US 5,510,269 AGranted

Infrared method and apparatus for measuring gas concentration including electronic calibration

AssigneeSensors, Inc.

InventorsKarl H. Black, Walter I. Armstrong

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Abstract

An automatic calibration technique for a gas analyzer includes applying electrical energy to a source that is different from the level used to detect gas concentration in order to produce a different level of radiation from that used to detect gas concentration. The different level is applied with a non-absorbing gas in the gas sample chamber. The detector output at the reduced level is resolved to a calibration factor. The instrument can be linearized by repeating the calibration procedure at multiple different levels of reduced source radiation. In one embodiment, source assembly (26) is provided that includes a plurality of infrared emitters (36) to which is applied modulated electrical energy in a timed sequence in order to produce output levels for three component gas concentrations. A filter (56) between each one of the sources (36) and a detector (50) pass radiation at an absorption line of one of the component gases.

Claims23

Dependent claims

A method of span calibrating a gas analyzer by determining at least one calibration factor, in which said analyzer detects at least one component gas in a sample by applying electrical energy at a given level to a radiation source in order to produce a given level of radiation having at least one absorption line of said at least one component gas, directing the given level of radiation along an optical path through a sample chamber, detecting radiation attenuated by absorption by said at least one component gas in said sample chamber at said at least one absorption line, and resolving said detected radiation attenuated by absorption and at least one calibration factor into component gas concentration, including:

filling said sample chamber with a gas that is non-absorbing of radiation at said at least one absorption line:
applying electrical energy at at least one known level that is different from said given level of energy to said source in order to produce at least one known level of radiation that is different from said given level of radiation;
detecting with said detector said at least one known level of radiation in order to produce at least one output signal;
and
determining at least one calibration factor as a function of said at least one output signal produced from said at least one known level of radiation that is different from said given level of radiation.

2 more elements

A gas analyzer for detecting at least one component gas in a sample including:

a sample chamber for containing a gas;
a source for producing radiation having at least one absorption line of said at least one component gas, said radiation directed through said sample chamber, and a detector for detecting radiation passing through said sample chamber, said detector producing an output signal that is a particular function of energy applied to said source;
a power supply circuit including a digital-to-analog converter for supplying electrical energy to said source in order to produce a level of radiation that is a function of an analog output of said digital-to-analog converter;
a microprocessor-based control for supplying a digital signal to said digital-to-analog converter for causing said power supply circuit to apply energy to said source at a selectable level in order to produce a selectable level of radiation, said control programmed to supply a digital signal to said digital-to-analog converter that will cause said power supply to energize said source in a manner that will produce a first selected level of radiation with a gas in said sample chamber that is non-absorbing of radiation at said at least one absorption line, and to determine a calibration factor as a function of said output signal obtained thereby;
and
said control programmed to supply a digital signal to said digital-to-analog converter that will cause said power supply circuit to energize said source in a manner that will produce a second level of radiation that is different from said first level, with a sample gas in said sample chamber, and to obtain a sensing value of said output signal;
and
said control programmed to determine a component gas concentration as a function of said sensing value of said output signal and said calibration factor.

5 more elements

Dependencies are inferred from the claim text.