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CALIBRATION PROCEDURE
NI 9238
4-Channel, ±0.5 V, 24-Bit Simultaneous, Channel-to-Channel Isolated
Analog Input Module
This document contains the verification and adjustment procedures for the NI 9238. For more
information about calibration solutions, visit
Contents
Software.................................................................................................................................... 1
Documentation.......................................................................................................................... 2
Test Equipment......................................................................................................................... 2
Test Conditions......................................................................................................................... 3
Initial Setup............................................................................................................................... 3
Verification ............................................................................................................................... 4
Accuracy Verification....................................................................................................... 4
Adjustment................................................................................................................................ 6
EEPROM Update ..................................................................................................................... 6
Reverification ........................................................................................................................... 7
Where to Go for Support .......................................................................................................... 7
ni.com/calibration.
Software
Calibrating the NI 9238 requires the installation of NI-DAQmx 14.1 or later on the calibration
system. You can download NI-DAQmx from ni.com/downloads. NI-DAQmx supports
LabVIEW, LabWindows™/CVI™, ANSI C, Microsoft Visual C++, Microsoft Visual Basic
.NET, and Microsoft Visual C#. When you install NI-DAQmx, you only need to install support
for the application software that you intend to use.
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Documentation
Consult the following documents for information about the NI 9238, NI-DAQmx, and your
application software. All documents are available on
software.
NI cDAQ-9174/9178 Quick Start
NI-DAQmx installation and hardware setup
NI 9238 Operating Instructions and Specifications
NI 9238 specific information, specifications, and calibration interval
NI-DAQmx Readme
Operating system and application software support in NI-DAQmx
LabVIEW Help
LabVIEW programming concepts and reference information about NI-DAQmx
VIs and functions
ni.com and help files install with the
NI-DAQmx C Reference Help
Reference information for NI-DAQmx C functions and NI-DAQmx C properties
NI-DAQmx .NET Help Support for Visual Studio
Reference information for NI-DAQmx .NET methods and NI-DAQmx .NET
properties, key concepts, and mapping C enums to .NET enums
Test Equipment
Table 1 lists the equipment recommended for the performance verification and adjustment
procedures. If the recommended equipment is not available, select a substitute using the
requirements listed in Table 1.
Table 1. Recommended Equipment
Recommended
Equipment
Calibrator Fluke 5500A Use a high-precision voltage source with an accuracy
Model
Requirements
of ≤60 ppm and offset error ≤6µV.
Chassis NI cDAQ-9178 —
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Test Conditions
The following setup and environmental conditions are required to allow the NI 9238 to meet the
performance levels shown in Table 2:
• Keep connections to the NI 9238 as short as possible. Long cables and wires act as
antennas, picking up extra noise that can affect measurements.
• Verify that all connections to the NI 9238 are secure.
• Use shielded copper wire for all cable connections to the NI 9238. Use twisted-pairs wire
to eliminate noise and thermal offsets.
• Maintain an ambient temperature of 23 °C ± 5 °C.
• Keep relative humidity below 80%.
• Allow a warm-up time of at least 10 minutes to ensure that the NI 9238 measurement
circuitry is at a stable operating temperature.
Initial Setup
Refer to the NI cDAQ-9174/9178 Quick Start for information about how to install the software
and hardware and how to configure the device in Measurement & Automation Explorer (MAX).
Complete the following steps to set up the NI 9238.
1. Install NI-DAQmx.
2. Make sure the NI cDAQ-9178 power source is not connected.
3. Connect the NI cDAQ-9178 to the system safety ground.
a. Attach a ring lug to a 14 AWG (1.6 mm) wire.
b. Use the ground screw to connect the ring lug to the ground terminal on the side of the
NI cDAQ-9178.
c. Attach the other end of the wire to the system safety ground.
4. Install the module in slot 8 of the NI cDAQ-9178 chassis. Leave slots 1 through 7 of the
NI cDAQ-9178 chassis empty.
5. Connect the NI cDAQ-9178 chassis to your host computer.
6. Connect the power source to the NI cDAQ-9178 chassis.
7. Launch MAX.
8. Right-click the device name and select Self-Test to ensure that the module is working
properly.
NI 9238 Calibration Procedure | © National Instruments | 3
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Verification
Calibrator
NI 9238
AI3–
AI3+
AI2–
AI2+
AI1–
AI1+
AI0–
AI0+
LO
HI
The following performance verification procedure describes the sequence of operation and test
points required to verify the NI 9238. The verification procedure assumes that the calibration
references have traceable uncertainties that meet the requirements listed in the Test Equipment
section.
