E-M-HG2-S-V1_04
Rotronic AG
Bassersdorf, Switzerland
Document code
Unit
HygroGen2 humidity and temperature
generator: Instruction Manual
Instruction Manual
Document Type
Page
29
of 46
Document title
© 2009-2010; Rotronic AG
29
E-M-HG2-S-V1_04
Section 6: Calibration Reference Options and Uncertainty
The calibration of humidity and temperature with any system requires careful consideration to achieve
best possible results. The HygroGen provides users with a convenient tool to achieve precise results with
even limited previous experience or expertise.
The ‘precision’ of a humidity calibration is correctly described and defined in terms of its ‘uncertainty’.
The Guide to Uncertainty of Measurements (GUM) and
ISO/IEC 17025:2005 “
General Requirements for the
Competence of Testing and Calibration Laboratories”
are the internationally recognised standards users
should refer to in this respect. The following Sections and the uncertainty budgets included are for
guidance only, and ROTRONIC accepts no liability whatsoever in relation to their use.
Almost certainly, your need to calibrate is based on the need to meet the requirement of traceable
calibration within a quality system. In which case, consideration of the uncertainty of measurement will
either be a necessity, or soon will be. Appendices 1…3 provide examples of uncertainty budgets for the
HygroGen when using different calibration references. These will enable you to support any claim of
traceability or calibration uncertainty.
If your need for improved calibration is a desire to improve the precision or repeatability of your
measurements to improve processes or optimise control efficiency, then the framework the uncertainty
brings may provide a useful tool to help identify where improvements can be gained.
The uncertainty components listed are based on those already in use. Should you become aware of any
possible additions, or require support, please contact ROTRONIC or your local supplier.
6.1 Humidity Calibration Reference Options.
There are three main methods of establishing the calibration reference with the HygroGen. Each has its
own advantages and disadvantages, so the method chosen should be on the basis of the needs of the
application, practical issues and the uncertainty required. Each should be considered with reference to
the uncertainty budgets detailed in the appendices.
The options are:
1)
Internal control RH probe reference
2)
External RH probe reference
3)
Chilled Mirror Hygrometer reference
In each case, the primary concern must be the comparison of the temperatures measured by the
reference, the HygroGen, and instruments under test. RH is significantly temperature dependent, so you
can almost forget accurate RH measurement if the temperature measurement is not optimised.
