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Feuchtegenerator Thermodynamisches Labor

Highest metrological know-how

Primary standard humidity


Primary standard humidity

The primary humidity generator extends the thermodynamic laboratory by a high-precision measuring facility for the calibration of dew point hygrometers and humidity sensors

Testo Industrial Services is the expert for thermodynamic measuring devices for climate measurements. Besides capacitive and resistive humidity devices/data logger/transmitter, high-precision reference standards such as dew point mirrors and dew point transmitters can also be calibrated in our accredited laboratory

With the extension of a new primary humidity generator, the thermodynamics laboratory of Testo Industrial Services is completed by a further measuring system. Thus, in addition to calibrations in the various climate chambers, such as the Thunder or Huminator, precise calibrations of humidity measuring devices can be offered. The new primary standard enables the fully automated display of stable and reproducible humidity values in a wide measuring range from 5 to 95% RH (-25 to 95°C frost/dew point) with the smallest measurement uncertainties in Europe. The primary standard is based on the 2-pressure-2-temperature principle, which generates a continuous humid air flow with defined and constant climatic conditions. In the high pressure range (saturator), humid air is completely saturated at a specified temperature up to a pressure of 10 bar and in the low pressure range (calibration chamber) it is expanded to atmospheric pressure.

In the process, the humidity drops because the water molecules are distributed over a larger volume. The absolute humidity of the generated air flow can be determined by the quotient of calibration chamber pressure and saturator pressure as well as the saturator temperature. For the determination of the relative humidity the measured calibration chamber temperature is also required. Thus any temperature and humidity point can be generated. During the calibration, the measured data of the test equipment are compared with the calculated reference values of the primary humidity generator. 

In addition to the Physikalisch-Technische Bundesanstalt (PTB), the procedure is also used by other national metrological institutes for the primary representation of the measurand humidity. 

Amongst others, the following test equipment can be calibrated in the primary humidity generator:

  • Dew point mirror
  • Dew point measuring devices
  • Data logger
  • Transmitter
  • Electrical hygrometers
  • Humidity / temperature measuring devices
  • Humidity probes
  • Humidity sensors
 primary humidity generator

Due to the large measuring range and low measurement uncertainties, the humidity generator is used for the calibration of dew point mirrors as reference standards of accredited and non-accredited calibration laboratories and for the calibration of precise reference hygrometers (dew point meters, capacitive/resistive hygrometers) in the industrial, pharmaceutical and food areas. Furthermore, dew point mirrors can be calibrated for the validation of climate cabinets and climate chambers.

The technical data at a glance:

  • Temperature range: 0°C ... +95 °C (measurement uncertainty 0.2 K)
  • Humidity range: 5 ... 95 %RH (measurement uncertainty from 0.2%rh)
  • Frost/dew point temperature: -25°C to 95°C (measurement uncertainty from 35 mK)

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