TABLE OF CONTENTS Keyword Infrared
A new direct modulated infrared source for infrared (IR) gas analysers is now available from Heraeus Noblelight, of Bromborough, UK. The new source utilises carbon fibre element technology to eliminate the need for mechanical modulation and employs gold reflectors to direct the IR beam (see Plate 1).
IR gas analysers often use a thermal source of IR, which is modulated by means of a rotating mechanical chopper. For most applications in process gas analysis, this modulation is in the frequency range 2-6Hz and is important in ensuring a clean signal with the minimum of noise. However, to achieve the degree of modulation necessary, mechanical choppers must be very precisely manufactured and are consequently very costly.
The new IR source features carbon fibre heated ribbons, which offer relatively high emission coefficients (around 0.85) together with a low thermal capacity. As a result it is now possible to modulate the source electronically in the output range 5-10Watts, so eliminating the need for a mechanical chopper. The source can be used in the standard wavelength range (3-5 m) of automotive exhaust gas and process gas analysers, with modulation frequencies in the range 2-6Hz. A modulation depth can be achieved similar to that available with mechanical choppers.
The new source can also be used in out-of-phase modulation in double beam analysers. Unlike conventional sources using beam choppers, where compensation to adjust the sample and reference beam synxnetry is achieved by means...
