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National Instruments
11
SCXI-1503 Calibration Procedure
17. Apply the calculated scaling coefficients,
c
0
and
c
1
to the DMM measurement using the following
formula:
18. Compare the average scaled DMM reading with the test limit shown in Table 2.
19. Stop and then clear the DAQmx task.
20. Repeat steps 9 through 19 for each test point.
21. Repeat steps 9 through 20 with an input range of ±100 mV and a gain of 100.
Note
The combined DAQ/SCXI-1503 scaling coefficients,
b
0
and
b
1
, will not change for each test
point, but each channel and gain will have different scaling coefficients. Recalculate
c
0
and
c
1
each
time a channel and/or gain changes.
22. Repeat steps 9 through 21 for the remaining channels.
Verifying the Excitation Current
Complete the following steps to verify the excitation current of the SCXI-1503:
1.
Connect IEX
x
+ and IEX
x
- to the DMM current input where
x
is a channel value from 0 to 15.
Note
Ensure that all switches on the SCXI-1306 are in the off position as shown in Figure 3.
2.
Configure the DMM to do a current measurement with a range of 100
A and an accuracy of 15 nA
or better at 100
A.
Note
The PXI-4071 can measure up to 105
A in the 100
A range.
3.
Create an AI voltage channel and configure it to use internal excitation by setting the AI.Excit.Src
to internal and then read the excitation current value from the AI.Excit.Val property node. Save this
value to DUT IEX.
4.
Configure the DMM to get current measurement results. Save this value to DMM Reading.
5.
Calculate the excitation error using the following formula:
6.
Compare the calculated excitation error with the limit IEx Accuracy = ±0.05%.
7.
Clear the DAQmx task.
8.
Repeat steps 1 through 7 to verify all other channels.
Adjustment
Following the adjustment procedure automatically updates the calibration date and temperature in the
EEPROM of the SCXI-1503.
Note
National Instruments recommends a complete adjustment of your module to renew the
calibration interval. However, if you do not want to perform an adjustment, you can update the
calibration date and onboard calibration temperature without making any adjustments by calling only
the DAQmx Initialize External Calibration and DAQmx Close External Calibration VIs.
Adjustment corrects the following SCXI-1503 specifications:
•
Analog input.
•
Excitation current.
Scaled DMM Reading
DMM Reading
c
1
c
0
+
=
IEx Accuracy
DUT IEx
DMM Reading
-----------------------------------
1
–
100
=