National Instruments 9225 Manual

CALIBRATION PROCEDURE
NI 9225
3-Channel, 300 Vrms, 24-Bit, Simultaneous,
Channel-to-Channel Isolated Analog Input Module
This document contains the verification and adjustment procedures for the National Instruments
9225. For more information about calibration solutions, visit ni.com/calibration.
Contents
Software.................................................................................................................................... 1
Documentation.......................................................................................................................... 2
Test Equipment......................................................................................................................... 3
Test Conditions......................................................................................................................... 3
Initial Setup............................................................................................................................... 4
Verification ............................................................................................................................... 4
Accuracy Verification....................................................................................................... 5
Gain Matching Verification.............................................................................................. 6
Phase Matching Verification ............................................................................................ 8
Adjustment................................................................................................................................ 9
Accuracy Adjustment ....................................................................................................... 9
EEPROM Update ..................................................................................................................... 10
Reverification ........................................................................................................................... 10
Accuracy Under Calibration Conditions .................................................................................. 10
Where to Go for Support .......................................................................................................... 11
Software
Calibrating the NI 9225 requires the installation of NI-DAQmx 9.3 or later on the calibration
system. You can download NI-DAQmx from ni.com/downloads. NI-DAQmx supports
LabVIEW, LabWindows™/CVI™, ANSI C, and .NET. When you install NI-DAQmx, you only
need to install support for the application software that you intend to use.
ni.com/manuals
DeutschFrançais

2|ni.com | NI 9225 Calibration Procedure
Documentation
Consult the following documents for information about the NI 9225, NI-DAQmx, and your
application software. All documents are available on ni.com and help files install with the
software.
NI cDAQ-9174/9178 Quick Start Guide
NI-DAQmx installation and hardware setup
NI 9225 Operating Instructions and Specifications
NI 9225 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-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 a C enum to .NET enum mapping table

NI 9225 Calibration Procedure |© National Instruments |3
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
Test Conditions
The following setup and environmental conditions are required to ensure the NI 9225 meets
published specifications.
• Keep connections to the NI 9225 as short as possible. Long cables and wires act as
antennas, picking up extra noise that can affect measurements.
• Use shielded copper wire for all cable connections to the NI 9225. Use twisted-pairs wire
to eliminate noise and thermal offsets.
• Maintain an ambient temperature of 23 °C ±5 °C. The NI 9225 temperature will be greater
than the ambient temperature.
• Keep relative humidity below 80%.
• Allow a warm-up time of at least 10 minutes to ensure that the NI 9225 measurement
circuitry is at a stable operating temperature.
Table 1. Recommended Equipment
Equipment
Recommended
Model Where Used Requirements
Calibrator Fluke 5500A Accuracy,
Adjustment
Use a high-precision voltage
source with an accuracy
≤100 ppm.
Function
Generator
NI 4461 Gain Matching,
Phase Matching
Use a function generator capable
of sourcing both 1 kHz and
20 kHz ±10 Vpk AC sinusoidal
signals with amplitude
uncertainty of ±10%.
Chassis NI cDAQ-9178 All —

4|ni.com | NI 9225 Calibration Procedure
Initial Setup
Complete the following steps to set up the NI 9225.
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. Connect the ring lug to the ground terminal on the side of the NI cDAQ-9178 using
the ground screw.
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 Measurement & Automation Explorer (MAX).
8. Right-click the device name and select Self-Test to ensure that the module is working
properly.
Verification
The following performance verification procedures describe the sequence of operation and test
points required to verify the NI 9225 and assumes that adequate traceable uncertainties are
available for the calibration references.

NI 9225 Calibration Procedure |© National Instruments |5
Accuracy Verification
Complete the following procedure to determine the As-Found status of the NI 9225.
1. Set the calibrator to Standby mode (STBY).
2. Connect the NI 9225 to the calibrator as shown in Figure 1.
Figure 1. Accuracy Verification Connections
3. Set the calibrator voltage to a Test Point value indicated in Table 4.
4. Set the calibrator to Operate mode (OPR).
5. Acquire and average samples.
a. Create and configure an AI voltage task according to Table 2.
b. Configure the task timing according to Table 3.
c. Start the task.
d. Read samples from the NI 9225.
e. Average the samples.
f. Stop the task.
g. Clear the task.
Table 2. NI 9225 AI Voltage Task Configuration for Phase Matching
Physical Channels
Minimum
(Vrms)
Maximum
(Vrms)
Terminal
Configuration
AI0:3 -300 300 Differential
Table 3. NI 9225 Voltage Task Timing Configuration for Phase Matching
Sample Mode Samples Per Channel Rate (kS/s)
Finite Samples 4167 50
NI 9225
Calibrator
HI
LO
AI1
–
+
AI0
–
+
AI2
–
+

6|ni.com | NI 9225 Calibration Procedure
6. Compare the per-channel averages to the limits in Table 4.
7. Set the calibrator to Standby mode (STBY).
8. Repeat steps 3 through 7 for each test point in Table 4.
9. Disconnect the calibrator from the device.
Note The test limits listed in Table 4 are derived using the values in Table 17.
Gain Matching Verification
Complete the following procedure to determine the As-Found status of the NI 9225.
1. Connect the NI 9225 to the function generator as shown in Figure 2.
Figure 2. Gain Matching Verification Connections
2. Configure function generator according to Table 5.
Table 4. NI 9225 Verification Test Limits for Accuracy
Range Test Point 1-Year Limits
Min
(Vrms)
Max
(Vrms)Location
Value
(VDC)
Lower Limit
(VDC)
Upper Limit
(VDC)
-300 300
Max 403.75 403.431250 404.068750
Mid 0.00 -0.052275 0.052275
Min -403.75 -404.068750 -403.431250
Table 5. Function Generator Configuration for Gain Matching Verification
Signal Type Amplitude (Vpk)Frequency (kHz)
Sinewave 9 20
NI 9225
Function
Generator
HI
LO
AI1
–
+
AI0
–
+
AI2
–
+

