Detection and analysis of gases or vapours

Claim 2

Apparatus for detecting or analysing a gas condition comprising a semiconductor material that exhibits an exhaustion region, a constant current control circuit connected to said semiconductor material for heating said semiconductor material, means controlling the constant current control circuit and maintaining the temperature of the semiconductor material, in the absence of the gas condition to be detected of analysed, at a value in the vicinity of one end of its exhaustion region, and means for measuring change in voltage drop across the semiconductor material, which change, in the presence of the gas condition to be detected or analysed, comprises a gas signal component, resulting from the change in conductivity of the semiconductor material in the presence of the gas condition, and a temperature signal component, resulting from the change in conductivity of the semiconductor material on change in the maintained temperature of the material imposed by the constant current control circuit when the conductivity of the material changes.

Claim 3

Apparatus according to claim 1, in which the means for measuring changes in temperature comprises means for measuring the potential drop across the semiconductor material.

Claim 4

Apparatus according to claim 1, in which the semiconductor is an n-type material.

Claim 5

Apparatus for detecting the presence of a given gas in concentrations of less than about 1 part per million comprising, in combination: a semiconductor material which has a conductivity characteristic which exhibits a low temperature extrinsic negative resistance characteristic, a high temperature intrinsic negative resistance characteristic, and an exhaustion region between said low and high temperature regions which exhibits a more positive resistance characteristic than is exibited in said intrinsic and extrinsic regions; a constant current source connected in series with said semiconductor material for maintaining a constant current through said semiconductor material and for normally heating said semiconductor material to a temperature in said exhaustion region; means for exposing the surface of said semiconductor material to said given gas; and means for measuring the voltage drop across said semiconductor Material, whereby a change in the voltage drop across said semiconductor material indicates a change in the concentration of said given gas in the vicinity of the surface of said semiconductor material.

Claim 6

Apparatus for detecting the presence of a given gas in concentrations of less than about 1 part per million comprising, in combination: a semiconductor material which has a conductivity characteristic which exhibits a low temperature extrinsic negative resistance characteristic, a high temperature intrinsic negative resistance characteristic, and an exhaustion region between said low and high temperature regions which exhibits a more positive resistance characteristic than is exibited in said intrinsic and extrinsic regions; a constant current source connected in series with said semiconductor material for maintaining a constant current through said semiconductor material and for normally heating said semiconductor material to a temperature in said exhaustion region; means for exposing the surface of said semiconductor material to said given gas; and means for measuring the voltage drop across said semiconductor Material, whereby a change in the voltage drop across said semiconductor material indicates a change in the concentration of said given gas in the vicinity of the surface of said semiconductor material.

Claim 7

Apparatus according to claim 4 in which said semiconductor material is an n-type metal oxide.

Claim 8

Apparatus according to claim 5 in which said semiconductor material is zinc oxide, doped with a small percentage of platinum.