Sampling is needed when direct measurement of the air or gas is not possible or desirable. This may be related to, for example, a high process temperature, protecting the sensor from water spikes, the need to easily detach the instrument from a pressurized process without running the whole process down, or wanting to make the measurement at a more convenient location.
Keep in mind that changing the pressure of a gas changes the dew point temperature of the gas. If the sensor is at a different pressure than the process itself, there may be an error of several tens of degrees in the dew point measurement.
Make sure there is sufficient flow of gas to the sensor (for example, 1 l/min) to give a representative sample.
|You can use the Vaisala Humidity Calculator to simulate the effect of pressure change to dew point. The Humidity Calculator is available at: www.vaisala.com/humiditycalculator.|