ROTRONIC Hygrogen2 - Manual (Page 59)

E-M-HG2-S-V2.1
Rotronic AG
Bassersdorf, Switzerland
Document code Unit
HygroGen2 Humidity and Temperature Generator:
Instruction Manual
Appendix
Instruction Manual for Software
Version 2.1
Document Type
Page 55 of 75
Document title
A1: Calibration Reference Options
Various calibration references can be used with the HygroGen2. These include the internal control
probe, other RH probes, dew point chilled mirrors and platinum resistance thermometers (PRTs).
For traceable calibration, these references are themselves calibrated by accredited laboratories
traceable to national standards.
For more information, please refer to The Guide to Uncertainty of Measurements (GUM) published
by the UK National Physical Laboratory (or equivalent national standards documentation) and ISO/IEC
17025:2005 “General Requirements for the Competence of Testing and Calibration Laboratories”.
Appendix D1 provides examples of uncertainty budgets for the HygroGen2 when using different
calibration references. These are for guidance only and ROTRONIC accepts no liability in relation to
their use.
A1.1 Internal RH Probe Reference
The display values on the HygroGen2 (which are derived from the control probe - as described in
Appendix A2 ) can be used as the reference.
Advantages:
• No supplementary instruments are required.
• Fastest response - control is based on the reference value.
• Stability during calibration – the reference is continually optimising the control value.
• The reference probe can be easily replaced with another calibrated probe.
• HygroClip probes have the facility to be adjusted to agree with a calibration reference,
meaning no corrections of the HygroGen2 display value need to be made in routine use.
Disadvantages:
• RH probes can drift over time, so regular checks need to be performed to achieve best
measurement capability and a larger drift component included in an overall uncertainty
calculation.
• Probe characteristics, such as hysteresis or temperature coefficients, must be included within
the overall uncertainty budget.
• RH probes are less accurate than chilled mirrors.
Using the internal probe as your reference provides the most convenient option, but routine checks
of the probe’s stability are required to ensure the quality of the calibration. Interim calibration checks
against a traceable reference (e.g. ROTRONIC non-saturated salt solutions) should be carried out
regularly and the results recorded in a probe calibration history.
© 2014; Rotronic AG E-M-HG2-S-V2.1