NI 9225 Calibration Procedure |© National Instruments |7
3. Enable the function generator.
4. Acquire samples.
a. Create and configure an AI voltage according to Table 6.
b. Configure the task timing according to Table 7.
c. Start the task.
d. Read samples from the NI 9225. Record this measurement as AmplitudeAcq for each
channel. NI recommends using the Extract Single Tone Information VI to determine
the amplitude.
e. Stop the task.
f. Clear the task.
5. Calculate the gain for each channel using the AmplitudeAcq value.
6. Compare the channel-to-channel gain difference to the maximum limit of ±0.25 dB.
7. Disable the function generator.
8. Disconnect the function generator from the device.
If the Gain Matching verification procedure determines that the NI 9225 is outside of the limits,
refer to Where to Go for Support for assistance in returning the device to NI.
Table 6. NI 9225 Configuration Task for Gain Matching Verification
Physical Channels Terminal Configuration
AI0:2 Differential
Table 7. NI 9225 Configuration Task for Gain Matching Verification
Sample Mode Samples Per Channel Rate (kS/s)
Finite Samples 25000 50
Amplitude dB() 20 log10 ×AmplitudeAcq
9V
----------------------------------- 





=

8|ni.com | NI 9225 Calibration Procedure
Phase Matching Verification
Complete the following procedure to determine the As-Found status of the NI 9225.
1. Connect the NI 9225 to the function generator as shown in Figure 3.
Figure 3. Phase Matching Verification Connections
2. Configure function generator according to Table 8.
3. Set the function generator frequency to a value indicated in Table 11.
4. Enable the function generator.
5. Acquire samples.
a. Create and configure an AI voltage task according to Table 9.
b. Configure the task timing according to Table 10.
c. Start the task.
d. Read samples from the NI 9225.
e. Clear the task.
Table 8. Function Generator Configuration for Phase Matching Verification
Signal Type Amplitude (Vpk)
Sinewave 9
Table 9. NI 9225 Voltage Task Configuration for Phase Matching Verification
Physical Channels Terminal Configuration
AI0:2 Differential
Table 10. NI 9225 Voltage Task Timing Configuration for Phase Matching Verification
Sample Mode Samples Per Channel Rate (kS/s)
Finite Samples 25000 50
NI 9225
Function
Generator
HI
LO
AI1
–
+
AI0
–
+
AI2
–
+

NI 9225 Calibration Procedure |© National Instruments |9
6. Calculate the phase for each channel on the NI 9225. NI recommends using the Extract
Single Tone Information VI to calculate phase.
7. Compare the channel-to-channel phase difference to the limits in Table 11.
8. Repeat steps 2 through 7 for each test point in Table 11.
9. Disable the function generator.
10. Disconnect the function generator from the device.
If the Phase Matching verification procedure determines that the NI 9225 is outside of the limits,
refer to Where to Go for Support for assistance in returning the device to NI.
Adjustment
The following performance adjustment procedure describes the sequence of operation required
to adjust the NI 9225.
Accuracy Adjustment
Complete the following procedure to adjust the accuracy performance of the NI 9225.
1. Set the calibrator to Standby mode (STBY).
2. Connect the NI 9225 to the calibrator as shown in Figure 1.
3. Adjust the NI 9225.
a. Initialize a calibration session on the NI 9225. The default password is NI.
b. Input the external temperature in degrees Celsius.
c. Call the NI 9225 get C Series adjustment points function to obtain an array of
recommended calibration voltages for the NI 9225.
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 9225 adjustment function according to Table 12.
g. Set the calibrator to Standby mode (STBY).
Table 11. NI 9225 Verification Test Limits for Phase Matching
Generator Frequency (kHz) Phase Matching Channel-to-Channel Limit
1±0.035°
20 ±0.700°
Table 12. Adjustment Configuration
Physical Channel Reference Value
cDAQMod8/aixThe actual value of the voltage output of the calibrator

10 |ni.com | NI 9225 Calibration Procedure
h. Repeat steps d through g for each point in the array.
i. Close the calibration session.
4. Disconnect the NI 9225 from the calibrator.
EEPROM Update
When an adjustment procedure is completed, the NI 9225 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.
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 Test Conditions before returning your device to NI. Refer to Where to
Go for Support for assistance in returning the device to NI.
Accuracy Under Calibration Conditions
The values in the following table are based on calibrated scaling coefficients, which are stored
in the onboard EEPROM.
The following accuracy table is valid for calibration under the following conditions:
• Ambient temperature 23 °C ±5 °C
• NI 9225 installed in slot 8 of an NI cDAQ-9178 chassis
• Slots 1 through 7 of the NI cDAQ-9178 chassis are empty
Note For operational specifications, refer to the most recent NI 9225 Operating
Instructions and Specifications online at ni.com/manuals.
Table 13. NI 9225 Accuracy Under Calibration Conditions
Percent of Reading (Gain Error) Percent of Range* (Offset Error)
±0.066% ±0.0123% (±52.3 mV)
* Range equals 425 VDC