Trace moisture sensors must be tested for suitability, accuracy, and reliability. In cooperation with BAM/Berlin a measurement station was developed, constructed and installed for the testing and approval of trace humidity sensors. A mixing gas generator generates a dew points of-70 °C. Several dew point sensors can be connected at the same time to the measurement station for testing. A dew point mirror is connected as a reference hygrometer. The setting of different moisture values as well as the recording of the measured data is carried out automatically.