2.6 D/A Conversion Operations
The D/A converters on PISO-DA/PIO-DA 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 P
ISO-DA/PIO-DA 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 e10 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
PIO-DA/PISO-DA Series User Manual (Ver.2.9, Feb. 2011, PMH-009-29 )
21
