PEX/PIO/PISO-DA Series Card
Analog Output Boards
User Manual/ Ver. 3.1/ Oct. 2013/ PMH-0010-31/ Page: 25
2.6
D/A Conversion Operations
The D/A converters on PEX-DA and PISO/PIO-DAxU series cards use 14-bit resolution, so the
digital data values range from 0x0000 to 0x3fff. The hardware is designed to output voltage
in a range from -10.1 ~ +10.1 volts, as follows:
0x0000
about
–
10.1 volts
0x3FFF
about +10.1 volts
In a conventional design, there will be some VRs that need to be adjusted so that the voltage
output for 0x0000 = -10.0 V and 0x3fff = +10.0 V. In addition, these VRs also have to be
adjusted so that the current output for 0x1fff = 0 mA and 0x3fff = 20 mA. In conventional
designs, these VRs are commonly used for voltage/current output, so the user has to perform
some calibration when changing from voltage to current. Also, if these VRs are changed, the
user has to re-perform the calibration. This procedure is complex and creates a heavy
workload.
The PEX-DA and P
ISO/PIO-DAxU series uses software calibration to replace this
complex procedure in the following manner:
For
each
voltage
output
channel, find two hex values
MaxV[n] and MinV[n] (stored
in the onboard EEPROM).
MaxV[n] is mapped to exactly
+10 V and MinV[n] is mapped
to exactly
–
10 V.
For
each
current
output
channel, also find two hex
values MaxI[n] and MinI[n]
(stored
in
the
onboard
EEPROM). MaxI[n] is mapped
to exactly 20 mA and MinI[n] is
mapped to exactly 0 mA.
Ideal / Actual
0X0000
0X3FFF
+10.1V / +10.?V
Calibration
-10.0V
+10.0V
MaxV[n]
MinV[n]
Hex Value
-10.1V / -10.?V
DaValue
Vout / Iout
MinI[n]
MaxI[n]
0mA
20mA
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