Vaisala PWD22 - Maintenance Commands; Sta

Chapter 5 ________________________________________________________________ Operation
VAISALA _______________________________________________________________________ 73
,
ln
ln
)ln()ln(
)ln()ln(
min
max
min
minmax
min
















=
−
−
=
VIS
VIS
VIS
VIS
VISVIS
VISVIS
X
i
i
coeff
where
VIS
i
=
Initial visibility value in meters.
VIS
min
=
Lowest visibility value specified in configuration
(for example 10 m or 100 m).
VIS
max
=
Corresponding maximum visibility value (for example
2000 m or 20000 m).
The corresponding DAC output LSB value is calculated from I
out
by
using DAC scale parameters.
Mode 3
Mode 3 is the non-linear Videograph mode . The visibility range from
100 m to 10000 m corresponds to the current range of 1 ... 0 mA.
Mode 4
Mode 4 is the non-linear Videograph mode . The visibility range from
180 m to 20000 m corresponds to the current range of 1 ... 0.1 mA.
Analog Output Calibration
The analog output is initially calibrated at the factory. The analog output
has two ranges, 0 ... 1 mA and 0 ... 20 mA. The range is selected
according to the jumper.
In the calibration command, the internal scaling factors for milliamperes
to hardware control bits are calculated.
PWD22/52 set two-bit patterns to the DAC circuit and asks for the
corresponding measured currents. If the higher current is less than
2 mA, PWD22/52 calculates the current range of 0 ... 1 mA. Otherwise, it
calculates the current range of 0 ... 20 mA.
To perform analog output calibration:
1. Connect a multimeter between the pink and the blue wires in
PWD22/52.
2. Give the ACAL command to PWD22/52.