LASER COMPONENTS has introduced five new bandpass filters for pyroelectric detectors, increasing the number of standard filters available to an outstanding seventeen versions. The new filters include reference filters (B) and filters for the detection of CO2 (A), water vapour (M), methane (S), and alcohol (O), and are either mounted directly inside the fixed cap of the detector or available as a separate cap, which is then mounted to an existing pyroelectric detector.
A reference filter should not have any gas absorption. Filter B can be used when SO2 is part of the gas mixture (peak = 3.86μm, FWHM = 90 nm). The CO2 filter A with a peak = 4.265μm is the filter with the best possible signal and simple linearisation (FWHM = 110nm).
Water vapour is in almost every gas mixture, which often leads to a disturbing background noise. An attempt to measure this with a 2.94μm filter, for example, leads to problems of cross-sensitivity with CO2. The M filter has proven more reliable in such practical applications: peak = 5.78μm, FWHM = 180nm.
Methane is primarily measured at 3.33μm; however, this is not particularly specific. An excellent alternative is the S filter, which operates at a longer-wave band: peak = 7.91μm, FWHM = 160nm. Breath alcohol measurement is becoming more and more popular. The new standard filter has the following specifications: peak = 9.50μm, FWHM = 450nm.