Vaisala PWD22 User Manual page 77

Chapter 5__________________________________________________________________ Operation
VAISALA ________________________________________________________________________ 75
usually used to drive external relays. For details on relay logic
description, see section Relay Controls on page 50.
Backscatter/contamination control is done by comparing the current
values of backscatter signal with the reference values given with the
CLEAN command. The limits given here are limits for the change in
backscatter signals.
TRANSMITTER CONTAMINATION LIMITS
WARNING LIMIT ( 1.0) 1.5
WARNING LIMIT UPDATED
ALARM LIMIT ( 5.0)
The transmitter values are in volts (V). The measurement range is 0 ...
13 V, where 0 V is a blocked lens. The limit value is given as a
positive value although the signal becomes smaller when
contamination increases. A contamination change of 5 V represents
about a 10 % decrease in the transmitter's lens transmittance (and also
a 10 % increase in visibility indication).
RECEIVER CONTAMINATION LIMITS
WARNING LIMIT (
ALARM LIMIT ( 500) 600
ALARM LIMIT UPDATED
The receiver values are expressed in hertz (Hz). The measurement
range is 0 ... 10 000 Hz, where 10000 Hz is a blocked lens.
A contamination change of 500 Hz represents about a 10 % decrease
in the receiver's lens transmittance.
The system response to the CONF command is presented below.
ANALOG OUTPUT MODE
Default 0, linear visibility to current mode.
ANALOG VISIBILITY MAX
Default 2000m.
MAX VISIBILITY CURRENT
Default 20 mA.
ANALOG VISIBILITY MIN
Default 10m.
MIN VISIBILITY CURRENT
Default 4 mA.
200)