National Instruments 449 Series Manual

NI 449x Calibration Procedure

This document contains information about calibrating the National Instruments 449x devices.

For more information about calibration, visit ni.com/calibration.

Contents

Software Requirements............................................................................................................. 1

Documentation Requirements .................................................................................................. 2

Calibration Interval................................................................................................................... 2

Test Equipment......................................................................................................................... 3

Test Conditions......................................................................................................................... 4

Calibration Procedures ............................................................................................................. 5

Initial Setup....................................................................................................................... 5

Self-Calibration ................................................................................................................5

Verification ....................................................................................................................... 5

Analog Input Performance Verification ................................................................... 6

AI Offset Verification....................................................................................... 6

AI AC Coupled Gain Accuracy Verification ................................................... 8

AI Flatness Verification.................................................................................... 10

AI DC Coupled Gain Accuracy Verification ................................................... 12

Timebase Frequency Accuracy Verification (Optional) .......................................... 14

Adjustment........................................................................................................................ 15

Analog Input Adjustment for NI 4495/4496/4498 Devices ..................................... 15

Analog Input Adjustment for NI 4492/4497/4499 Devices ..................................... 17

Updating the Calibration Date and Time without Performing Adjustment.............. 20

Where to Go for Support .......................................................................................................... 21

Software Requirements

Calibrating the NI 4492/4497/4499 requires NI-DAQmx 9.2 or later. Calibrating the

NI 4495/4496/4498 requires NI-DAQmx 8.8 or later. You can download the NI-DAQmx driver

from ni.com/downloads. NI-DAQmx supports Self-Calibration and External Calibration in

several programming language application development environments (ADEs). When you

install NI-DAQmx, you only need to install support for the ADE that you intend to use.

ni.com/manuals

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2|ni.com |NI 449xCalibration Procedure

Documentation Requirements

For information about NI-DAQmx and the NI 449x, you can consult the following documents:

•DAQ Getting Started guides—provide instructions for installing and configuring NI 449x

devices.

•NI-DAQmx C Reference Help—contains the C reference and general information about

measurement concepts.

•NI 449x Specifications—includes detailed information about NI 449x devices and provides

the published specification values for the NI 449x. Refer to the most recent NI 449x

Specifications online at ni.com/manuals.

•NI-DAQmx Help—includes information about creating applications that use NI-DAQmx.

The DAQ Getting Started guides, NI-DAQmx C Reference Help, and NI-DAQmx Help are

installed with NI-DAQmx. You can also download the latest versions from the NI website at

ni.com/manuals.

Calibration Interval

National Instruments recommends an external calibration interval of one year for the NI 449x.

Additionally, self-calibration can be performed as desired, but is recommended when the

operating temperature exceeds 5 °C from the operating temperature of the previous calibration.

This temperature can be queried from the module upon command. Adjust the recommended

calibration interval based on the measurement accuracy demands of your application.

NI 449xCalibration Procedure | © National Instruments | 3

Test Equipment

National Instruments recommends that you use the equipment in Table 1 for calibrating the

NI 449x.

Table 1. Recommended Equipment

Equipment

Recommended

Model

Parameter

Measured Minimum Requirements

Calibrator Fluke 5700A AI AC

coupled

gain

AI flatness

Frequency Range:

20 Hz to 92.2 kHz

Voltage Range: up to 9 Vpk

AC Accuracy: ±0.05%*,

20 Hz to 95 kHz

Function Generator†Agilent 33250A Timebase

frequency†

Frequency Range: up to

10 kHz

Frequency Accuracy:

±2 ppm*

Voltage Range: up to 9 Vpk

Voltage Source NI PXI-6233 AI DC

coupled

gain

Voltage Range: ±10 V

Output isolated from

EARTH ground‡

Digital Multimeter NI PXI-4070 AI DC

coupled

gain

Voltage Measurement

Accuracy: ±200 ppm*

InfiniBand to BNC

Cable

NI 4495/4496/4497/

4498/4499: quantity 2

NI PXIe-4492:

quantity 1

NI SHB4X-8BNC All N/A

BNC Shorting Cap

NI 4495/4496/4497/

4498/4499: quantity 16

NI PXIe-4492:

quantity 8

Pomona

Electronics 5085

AI offset Resistance: ≤50 Ω

4|ni.com |NI 449xCalibration Procedure

If the recommended equipment is not available, select a substitute calibration standard that

meets the given specifications.

Test Conditions

The following setup and environmental conditions are required to ensure the NI 449x meets

published specifications:

• Keep connections to the NI 449x as short as possible. Long cables and wires act as

antennae, picking up extra noise that can affect measurements.

