Mode 1; Mode 2 - Vaisala PWD22/52 User Manual

USER'S GUIDE____________________________________________________________________
70 __________________________________________________________________ M210543EN-E

Mode 1

Mode 1 is the logarithmic mode and it uses ln(visibility) values for the
output. The calculation is the following:
(
I = + ⋅
I I
min range
out
where
I = Current that flows to analog output current sink.
out
I = Specified lowest output current value (for example 4 mA).
min
I = Current range specified
range
(for example I
−
ln( VIS )
=
i
X
coeff
−
VIS
ln( )
max
where
VIS = Initial visibility value in meters.
i
VIS = Lowest visibility value specified in configuration
min
(for example 10 m or 100 m).
VIS = Corresponding maximum visibility value (for example 2000
max
m or 20000 m).
The corresponding DAC output LSB value is calculated from I
using DAC scale parameters.

Mode 2

Mode 2 is the extinction mode, which gives lower output for higher
visibility. The maximum visibility must be higher than the minimum.
The corresponding currents are automatically handled so that the lower
current corresponds to the maximum visibility. The calculation is the
following:
(
I = − ⋅
I I
max range
out
where
I = Current that flows to analog output current sink.
out
I = Specified highest output current value (for example 20 mA).
max
I = Current range specified
range
(for example I
)
X ,
coeff
= 20 mA - 4 mA =16 mA)
range

VIS
 
ln
VIS
ln( VIS )

=
min

VIS
ln( )
VIS
 
min
ln
VIS

)
X ,
coeff
= 20 mA - 4 mA =16 mA)
range

 
i

min
,

 
max

min
by
out