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
31
of 46
Document title
© 2009-2010; Rotronic AG
31
E-M-HG2-S-V1_04
6.3 External RH Probe Reference
An external RH reference is applied through the HygroGen door in the same way as an instrument under
test. This method involves the user comparing the measurement values from the reference instrument
being compared to the instrument under test
Advantages:
•
Users may already have an existing reference instrument within their Quality system, so being
able to make use of this can be cost effective.
•
Once established, traceability between the HygroGen and external reference instrument used
means that the HygroGen can remain in use whilst the reference calibration is performed.
Disadvantages:
•
RH probes of all types can drift over time, so regular reference calibration checks need to be
performed to achieve best performance or a drift component must be included in an overall
uncertainty calculation.
•
Connecting the reference ‘through the door’ means that energy may be gained or lost through
the probe shaft at temperatures above or below the ambient temperature where the HygroGen
is used. A supplementary uncertainty component is therefore required.
•
Probe characteristics such as hysteresis or temperature coefficients must be included within the
overall uncertainty budget.
•
After use at high RH conditions, absorption/adsorption effects may increase repeatability values
•
To achieve the lowest possible uncertainty, reference characteristics may need to be
determined within calibration
If the use of an external reference is your preferred option, our recommendation would be to refer to
the instrument manufacturer or an accredited calibration laboratory for guidance on how to achieve the
best possible performance.
As with the internal reference option, interim calibration checks against a traceable standard will
minimise risk, improve confidence and help justify improved drift uncertainty components.
