Vaisala FD12P - Manual (Page 115)

Chapter 5 _______________________________________________________ Functional Description
VAISALA _______________________________________________________________________ 115
During the offset measurement, the yellow LED is off. In normal
operation, the red LED is off.
Memory Tests
After resetting, the FD12P tests and clears its SRAM data memory. It
indicates an error by the red LED blinking. After 50 blinks, the FD12P
tries to start the program anyway. Usually, this causes a watchdog
reset, if the SRAM is really faulty.
The data SRAM test is also done continuously in the background in
normal operation. If an SRAM error is detected, the watchdog resets
the system
The checksum of the parameter memory (EEPROM) is calculated and
checked for test. An error in the checksum is fatal (visibility is output
as /////). The cause is displayed in the status message.
The EEPROM checksum is calculated and checked during every
updating of saved parameters.
Signal Monitoring
The FD12P measures signal, receiver backscatter, and offset as
frequencies in about eight-millisecond samples. As the measuring
times are 10 s, 1 s, and 4 s correspondingly, they must have different
numbers of samples in a batch. The FD12P checks that the frequencies
are not zero and signal sample count is bigger than the offset sample
count.
Errors in signal or offset are fatal and the data is set to /////.
The offset drift is monitored separately. The reference offset
frequency is given in the configuration session. If the drift is more
than 2.5 Hz, the software generates a warning.
Hardware Monitoring
A four-channel, analog-to-digital converter with an eight-channel
multiplexer is used to measure some signals and various voltages from
the hardware. The STA command displays the internal monitoring
values. For more details on troubleshooting, see section Values for
Internal Monitoring on page 137.