SIMRAD GD10P - IR GAS DETECTOR - ICEWeb

22Refer to Figure 5.2 below.Radiation from two infrared sources passes through two narrowbandfilters selecting a measuring wavelength and a reference wavelength.The sources are electronically chopped. Radiation is divided by abeamsplitter into an internal and external path. The internal path isviewed by the compensation detector, and the external path is viewedby the measuring (main) detector. The compensation detectormonitors and compensates for drift in sources or detectors. The maindetector monitors the external measuring path and detects whether theselected gas is present.The four signals, two from the compensation detector and two from themain detector, are amplified, digitised and fed to the microprocessor.The signals are used by the microprocessor to calculate the gasconcentration. The gas response is then linearized and presented aseither a voltage, a current or a digital output signal. Internal signals arecompared with test limits to monitor electronics and optical parts. Ifvalues outside the test limits are found, specific error messages aregiven.Optical filter characteristics remain constant over time, and drift in theother components is monitored and compensated by the dualwavelength, dual path concept. This means that the zero and gas spanfactory calibration will remain stable regardless of component drift, andthat the detector needs no manual recalibration after factorycalibration.