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User's Guide _______________________________________________________________________
34____________________________________________________________________ M210543EN-B
The data SRAM test is also done continuously in the background in
normal operation. If a 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 may be fatal (visibility is
indicated using /////). The cause is displayed in the status message.
The EEPROM checksum is calculated and checked during every
update of saved parameters and after restart.
Signal Monitoring
PWD22 measures the optical 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. PWD22 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 data is set to /////.
Offset drift is monitored separately. The reference offset frequency is
given in the configuration session. If the drift is more than 10 Hz, the
software generates a warning.
The user can follow the progress of the measurement sequence as the
Signal/Offset LED sequence of 10 seconds on, and 5 seconds off.
Hardware Monitoring
An eight-channel analog-to-digital converter is used to measure some
signals and various voltages from the hardware. The STA command
displays the internal monitoring values (For details, see Chapter 7,
Troubleshooting, on page 99.
Monitoring Contamination
PWD22 monitors both transmitter and receiver contamination by
measuring the backscattered signal. The CLEAN command is used to
set the clean reference values of the backscatter signals. Deviation of
the backscatter signal from the clean values is proportional to the
contamination on the lenses
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Table of Contents
Troubleshooting
