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

4. Theoretical foundationsdisplay value of 0 µg/Nm³ will appear on the display when the potentiometer isin the central position. A shift of this symmetry towards positive values will notadversely affect the linearity of the measuring range. If the optics are so soiledby impurities that a display value of 300 µg/Nm³ or higher results at the lefthandstop of the potentiometer, then the photometer optics must be cleaned.Contact the Service department to clean the photometer.Information is available from the Verewa Service department.Information on the offices or partners responsible can be found on the Internetat all times, see manufacturer address on Page 2, or DURAG GROUPcompany addresses see page 107.4.5 Volume control and system pressure measurementThe measuring device is equipped with a measuring gas pump (type:membrane pump). This vacuum pump sucks up the measuring gas at thesampling point and pumps it through the complete measuring device. Themeasuring gas only flows through the volume control and the pump itself afterit has been measured in the photometer.The Figure 4.4: Volume control and system pressure measurement shows thegas flow measurement (differential pressure transducer, differential pressurenozzle), the gas volume presetting and the measuring components forstandardisation (absolute pressure transducer, gas temperaturemeasurement), which are arranged on an installation panel on the back of themeasuring device. These components are maintenance-free, from theannual replacement of the pump's wearing parts.The control valve enables correction of the sampling gas flow. As guide value,a volume flow of 90 to 100 l/h should be set. The measuring device operatesas a concentration measuring device and is therefore independent of the flow.However, an inadequate flow will cause an unnecessary extension of the T 90time, while an excessive flow will result in an inadequate system pressure,which will then be incorporated into the standardisation calculation as acorrespondingly high mathematical proportion. The volume flow is measuredwith a differential pressure nozzle operated on the pressure side.System pressuremeasurement500...1200mbarVolume settingDifferential pressuremeasurement venturi flowcontroller 0 ...15 mbarMeasuring gas pump,V max.: 400l/hFigure 4.4: Volume control and system pressure measurement36 HM 1400 TRX