, and there being provided electrical power monitoring means for monitoring the power through the measure and reference sections in order to generate a signal indicative of the power difference due to thermal conductivity through the fluid. The sensing element is a thick film printed disc with measure and reference resistors printed on it. All changes in the fluid are common to both the measure and reference sections except for the thermal conductivity of the fluid itself.

Description

In order that the present invention be more readily understood, an embodiment thereof will now be described by way of example with reference to the accompanying drawings, in which:—

FIG. 1 shows a diagrammatic view of part an embodiment of the present invention;

FIG. 2 shows a diagrammatic view of a part of the embodiment shown in FIG. 1, together with a plan view of a thick film printed disc; and

FIG. 3 shows a graph of power difference against thermal conductivity for the embodiment.

Claims

1. A sensor for determining the thermal conductivity of a fluid comprising a sensing module located within a housing having inlet and outlet ports for a fluid under test, the sensing module comprising a reference base surface and a sensing element spaced therefrom and having measure and reference sections, and there being provided electrical power monitoring means for monitoring the power through the measure and reference sections in order to generate a signal indicative of the power difference due to thermal conductivity through the fluid.

2. The sensor according to claim 1, wherein the sensing element is a thick film printed disc with measure and reference resistors printed on it.

3. The sensor according to claim 1, wherein the monitoring means includes a Wheatstone bridge, whose output constitutes the signal.

4. The sensor according to claim 1, further comprising a diffusive element, wherein the diffusive element is used to control a fluid diffusion rate onto the sensing element.

5. The sensor according to claim 1, wherein the sensing element is a thick film printed disc, wherein a thickness and thermal conductivity of the substrate material is chosen so as to optimize a sensitivity and time response of the sensing element.

6. The sensor according to claim 5, wherein the disc is provided with thermal breaks between the measure and reference sections in order to enhance sensitivity.

7. The sensor according to claim 1, wherein the sensing element is a thin film element.

8. The sensor according to claim 1, wherein a thermistor or Peltier cooler is used for the measure and reference sections of the sensing element.

9. A sensor according to claim 1, wherein multiple measure and reference sections are used to obtain a larger signal or signal averaging.

10. The sensor according to claim 2, wherein the sensing element is a thick film printed disc, wherein a thickness and thermal conductivity of the substrate material is chosen so as to optimize a sensitivity and time response of the sensing element.

11. The sensor according to claim 3, wherein the sensing element is a thick film printed disc, wherein a thickness and thermal conductivity of the substrate material is chosen so as to optimize a sensitivity and time response of the sensing element.

12. The sensor according to claim 4, wherein the sensing element is a thick film printed disc, wherein a thickness and thermal conductivity of the substrate material is chosen so as to optimize a sensitivity and time response of the sensing element.