Vaisala FD12P - Manual (Page 83)

Chapter 4 _________________________________________________________________ Operation
VAISALA ________________________________________________________________________ 83
In the above example, alarm Limit 2 receives a new value, 300 m.
When the visibility now weakens below Limit 2, then the data
message (0 to 2) data status is set to 2. The visibility alarm is not
shown in the status message.
The 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 expressed in volt (V). The measurement
range is 0 to 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 (as also does the same increase in
the visibility indication).
RECEIVER CONTAMINATION LIMITS
WARNING LIMIT
( 300)
ALARM LIMIT ( 500) 600
ALARM LIMIT UPDATED
The receiver values are expressed in hertz (Hz). The measurement
range is from 0 to 10000 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 analog output mode and visibility range are set last. In the
logarithmic mode, the minimum visibility must be different from 0 as
LN(0) is not defined.
ANALOG OUTPUT MODE
0 = LINEAR 1 = LN ( 0)
ANALOG OUTPUT RANGE
MAX VISIBILITY
( 10000)
MIN VISIBILITY ( 50)
END OF CONFIGURATION