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.
Caution: 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.
15