Mode 3; Mode 4; Analog Output Calibration - Vaisala PWD22/52 User Manual

Chapter 5 ________________________________________________________________ Operation
VAISALA _______________________________________________________________________ 71
−
ln( VIS )
=
i
X
coeff
−
ln( VIS )
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
max
2000 m or 20000 m).
The corresponding DAC output LSB value is calculated from I
using DAC scale parameters.

Mode 3

Mode 3 is the Videograph mode that is non-linear. The visibility range
from 100 m to 10000 m corresponds to the current range of 1 ... 0 mA.

Mode 4

Mode 4 is the Videograph mode that is non-linear. 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.
The analog output calibration procedure is the following:
1. Connect a multimeter between the pink and the blue wires in
PWD22/52.
2. Give the ACAL command to PWD22/52.

VIS
 
ln
VIS
ln( VIS )

=
min

ln( VIS )
VIS
 
min
ln
VIS


 
i

min
,

 
max

min
by
out