NDIR gas analyzers frequently work according to the quotient method, where the test channel signal that depends on the concentration is based on a reference channel. Dual channel detectors like the LIM-252 from InfraTec are needed to measure gases. Often, in an optical bench it is necessary to measure two gases at the same time (e.g. CO2 and methane with a reference). Usually two dual-channel detectors, or one dual and one single-channel detector are connected through an external beam divider, because so far pyroelectric detectors with more than 2 spectral channels were only available in a bigger TO8 body (ø 14 mm).
In July 2009 the thermally compensated three-channel detector LIM-253 was introduced as the first component of a new family of very compact multi element detectors in TO39 and TO18 bodies. Like all detectors from InfraTec that are used in measurement applications, Lithium Tantalat (LiTaO3) is used as the pyroelectric element in the LIM-253 too. This guarantees a very low temperature coefficient of the detector signal voltage. The three active and three compensation elements made from 25 µm thick LiTaO3 each have a squared chip area of 1.3 mm. Three built-in JFET impedance converters are connected for the voltage mode. The following standard NBP gas filters for CO2, CH4, CO, HC, and NOX along with the reference filter have been designed in.
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