Appendix B — Humilab chilled mirror hygrometer details Page 59
Troubleshooting
the chilled
mirror
hygrometer
system
The following factory test procedures can be performed for
incoming inspection or for troubleshooting purposes. They should
only be done by a trained electronics technician.
Front panel does not light when powered up.
• Check the POWER switch. Make sure it’s ON.
• Check the line cord. Make sure it is plugged into a proper
source of AC voltage.
• Check the power supply. Make sure it is connected and has
the proper output voltage.
• Check the fuse. Make sure the proper fuse size is installed.
Make sure the fuse is not open.
“S” appears on the front panel display.
The “S” means service is required. The usual problem is that the
sensor mirror is contaminated and should be cleaned.
• Clean the sensor mirror as described in Chapter 5.
• Run the instrument through a Pacer cycle.
• If, at the end of the cycle, the “S” comes on again, balance the
sensor optics as described in Chapter 5.
Invalid dew point display.
This can be caused by one of three problems.
• Clean the mirror as described in Chapter 5.
• Balance the sensor optics as described in Chapter 5.
• If the above procedures have been done and the problem per-
sists, verify that the platinum resistance thermometer in the
sensor is reading correctly:
1. Disconnect the 6-pin connector (J9) from the main circuit
board in the Electronics Module. Once disconnected, the front
panel dew point display should read ambient temperature
after allowing sufficient time for the sensor mirror to stabilize
at the new temperature.
2. Check the temperature reading against another reliable ther-
mometer placed near the dew point sensor. Allow sufficient
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