US 4,627,269 A · Method of, and apparatus for, detecting reducing gases in a gas mixture

Abstract

Reducing gases can be detected in a gas mixture to be investigated, particularly in air, with high sensitivity and precision by means of a gas detector. The gas detector comprises a gas sensor which is arranged within a measuring chamber. The temperature of the gas sensor can be continuously increased according to a predetermined pattern from a starting value to an upper threshold value and can be subsequently decreased again to the starting value according to the same or according to a different pattern. There are provided at least two such heating cycles. Simultaneously therewith the gas mixture to be investigated, which is present in the measuring chamber, is periodically exchanged against a pure reference gas which is contained in a reference chamber. A selected property, such as the electrical conductivity of the gas sensor is thereby periodically changed. The temporal variation of this periodically varying electric conductivity can be detected in an evaluation circuit arrangement and/or evaluated for determining the concentration and/or the nature of the reducing gases which are present in the gas mixture to be investigated.

Claims121

Dependent claims

A method of detecting at least one reducing gas in a gas mixture to be investigated, particularly in air, said method comprising the steps of:

selecting a gas sensor containing a metal oxide semiconductor possessing a selected property which is dependent on the presence of said at least one reducing gas in said gas mixture;
cyclically varying the temperature of said gas sensor by continuously increasing said temperature from a starting value to an upper threshold value and subsequently decreasing said temperature from said upper threshold value to said starting value;
cyclically exposing said gas sensor to said gas mixture to be investigated and at least partially to a reference gas containing a smaller amount or none of said at least one reducing gas, whereby said selected property of said metal oxide semiconductor is subject to a cyclical variation as a function of time;
and
measuring said cyclical variation of said selected property of said metal oxide semiconductor.

2 more elements

An apparatus for detecting at least one reducing gas in a gas mixture to be investigated and comprising:

a gas detector defining a measuring chamber;
said gas detector containing a gas sensor which comprises a metal oxide semiconductor possessing a selected property which is dependent upon the presence of said at least one reducing gas in said gas mixture to be investigated;
heating means for heating said gas sensor to a predetermined temperature;
a reference chamber connected to said measuring chamber;
said reference chamber being closed towards the external atmosphere and being provided with gas displacement means;
an evaluation circuit arrangement;
said gas sensor being operatively connected to said evaluation circuit arrangement and generating output signals which are supplied to said evaluation circuit arrangement;
said gas displacement means constituting a displaceable piston;
said displaceable piston, during a suction phase of its operation, drawing in said gas mixture to be investigated and passing said gas mixture through said gas sensor in a heated state thereof and practically passing said gas mixture over said heated gas sensor, and said displaceable piston thereafter forcing back the thus obtained gas mixture;
said gas sensor defining a surface;
said gas mixture to be investigated and present in said measuring chamber substantially completely contacting said surface of said gas sensor by means of said displacement of said displaceable piston in order to convert as far as possible said at least one reducing gas at said surface of said gas sensor and to pass, during a venting phase of the operation of said displaceable piston, a gas mixture which is substantially free of said at least one reducing gas along said gas sensor and through said measuring chamber, when said displaceable piston is forced back;
a microswitch;
two power sources operatively connected to said heating means and delivering predetermined different heating voltages;
and
said microswitch being operated during each stroke of said displaceable piston such that said different heating voltages are alternatingly supplied from said two power sources to said heating means.

12 more elements

An apparatus for detecting at least one reducing gas in a gas mixture to be investigated and comprising:

a gas detector defining a measuring chamber;
said gas detector containing a gas sensor which comprises a metal oxide semiconductor possessing a selected property which is dependent upon the presence of said at least one reducing gas in said gas mixture to be investigated;
heating means for heating said gas sensor to a predetermined temperature;
a reference chamber connected to said measuring chamber;
said reference chamber being closed towards the external atmosphere and being provided with gas displacement means;
an evaluation circuit arrangement;
said gas sensor being operatively connected to said evaluation circuit arrangement and generating output signals which are supplied to said evaluation circuit arrangement;
said measuring chamber possessing a predetermined volume;
said reference chamber possessing a predetermined volume;
and
said predetermined volume of said measuring chamber and said predetermined volume of said reference chamber being matched to each other such that during each said suction phase a first sample of said gas mixture to be investigated is drawn into said measuring chamber through said inlet opening thereof and that during each said venting phase at least a portion of said gas mixture to be investigated leaves said measuring chamber through said inlet opening thereof.

8 more elements

Dependencies are inferred from the claim text.

Method of, and apparatus for, detecting reducing gases in a gas mixture

Life of this patent

Method of, and apparatus for, detecting reducing gases in a gas mixture

Life of this patent

Abstract

Claims121