Vaisala LT31 - Figure 27 PWD Forward Scatter Sensor; Present Weather Detector Forward Scatter Sensor

Chapter 3 ______________________________________________________ Functional Description
VAISALA _______________________________________________________________________ 59
- Configurable host interface
- RS-232 with RTS/CTS
- RS-485
- Socket for optional modem
- Power supply
The master CPU software can be updated using the maintenance or the
host interface.
Present Weather Detector Forward
Scatter Sensor
A Present Weather Detector (PWD) forward scatter sensor (see Figure 27
below) is mounted to the support arm of the LT31 transmitter unit. It is
used for auto-calibration and for present weather detection (optional).
0401-043
Figure 27 PWD Forward Scatter Sensor
The key functions of the PWD forward scatter sensor include the
following:
- Accurate measurement of the prevailing visibility based on proven
forward scatter principle
- Scientifically valid chain of calibration
- Extensive set of self-diagnostics and automatic detection of
contamination ensures that false values are not reported
- Easy calibration
- Weather-proof mechanical design
The PWD forward scatter sensor is connected to the power supply and to
the module bus terminals (RS-485) of the interface unit of the LT31
transmitter.