Monitoring Contamination - Vaisala PWD22/52 User Manual

USER'S GUIDE____________________________________________________________________
28 __________________________________________________________________ M210543EN-E

Monitoring Contamination

PWD22/52 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
The alarm and warning limits are given in the configuration session. If
the alarm limit is exceeded, data is set to ///// and an alarm is generated.
The measured values are used only for warnings and alarms. No
compensation for the visibility signal is calculated.
Transmitter backscatter is measured by an analog circuit using the
transmitter LED as a light source. Its identifier is TR.BACKSCATTER
in the status message. TR.BACKSCATTER is smaller for higher
backscatter signals. Receiver backscatter is measured with the signal
receiver using an additional, controlled LED as a transmitter. The result
is in hertz. It is bigger, when more light is scattered back (REC.
BACKSCATTER).