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

8. Measuring device check (option)8 Measuring device check (option)8.1 Calibration check procedureIn the course of various studies and experience of practical use, the"adjustment by stochiometric reduction" method has established itself. Thismethod leads to stable adjustment points on the one hand, but on the otherhand is only reproducible if fresh SnCl 2 solution is applied immediately beforethe adjustment run. This behaviour is due to the oxidation and light sensitivityof the aqeous Sn² + solution.In practice, an Sn²+ concentration of 10 g/l has proved to be sufficient for anadjustment time of 90 minutes.With this configuration, adjustment points of up to 2 mg/Nm³ Hg can beachieved with linear dependency for volumetric flow rates of 80 - 120 l/h.8.2 Factors influencing the calibration pointThe calibration point is essentially dependent on the following parameters:• Dosing capacity of the hose pump (Hg²+ solution)• Volume flow of the measuring gas• Concentration of the Hg²+ dosing solution• System pressure• Temperature of the measuring gasThe dosing capacity of the hose pump can be simply determined through"volumetric measurement" or weighing a volume of fluid pumped in the timeunit. This process is generally only necessary once. However, fluctuations canoccur in the flow rate after prolonged operating times due to material fatigue inthe hose systems.The volume flow of the measuring gas can affect the quality of thecalibration point in the range > 100 l/h. This effect is particularly evident in thecase of calibration above 300 µg/Nm³. For this reason, volume flows ≥ 100 l/hare generally desirable. Volume flows above 150 l/h cause erratic lowering ofthe system pressure and over-intensive purging of the Sn² + receiver, whichimpedes uniform gas discharge (Hg) (frothing of the calibration solution).The concentration of the Hg² + dosing solution has a direct influence on thecalibration point, in accordance with the formula specified below.The system pressure and the temperature of the measuring gas areessential parameters for converting the concentration from µg/m³ to µg/Nm³.The temperature is determined with a PT100 at the measuring cuvette of thephotometer (gas inlet) and displayed in calibration mode. The system pressureis a direct measurement for the volume flow and tightness of the system. Thetightness should basically be inspected before each calibration by checkingthe gas quantity at the gas inlet of the measuring device in comparison withthe gas quantity at the gas outlet with a gas meter. The system pressure istherefore an instrumental parameter dependent on volume flow, barometricpressure and transport cross-sections, which is displayed in calibration mode.HM 1400 TRX 69