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
30
of 46
Document title
© 2009-2010; Rotronic AG
30
E-M-HG2-S-V1_04
6.2 Internal RH Probe Reference
HygroGen uses a ROTRONIC HygroClip RH and temperature probe for control. The HygroClip provides a
digital signal to the HygroGen control system, so there can be no degradation of the measured value
due to (for example) analogue to digital conversion. HygroGen’s displayed measurement values can
therefore be used as the reference:
Advantages:
•
No supplementary instruments are required, so use ‘on site’ is more convenient.
•
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 readily replaced with another calibrated probe*.
•
HygroClip probes have the facility to be adjusted exactly to agree with a calibration reference,
meaning no corrections of the HygroGen 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 drift component must be included in an overall uncertainty
calculation.
•
Probe characteristics such as hysteresis or temperature coefficients must be included within the
overall uncertainty budget
Using the internal probe as your reference provides the most convenient option, but without routine
checks of the probe’s stability, there is risk that probe damage or drift could undermine the quality of
your calibration work. Interim calibration checks against a traceable reference (e.g. ROTRONIC SCS RH
standards) should be carried out periodically and the results recorded in a probe calibration history.
Annual recalibration of the control probe by an accredited laboratory should be the minimum
calibration regime. Interim calibration checks in combination with the annual calibration results will
allow the key drift component of an uncertainty budget to be defined with documentary support.
* HygroGen’s with serial numbers 001-060 may require the control/reference probe to be matched with
the HygroGen digital electronics to ensure compatibility (baud rate synchronisation). It is recommended
that the spare HC2-S probe is pre-purchased in good time and checked in the HygroGen before
calibration takes place. Spare probes can be supplied during the annual service to support this.
HygroGen serial number 061 onwards incorporate a scanning function to guarantee compatibility with
any HygroClip probe.
