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USER'S GUIDE____________________________________________________________________
Additional Measurements
22 __________________________________________________________________ M210543EN-E
An extra photodiode measures the light scattered backwards from the
lens, other objects or contaminants. This signal is also monitored by the
CPU.
Light Receiver
The Light Receiver consists of a PIN photodiode, preamplifier, voltage to
frequency converter, backscatter measurement light source LED, and
some control and timing electronics.
The receiving PIN photodiode senses the transmitted light pulses
scattered from the aerosol particles. The signal voltage is filtered and
detected by a phase sensitive lock-in amplifier synchronized with the
transmitter.
An ambient light level as high as 30 kcd/m
detection of the photo diode, neither does it saturate the preamplifier. The
AMBL signal (proportional to the ambient light) is lead to the CPU for
monitoring.
PWD22/52 includes RAINCAP
precipitation, and the TS Temperature Sensor for measuring the sensor
cross arm temperature (TS). Both additional sensors are measured and
interfaced by the PWC22/52 board. The RAINCAP
is measured for the RAINCAP
(PWC22/52) temperature TB is measured for the box heating monitoring.
Vaisala RAINCAP
®
The RAINCAP
signal is proportional to the water amount on the
sensing surfaces. Water on RAINCAP
sensor elements. The capacitance of the elements controls the output
frequency of an oscillator.
The frequency signal is measured once a second. The frequency is
handled in the PWD22/52 internal units. The DRY value is about 800,
which is also shown in the Status (STA) message.
2
does not influence the
®
for estimating the water content of
®
heating (drying) control, and the box
®
Rain Sensor
®
changes the capacitance of the
®
temperature TDRD
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Troubleshooting
