Campbell Scientific 0871LH1 Freezing Rain Sensor - Manual (Page 21)

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• The MSO is operating correctly. Frequencies between 39000 and
40150 Hz are valid.
• The probe heater is de-icing correctly. After turn-on, the probe heater
must cause the MSO frequency to return to at least 39970 Hz within
the 25 second timeout or it is considered failed.
• Probe is de-iced within 25 seconds. (De-Icing Fail).
5 BIT Failure That Disables Ice Output
The Ice output is disabled due to Continuous and Initiated BIT failures as
shown in Table 1 - BIT Information. Ice detection is disabled when these
failures occur because the integrity of the ice detection capability has
been compromised.
Table 7. BIT Information
Title
Disable Ice
Detection 1
Initiated BIT
Continuous
BIT
MSO Fail, High X X
MSO Fail, Low X X
EEPROM Fail X
RAM Fail X X
ROM Fail X X
Watchdog Fail X
Power Interrupt Timer Fail X
Power Fault Monitor Fail X
Probe Heater Always ON or OPEN Active Test Passive Test
Probe Heater Always OFF Active Test Passive Test 2
Probe Heater ON w/ 1 Enable X
De-Icing Fail Clear Only Set Only
Unknown Reset Failure X
When the failure is enunciated, the software no longer provides
ice detection capability.
In Continuous BIT, the “Probe Heater Always OFF” failure is set
when the heater is ON and a de-icing failure has been detected. If
the frequency indicates that the ice has been removed within the
expected time, the software will not annunciate the probe heater
failure. The actual failure is most likely due to a problem in the
heater feedback circuitry rather than heater control circuitry. The
failure will be enunciated the next time IBIT is performed.
NOTE:
NOTE: