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HygroGen Calibration Traceability

Calibration of ROTRONIC probes: using the HygroGen, a 2-point temperature adjustment of the ROTRONIC humidity-temperature probes should be done at 20°C and 45°C. Humidity adjustments should be carried out at 35, 80 and 5 or 10%RH, all at 20°C. Obviously, the HygroGen can also be used to calibrate non-ROTRONIC humidity instrumentation.

Humidity and temperature reference: Preferably, the temperature reference should be provided by a certified precision PRT inserted through the chamber at the same immersion depth as the probes to be calibrated. As an alternative, an SCS certified HygroClip S may be plugged into one of the two spare MOC connectors inside the chamber. We do not recommend using the control Pt100 RTD as the temperature reference. Depending on the model of HygroGen, the following alternatives are available regarding the humidity reference: HygroGen 1: use a set of SCS certified HygroClip probes, inserted one at a time through the chamber door at the same depth as the probes to be calibrated. To avoid sensor hysteresis and loss of accuracy, each probe of the reference set should be used exclusively at a defined humidity value (example: 10, 35 and 80%RH for 3 probes). When not in use, the probes should always be stored in a dry environment. We do not recommend using the control HygroClip S as the humidity reference. HygroGen2: use a certified condensation hygrometer connected to the HygroGen (this model has an internal air pump to circulate air through an external sampling loop). Limitations of humidity sensors based on a polymer: When the humidity reference is provided by a probe with a polymer sensor, the user should beware of so-called sensor hysteresis. Sensor hysteresis occurs when a polymer sensor is exposed to humidity above 50 to 60 %RH and results in a temporary positive calibration shift when the sensor is returned to lower humidity. The magnitude of the calibration shift depends on the maximum humidity to which the probe was exposed, on the duration of the exposure and on the make of sensor..