• Use the InfiniBand to BNC cable to connect signals to the NI 449x.

• Keep relative humidity between 10% and 80%, noncondensing, or consult the device

documentation for the optimum relative humidity.

• Maintain the ambient temperature between 18 °C and 28 °C, or refer to the device

specifications for the optimum temperature range.

• Allow a warm-up time of at least 15 minutes to ensure that the measurement circuitry is at

a stable operating temperature.

• Allow a warm-up time for all of the instruments and equipment according to the

manufacturer instructions.

BNC Cable

NI 4495/4496/4497/

4498/4499: quantity 17

NI PXIe-4492:

quantity 9

Pomona

Electronics 5697

All Characteristic Impedance:

50 Ω

BNC T-Connector

NI 4495/4496/4497/

4498/4499: quantity 15

NI PXIe-4492:

quantity 7

Pomona

Electronics 4896

Adjustment Characteristic Impedance:

50 Ω

BNC to Banana

Adapter

quantity 1

Pomona

Electronics 1269

AI gain N/A

*Accuracy is the sum of all errors, including initial accuracy and stability errors.

†Timebase frequency verification is optional.

‡The NI 449x is not isolated from EARTH ground. Isolation is required in the voltage source to avoid

the creation of a ground loop that could potentially degrade the DC measurement accuracy. Voltage

accuracy of the source is not a requirement because of the use of the digital multimeter in parallel.

Table 1. Recommended Equipment (Continued)

Equipment

Recommended

Model

Parameter

Measured Minimum Requirements

NI 449xCalibration Procedure | © National Instruments | 5

Calibration Procedures

The calibration process includes the following steps:

1. Initial Setup—Install the device and configure it in Measurement & Automation Explorer

(MAX).

2. Self-Calibration—Adjust the self-calibration constants of the device.

3. Verification—Verify the existing operation of the device. This step confirms whether the

device is operating within the published specifications prior to adjustment.

4. Adjustment—Adjust the calibration constants of the device. The adjustment procedure

automatically stores the calibration date on the EEPROM.

5. Reverification—Repeat the verification procedure to ensure that the device is operating

within the published specifications after adjustment.

These procedures are described in more detail in the following sections.

Initial Setup

Refer to the DAQ Getting Started guides for information about how to install the software and

hardware and how to configure the device in MAX.

Self-Calibration

The NI 449x includes precise internal circuits and references used during self-calibration to

adjust for any errors caused by short-term fluctuations in the environment. Self-calibration does

not require external signal connections.

Note Allow a 15 minute warm-up period before you begin self-calibration.

Initiate self-calibration from MAX. To initiate self-calibration, complete the following steps:

1. Launch MAX.

2. Select My System»Devices and Interfaces.

3. Select the device that you want to self-calibrate.

4. Initiate self-calibration in one of the following ways:

•ClickSelf-Calibrate in the upper right corner of the window.

• Right-click the device name under Devices and Interfaces, and select Self-Calibrate

from the drop-down menu.

Verification

This section provides instructions for verifying the NI 449x specifications. By completing this

procedure, you can see how device accuracy has drifted over time, which helps you determine

the appropriate calibration interval for your application.

Note Test limits in Tables 3 through 8, and Tables 13 through 15 are based upon the

May 2012 edition of the NI 449x Specifications. Refer to the most recent NI 449x

Specifications online at ni.com/manuals.

6|ni.com |NI 449xCalibration Procedure

Analog Input Performance Verification

This section verifies the analog input (AI) performance of all NI 449x devices. Refer to the

NI 449x Specifications for the number of channels and performance specifications.

AI Offset Verification

Complete the following steps to verify the AI offset:

1. Connect a BNC shorting cap to channel AI 0 on the device and wait 5 seconds for the inputs

to settle.

2. Create and configure an AI voltage task on the NI 449x as shown in Table 2.

3. If verifying an NI 4492/4497/4499 and the coupling changes from DC to AC, commit the

configuration using the DAQmx Control Task VI and wait 5 seconds for the input to settle.

4. Start the task.

5. Acquire readings with the NI 449x.

6. Stop and clear the task.

7. Average all of the acquired samples.

Table 2. NI 449x AI Offset Verification Configuration

Configuration Value

Minimum value –10.0

Maximum value 10.0

Terminal configuration Pseudodifferential

Acquisition mode Finite number of samples

Rate 204,800.0

Samples per channel 102,400

Gain 0 (dB)

Physical channel Dev_name/ai0*

Coupling NI 4492: AC or DC

NI 4495: DC

NI 4496: AC

NI 4497: AC or DC

NI 4498: AC

NI 4499: AC or DC

*Dev_name is the name shown for the NI 449x in MAX.

