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NI 9219 Calibration Procedure
2.
Acquire an
Ω
TopHalfDMM
measurement.
a.
Create an AI voltage task in the 1 V range on the NI 9219.
b.
Commit the task to place the NI 9219 in voltage mode. This prevents the module from
interfering with the resistance measurements of the DMM.
c.
Configure the DMM for a 4-wire resistance measurement in the appropriate range
according to the test point from Table 25.
d.
Enable Auto Zero on the DMM.
e.
Acquire a resistance reading with the DMM. Record this measurement as
Ω
TopHalfDMM
.
f.
Clear the task.
3.
Reconnect the DMM as shown in Figure 9. To minimize mismatch between the NI 9219
and the DMM, connect the
Ω
HI
and
Ω
senseHI
leads of the DMM as close as possible to the
same point where the LO lead from the NI 9219 connects to the resistor and the
Ω
LO
and
the
Ω
senseLO
leads of the DMM directly to the spring-terminal connector of the NI 9219.
Figure 9.
3-Wire RTD Accuracy Verification Connections to the NI 9219
4.
Acquire an
Ω
BottomHalfDMM
measurement.
a.
Create an AI voltage task in the 1 V range on the NI 9219.
b.
Commit the task to place the NI 9219 in voltage mode. This prevents the module from
interfering with the resistance measurements of the DMM.
c.
Configure the DMM for a 4-wire resistance measurement in the 100
Ω
range or the
smallest range available.
d.
Enable Auto Zero on the DMM.
e.
Acquire a resistance reading with the DMM. Record this measurement as
Ω
BottomHalfDMM
.
f.
Disconnect the DMM from the resistor and the NI 9219.
g.
Clear the task.
5.
Calculate the DMM measurement of the 3-wire system from the following equation.
R
TestPoint
Ω
HI
LO
DMM
Ω
S
EN
S
E
HI
LO
NI 9219
EX+ (3)
LO (6)
EX– (5)
Ch
x
Ω
ref
Ω
TopHalfDMM
2
Ω
BottomHalfDMM
×
–
(
)
=