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XDT Manual - Pioneer Air Systems Engineering

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Section 2: Sensor and Sampling Techniques2.3.1 In-situ InstallationIn-situ installation is recommended only for measurements where the gas pressure is expected tovary little, the gas is expected to be free of contaminants, the gas temperature is within the operatingspecifications of the sensor, and there is no chance of liquids coalescing. Examples of applicationssuited for in-situ installations are: pure gases, output of desiccant dryers (for instrument air),glove boxes, etc. For most other applications in-situ installation should be avoided for the followingreasons:• Sample conditioning is almost always necessary to avoid exposure of the sensor to liquidwater and other contaminants, such as hydrocarbons, which may damage the sensor or affectaccuracy over time.• Variations in line pressure affect the reading of the sensor because dewpoint varies with pressure.• If the gas line is under pressure, it is more likely that water condensation occurs which maydamage the sensor.• Under a pressurized system removal of the sensor without the installation of isolation valvescan be dangerous.If in-situ installation is required, bypass mounting is preferable; make sure to install the sensor atthe upper surface of the gas line to minimize its exposure to liquid water, should condensationoccur, the XTR65W sensor is best suited for these applications. Also consider the need to isolate(depressurize) before installing or removing the sensor.MainGas LineIn-Line Installation, SensorMeasuring at Line PressureNOT RECOMMENDEDSafety shut-off ValveBypass Installation, SensorMeasuring at Line PressureSample CellSafety shut-off ValveMainGas LineBypassControlValve ** maintain differential pressure to provide adequate flow through sample cellThe sensor measures the dewpoint at whatever pressure it is at. The instrument is equipped with apressure correction feature which allows reporting the dewpoint at a different pressure.5

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