Due to complexities in dew point measurement, a thermometer is often used for approximate measurement of compressed air's pressure dew point. Despite some error, this method is practical as most condensed water is removed prior to the air-water separator. The best measurement point is at the evaporator's end or separator.
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Answer: The steps of intermittent sampling and measuring the air pressure dew point with a SHAW dew point meter in industrial sites are quite cumbersome, and the test results are often affected by incomplete test conditions. Therefore, in situations where the requirements are not very strict, a thermometer is often used to approximately measure the pressure dew point of compressed air.
The theoretical basis for measuring the pressure dew point of compressed air with a thermometer is: if the compressed air enters the precooler through the air-water separator after forced cooling by the evaporator, and the condensed water carried in it is completely separated in the air-water separator, then the compressed air temperature measured at this time is its pressure dew point. Although the separation efficiency of the air-water separator cannot reach 100% in reality, when the condensed water in the precooler and evaporator is well discharged, the condensed water that enters the air-water separator and needs to be discharged through the air-water separator only accounts for a small part of the total condensed water. Therefore, the error of measuring the pressure dew point using this method is not very large.
When using this method to measure the compressed air pressure dew point, the temperature measurement point should be selected at the end of the cold dryer evaporator or in the air-water separator, because the compressed air temperature is the lowest at this point.
