Campbell Scientific 0871LH1 Freezing Rain Sensor - Manual (Page 22)

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6 Operator-Initiated Tests
The operator can test the freezing rain sensor functionality by squeezing
the tip of the probe between the index finger and thumb. This simulates
icing by decreasing the frequency of the probe.
With the sensor wired to the datalogger use a digital voltmeter (DVM);
measure DC voltage signal between the Ice signal (blue wire in control
port) and the power reference ground (black wire in G terminal). The
voltage reading should be 4500mvDC to 5000mvDC. When the probe tip
of the ice detector is squeezed; thus changing the frequency and tripping
the probe, the voltage reading will immediately drop to a reading below
500mvDC. Observing this will verify that the probe is operating properly
and give the user enough time to release the probe before it reaches its
full heating temperature.
Once initiated, the heating (de-icing) sequence will quickly heat the probe
to 204.4°C. Though bare fingers must be used for a reliable test result,
there is a danger that you will burn your fingers if you do not let go when
heating has been verified.
7 Initiated Built-In-Test (BIT)
Initiated BIT is performed at initial power-up of the freezing rain sensor
and following power interruptions of not less than 200 ms. Initiated BIT
consists of the following tests:
• The ice and fault status outputs are set in the RS-422 string and on the
discrete outputs so monitoring electronics or test equipment can verify
activation.
• The freezing rain sensor heater is turned on for a short period of time to
verify correct operation of the heater, heater control circuit, and heater
feedback circuit.
• Correct operation of the watchdog timer is verified by simulating a
microcontroller time-out and waiting for a reset input.
• Proper ROM operation is verified by computing a checksum of the ROM
contents and comparing against a a checksum stored in the ROM.
• RAM operation is verified by writing and reading test bytes.
• The Power Interrupt Timer is checked by verifying its transitions to a
“warm” state after performing a “cold” start.
• The power fail input is pulled down to verify a power failure is detected.
• Each time the critical data from the Serial EEPROM is read, a checksum is
read and compared to the checksum computed from the contents. Each
time critical data is written to the Serial EEPROM, a checksum is
computed and stored with the data.
• Resets due to unknown reasons (such as reset from the watchdog timer)
are detected.
Initiated BIT will examine the RESET EEPROM input. If the input is active,
the STATUS output will be set to FAIL and the ICE output and probe
heater will be disabled. (This feature allows a factory technician to
CAUTION: