Measuring the pressure dew point tells you whether the dryer is actually achieving the dryness the process needs. The measurement is simple in principle but the sampling point and method determine whether the reading is meaningful.
Where to measure
Sample downstream of the dryer and as close to the point of use as possible. Measuring at the compressor outlet before the dryer gives a wet reading that does not reflect the delivered air. Avoid sampling at low points where condensate collects.
How to measure
Use a dew-point sensor or hygrometer connected at full system pressure, because pressure dew point is pressure dependent. Allow the sensor to stabilise, and record the reading together with the system pressure and flow.
Interpreting the result
Compare the measured dew point with the dryer rating and the ISO 8573-1 water class. A dew point that creeps upward signals dryer overload, a saturated desiccant bed or a failing refrigeration circuit.