GE HumiLab Operator's Manual page 22

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If you wish to perform dew point calibrations in the test chamber,
the display may be reprogrammed to read dew point.
B. CONTROL STATUS Indicator.
you that the control loop that maintains the dew layer on the
chilled mirror is operating correctly, and that there is a proper layer.
When lit, you may consider it to be an indication that the chilled
mirror humidity measurement is valid. Conversely, if the green
indicator is not lit, you should wait until it lights before performing
calibrations.
C. STATUS Window (humidity).
window advises the operator that the sensor mirror has become
contaminated, and requires cleaning.
If you are readjusting the sensor optical balance, a light bar appears
in this window. See "Balancing the sensor optics" on page 37 for
details.
This window will show various indications while reprogramming
the display units or analog outputs. See Appendix B.
D. DISPLAY Switch.
center OPER ate position.
This rocker switch is used to reprogram measurement units and to
check the scale factor of analog outputs.
In the standard configuration, the analog output scale factors can
only be changed using the RS-232 port, to ensure that they are not
changed accidentally. If you wish to reconfigure the system so that
these parameters can be changed via the front panel, see Appendix
B.
E. BALANCE Switch.
AUTO matic position.
AUTO
In the position, the instrument will go through a normal
Pacer® cycle every 12 hours, rebalancing the dew point sensor
bridge and determining whether it requires cleaning.
In the MAN ual center position, there will be no automatic Pacer
cycles, only those initiated manually (if desired).
The green control indicator advises
A green letter "
The DISPLAY Switch is normally used in the
This switch is normally operated in the lower
S " (for Service) in this
Chapter 2 — Operation