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Chapter 5__________________________________________________________________ Operation
VAISALA ________________________________________________________________________ 79
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
X
min
range
out
where
I
=
Current that flows to analog output current sink.
out
I
=
Specified lowest output current value (e.g. 4 mA).
min
I
=
Current range specified
range
(e.g. I
range
−
ln(
VIS
)
ln(
=
i
X
−
coeff
ln(
VIS
)
ln(
max
where
VIS
=
Initial visibility value in meters.
i
VIS
=
Lowest visibility value specified in configuration
min
(e.g. 10 m or 100 m).
VIS
=
Corresponding maximum visibility value (e.g. 2000 m or
max
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
X
max
range
out
where
I
=
Current that flows to analog output current sink.
out
I
=
Specified highest output current value (e.g. 20 mA).
max
)
,
coeff
= 20 mA - 4 mA =16 mA)
VIS
i
ln
VIS
VIS
)
=
min
min
VIS
)
VIS
min
max
ln
VIS
min
)
,
coeff
,
by
out
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