Dräger 4543445, Operating Manual

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5.3 Operating Principle for DraegerSensor IR
The DrägerSensor IR infrared gas sensor is a gas transmitter designed to
determine the concentration of gases and vapors in the ambient air. The
principle of measurement is based on the concentration-dependent absorption
of infrared radiation in measured gases.
The monitored ambient air diffuses through sintered material into the
flameproof housing of a measuring cuvette. The broad-band light emitted by the
radiator passes through the gas in the cuvette and is reflected by the cuvette
walls from where it is directed towards the inlet window of a dual element
detector. One channel of the detector measures the gas-dependent light
transmission of the cuvette (measuring channel), the other channel is used as
reference. The ratio between measuring and reference signal is used to
determine the gas concentration in the cuvette. The cuvette is heated to avoid
condensation of the atmosphere’s moisture content.
Internal electronics and software are used to calculate the concentration. As an
output signal, the gas sensor emulates the half bridge of a catalytic Ex sensor.
Die to its robust design and the measuring method the gas sensor has long
maintenance and calibration intervals (see manual 9023843, Maintenance).
A gas sensitivity drift is practically excluded by the infrared-optical principle of
measurement and in addition, the zero point stability is enhanced by an
automatic tracking system.
Operating Principle for DraegerSensor IR