New Transfer Standard Hygrometer for Environmental Test Applications

MBW Calibration is a Swiss manufacturer of transfer standard chilled mirror dew point hygrometers used at most National Metrology or Designated Institutes. The precision and stability of dew point mirrors is such that they are used as transfer standards in many humidity/moisture measurement applications and for traceable calibration.

With the introduction of the new 473-SHX high temperature dew point mirror, measurement precision at high operational temperatures reaches a new level of performance in industrial applications such as climatic test chamber calibration or validation.

Dew point mirror hygrometers measure on the basis of thermodynamic equilibrium between the sample gas and the condensation layer. Instability of sample pressure and flow results in non-stable measurements, especially at high temperatures and when the output value is relative humidity (RH).

For dew point measuring heads placed directly in to test chambers, the challenge to our development team was to provide stable flow whilst meeting an operational temperature requirement of 125°C. The solution is a completely new design sample gas flow module based around a high temperature micro motor and a custom turbo impeller that fits directly to the SHX measuring head.

The cable mounted SHX measuring head is also available with a temperature control option that enables the test engineer to set the head temperature to avoid condensation during transitions or stabilise gradient effects in small test chambers. The result is a dew point mirror that can measure precisely over a wide operating range with consistent measurement precision and no temperature coefficient.

This new instrument brings laboratory precision to a wider range of industrial, calibration and test applications. In combination with the MBW T12 multichannel thermometer and GeckoR2 software, RH and temperature homogeneity evaluation can also be performed. With all measurement parameters calibrated to an ISO17025 standard, traceable, low uncertainty calibration is now possible over the range -50 to +125 °C and humidity up to 100 %rh.