Accuracy Verification
Complete the following procedure to determine the As-Found status of the NI 9238.
1. Set the calibrator to Standby mode (STBY).
2. Connect the NI 9238 to the calibrator, as shown in Figure 1.
Figure 1. NI 9238 Calibration Connections
3. Set the calibrator voltage to a selected Test Point value in Table 2.
A properly functioning NI 9238, when calibrated according to the conditions described in
this document, can be expected to have gain and offset errors within the limits shown.
The following accuracy table is valid for calibration under the following conditions:
• Ambient temperature 23 °C ± 5 °C
• Slot 8 of the NI cDAQ-9178 chassis is occupied by the NI 9238
• Slots 1 through 7 of the NI cDAQ-9178 chassis are empty
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Table 2. NI 9238 Accuracy Verification Test Limits
Range
Minimum
(V)
Maximum
(V)
Test Point
(V)
Upper Limit
-0.5 0.5 -0.45 -0.44956 -0.45044
0 0.00006 -0.00006
0.45 0.45044 0.44956
Note Values in Table 2 should be used for calibration verification only. These
values only apply under the specific calibration conditions described in this
document, and are not to be construed as general operational specifications of the
NI 9238. For operational specifications, refer to the most recent NI 9238 Operating
Instructions and Specifications at
ni.com/manuals.
4. Set the calibrator to Operate mode (OPR).
5. Acquire and average samples.
a. Create and configure an AI voltage task according to Table 3.
1-Year Limits
(V)
Lower Limit
(V)
Table 3. NI 9238 Voltage Task Configuration
Physical Channels
Minimum (V) Maximum (V)
AI0:3 -0.5 0.5
b. Configure the task timing according to Table 4.
Table 4. NI 9238 Task Timing Configuration
Sample Mode Samples per Channel Rate (kS/s)
Finite Samples 5000 50
c. Start the task.
d. Read samples from the NI 9238.
e. Average the samples.
f. Clear the task.
6. Compare the per-channel averages to the limits in Table 2.
Range
7. Set the calibrator to Standby mode (STBY).
8. Repeat steps 3 through 7 for each test point in Table 2.
9. Disconnect the NI 9238 from the calibrator.
NI 9238 Calibration Procedure | © National Instruments | 5
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Adjustment
The following performance adjustment procedure describes the sequence of operation required
to adjust the NI 9238.
Complete the following procedure to adjust the accuracy performance of the NI 9238.
1. Set the calibrator to Standby mode (STBY).
2. Connect the NI 9238 to the calibrator, as shown in Figure 1.
3. Adjust the NI 9238.
a. Initialize a calibration session on the NI 9238. The default password is NI.
b. Input the external temperature in degrees Celsius using the set temperature C Series
function.
c. Call the NI 9238 get C Series adjustment points function to obtain an array of
recommended calibration voltages for the NI 9238.
d. Set the calibrator to a reference value determined by the array of recommended
calibration voltages.
e. Set the calibrator to Operate mode (OPR).
f. Call and configure the NI 9238 adjustment function according to Table 5.
Table 5. Accuracy Adjustment Configuration
Physical Channel Reference Value
cDAQMod8/aix A reference value from the array of adjustment points.
Note The module acquisition starts each time the adjust function is called.
g. Set the calibrator to Standby mode (STBY).
h. Repeat steps d through g for each calibration voltage in the array.
i. Close the calibration session.
j. Clear the task.
4. Disconnect the NI 9238 from the calibrator.
EEPROM Update
When an adjustment procedure is completed, the NI 9238 internal calibration memory
(EEPROM) is immediately updated.
If you do not want to perform an adjustment, you can update the calibration date and onboard
calibration temperature without making any adjustments by initializing an external calibration,
setting the C Series calibration temperature, and closing the external calibration.
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Reverification
Repeat the Verification section to determine the As-Left status of the device.
Note If any test fails Reverification after performing an adjustment, verify that you
have met the conditions listed in the Test Conditions section before returning your
device to NI. Refer to the Where to Go for Support section for assistance in returning
the device to NI.
Where to Go for Support
The National Instruments website is your complete resource for technical support. At ni.com/
support
self-help resources to email and phone assistance from NI Application Engineers.
Visit
other services.
Visit
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374757A-01 Jul15
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