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
23
of 46
Document title
© 2009-2010; Rotronic AG
23
E-M-HG2-S-V1_04
3.4 Connecting a Chilled Mirror Instrument
Chilled mirror instruments offer the best possible reference measurement thanks to their inherent long
term stability. The use of a chilled mirror instrument (mirror) in partnership with the HygroGen can
reduce the overall uncertainty of measurement by a significant amount (Appendices 1,2 and 3). To
enable the mirror to ‘see’ the HygroGen’s generated humidity, gas needs to be flowed from the
HygroGen chamber through the mirrors measurement cell and (ideally) back. Recirculation limits
thermal and moisture losses from the HygroGen’s chamber, and keeps equilibrium times to a minimum.
Mirrors typically require around 0.5l/min, so non return of the sample will result in worse performance
within the HygroGen chamber and the system overall.
3.5 Sample Loop Operation
HygroGen is equipped as standard with heated sample connection
points on the back panel. The HygroGen sample points and tubing
are automatically controlled to 5 °C above the chamber
temperature to eliminate the possibility of condensation formation.
The connecting tubes to the mirror must also be heated if the set
chamber conditions resolve a dew point temperature higher than
the air temperature through which the sample tubes pass. For
humidity values with a dew point below ambient temperature, heated sample tubes are not required.
Remove the blanking caps fitted to the Swagelok connectors and use connecting nuts and olives to
connect the sample tubes from the chilled mirror. 6 mm OD tubing should be used to connect the
sample loop out and return ports to the chilled mirror unit. The sample loop out port connects to the
HygroGen chamber and is unrestricted. If the mirror instrument does not have a built-in pump, flow
meter and regulator, we recommend including these in the sample loop (after the mirror) to confirm the
air flow rate required by the chilled mirror instrument.
Caution:
•
When tightening or releasing the Swagelok connectors do not apply torque to the
nut/caps without using a spanner on the connector body to counteract it.
•
When not using the sample loop remember to replace the blanking caps.
If the mirror includes the facility for temperature measurement to allow for the calculation of relative
humidity, the probe should be inserted through the chamber door. Care should be taken to ensure that
insertion depth and stem conduction effects do not induce measurement errors. A typical
HygroGen/Chilled Mirror set up is shown below; note the heated sample lines to the rear.
