ROTRONIC Hygrogen2 - Manual (Page 60)

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 56 of 75
Document title
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 and documented.
A1.2 External RH Probe Reference
Any RH instrument placed through the HygroGen2 door can be used as the reference. This may be
desired if your quality system employs a particular RH probe with a long history. It may not be
desirable to adjust this probe and use it as the control probe – a separate adjusted control probe may
be more convenient.
The same disadvantages apply when using an external RH probe as a reference as when using the RH
control probe: i.e. accuracy, susceptibility to drift, hysteresis, regular calibration requirement.
A1.3 Chilled Mirror Reference
To reduce calibration uncertainty, a chilled mirror instrument can be employed as the reference. This
type of instrument is generally accepted as a secondary humidity transfer standard. Instruments
should be maintained with an accredited (ISO 17025) calibration certificate. A chilled mirror can be
used to validate the HygroGen2 calibration before and after on-site calibration using the internal RH
probe as a reference.
Chilled mirrors measure “dew point“, which is a measure of water vapour concentration and is the
temperature at which dew will form on a surface. Relative humidity can be derived from this value
with a corresponding temperature measurement.
There are two types: an all-in-one probe which can be inserted through the HygroGen2 door, with
integrated PRT temperature probe, e.g. MBW/RHS 473 with RP2 measuring head, and an external
sampling head, for which the HygroGen2 external sample loop is employed (see section below).
Advantages of chilled mirror references:
• Best measurement capability.
• Instruments do not drift significantly.
• Operates over a broad range of humidity conditions.
© 2014; Rotronic AG E-M-HG2-S-V2.1