©
National Instruments Corporation
15
NI 9219 Calibration Procedure
9.
Create an AI resistance channel on the NI 9219. Configure the channel according to Table 14.
10. Acquire 20 4-wire resistance readings with the NI 9219. Record the average of the readings as
channel
.
11. Perform the following calculation using the recorded
ref
and
channel
values.
12. Compare the calculation result to the Upper Limit and Lower Limit values in Table 15.
13. Clear the acquisition.
14. Disconnect the resistor from the device.
15. Repeat steps 1 through 14 for all test points and channels on the NI 9219. NI recommends that you
verify the values for all the iterations listed in Table 15 for each channel, but you can save time by
verifying only the values and channels used in your application.
4-Wire RTD Accuracy Verification
Complete the following steps to verify the 4-wire RTD accuracy of an NI 9219.
1.
Connect the NI 9219 to the resistor and the DMM as shown in Figure 8. Connect the sense leads
of the DMM as close as possible to the same point that the sense leads of the NI 9219 (HI and LO)
connect to the resistor to ensure that the DMM reference measurements include the same lead wire
resistance as the NI 9219 4-wire measurements.
Table 14.
NI 9219 Configuration for 4-Wire Resistance Accuracy Verification
Measurement
Type
Min (
)
Max (
)
Excitation
Source
Excitation
Value
Resistance
Config
ADC
Timing
Mode
Sample
Timing
Type
4-Wire
Resistance 1 k
0
1000
Internal
0.0005
4-Wire
High
Resolution
On
Demand
4-Wire
Resistance 10 k
10000
Table 15.
NI 9219 Verification Test Limits for 4-Wire Resistance Accuracy
Mode
Range
Test Point
1
–
Year Limits
Min (
)
Max
(k
)
Location
Value
Lower Limit (
)
Upper Limit (
)
4-Wire
Resistance 1 k
0
1.05
Max
845
±1%
–1.15
1.15
Min
20
±5%
–0.50
0.50
4-Wire
Resistance 10 k
0
10.5
Max
8450
±1%
–7.20
7.20
Min
20
±5%
–0.64
0.64
Accuracy
channel
ref
–
=
