HM 1400 TRX Total Mercury Analyser - Webshop, Gas Analysis ...

4. Theoretical foundationss these electrons fall back to the original basic state "in a step-by-step fashion"via several intermediate energy stages. The light released during this processis emitted undirected into space. The measured weakening in intensity is thenproportional to the mercury concentration, based on the Lambert-Beer law.slitdiaphragmreference cuvettelampiodinecharcoalfilterdhg1400tr_04_001measuring cuvettephotodiodesFigure 4.3: Schematic drawing of the gas flow through the Hg photometerThe arrows symbolise the gas flow through the photometer. The measuringgas enters the measuring cuvette, is then conveyed through a selective filterfor mercury, where it is adsorbed and then flows through the referencecuvette. The advantage of this cuvette circuit is that the entire gas matrix flowsthrough both the measuring cuvette and the reference cuvette, and themercury is filtered out largely selectively before the reference cuvette. Thisdifferential measurement principle means that, in comparison with the singlebeamphotometer, which only has one cuvette, the measurement is at least 10times less susceptible to spectrometric interfering components. For example,in the case of a single-beam photometer, from 50 mg/m³ SO 2, SO 2 is alsomeasured instead of Hg. A higher value, which does not actually exist, isultimately simulated for the mercury concentration. In extreme cases, arandom measuring value can be displayed for Hg due to SO 2 , although nomercury is actually present.In the cuvette circuit of the two-beam device, this cross-sensitivity only takeseffect from 500 mg/m³ SO 2 . From 500 mg/m³ SO 2 scrubbers are available,which eliminate the SO 2 . Reliable measurement is thus also guaranteed withSO 2 concentrations from 1.5 to 2 g/Nm³.The measuring signal from the photometer and the measuring signals from thepressure and temperature measurement after gas drying are sent to theinternal PLC. The mercury concentration is now calculated and the measuringresult is output in µg/Nm 3 (dry).4.4 Cleaning the photometerThe photometer is set to a measuring range of 0...500µg/m³ → 0...10 V outputvoltage. According to the basic setting, the display range is programmed to0...45 µg/Nm³ → 4... 20 mA output signal of the HM 1400 TRX. The remainingapprox. 455µg/m³ (measuring range reserve of the photometer) are madeavailable for the zero offset. On the side of the photometer there is apotentiometer, on which the zero offset can be adjusted. It must be ensuredthat a positive value is shown on the display of the HM 1400 TRX (basicsetting approx. 20...30 µg/Nm³). If the photometer is absolutely clean, then aHM 1400 TRX 35