NI 449xCalibration Procedure | © National Instruments | 7

If verifying an NI 4496/4498, compare this value to the appropriate limits in Table 3. The

average is the offset for channel AI 0 at the 0 dB gain setting.

If verifying an NI 4495, compare this value to the limits in Table 4. The average is the offset

for channel AI 0 at the 0 dB gain setting.

If verifying an NI 4492/4497/4499, compare this value to the appropriate limits in Table 5.

The average is the offset for channel AI 0 at the 0 dB gain setting, at the 204.8 kS/s sample

rate, in the selected coupling mode.

8. Repeat steps 2 through 7 for each gain setting that your device supports. Refer to Table 6

for the gain settings supported by NI 449x devices. When performing step 2, adjust the gain

parameter appropriately.

Table 3. AI Offset Limits for NI 4496/4498

As Found Test Limit As Left Test Limit

Min (mV) Max (mV) Min (mV) Max (mV)

–2 2–0.5 0.5

Table 4. AI Offset Limits for NI 4495

As Found Test Limit As Left Test Limit

Min (mV) Max (mV) Min (mV) Max (mV)

–0.5 0.5 –0.25 0.25

Table 5. AI Offset Limits for NI 4492/4497/4499

Coupling

As Found Test Limit As Left Test Limit

Min (mV) Max (mV) Min (mV) Max (mV)

AC –10 10 –0.5 0.5

DC –0.5 0.5 –0.25 0.25

Table 6. Supported Gain Settings

Device Gain Settings

NI 4492

0 dB, 20 dB

NI 4495

NI 4496

NI 4497

NI 4498

0 dB, 10 dB, 20 dB, 30 dB

NI 4499

8|ni.com |NI 449xCalibration Procedure

If verifying an NI 4492/4497/4499, separately verify AC and DC coupling for each

supported gain setting including 0 dB at sample rates of 102.4 kS/s and 204.8 kS/s. Refer

to Table 6 for the gain settings supported by supported by NI 449x devices.

9. Repeat steps 1 through 8 for all input channels on the device. Connect the BNC shorting

cap to the channel being verified in step 1. In step 2, replace ai0 in the physical channel

parameter with the channel being verified.

AI AC Coupled Gain Accuracy Verification

Note This section does not apply to the NI 4495. Skip this section if verifying an

NI 4495.

Complete the following steps to verify AC coupled gain accuracy:

1. Connect the output of the calibrator to channel AI 0 on the device.

2. If verifying an NI 4496/4498, configure the calibrator to generate a tone with the amplitude

and frequency listed in the 0 dB gain row of Table 7. Wait 5 seconds for the inputs to settle.

If verifying an NI 4492/4497/4499, configure the calibrator to generate a tone with the

amplitude and frequency listed in the 0 dB gain row of Table 8. Wait 5 seconds for the

inputs to settle.

Table 7. AI AC Coupled Gain Accuracy Limits for NI 4496/4498

Device

Gain

Calibrator

Output

As Found

Test Limit

As Left

Test Limit

Amplitude

(Vrms)

Frequency

(Hz)

Min

(Vrms)

Max

(Vrms)

Min

(Vrms)

Max

(Vrms)

0 dB 6.36 1000 6.287 6.434 6.323 6.397

10 dB 2.12 1000 2.096 2.145 2.108 2.132

20 dB 0.636 1000 0.6287 0.6434 0.6323 0.6397

30 dB 0.212 1000 0.2096 0.2145 0.2108 0.2132

Table 8. AI AC Coupled Gain Accuracy Limits for NI 4492/4497/4499

Device

Gain

Calibrator

Output

As Found

Test Limit

As left

Test Limit

Amplitude

(Vrms)

Frequency

(Hz)

Min

(Vrms)

Max

(Vrms)

Min

(Vrms)

Max

(Vrms)

0 dB 6.36 1000 6.323 6.397 6.342 6.378

10 dB 2.12 1000 2.108 2.132 2.114 2.126

20 dB 0.636 1000 0.6323 0.6397 0.6342 0.6378

30 dB 0.212 1000 0.2108 0.2132 0.2114 0.2126

NI 449xCalibration Procedure | © National Instruments | 9

3. Create and configure an AI voltage task on the NI 4492/4496/4497/4498/4499 as shown in

Table 9.

4. If verifying an NI 4492/4497/4499 and the coupling changes from DC to AC, commit the

configuration using the DAQmx Control Task VI and wait 5 seconds for the input to settle.

5. Start the task.

6. Acquire readings with the NI 4492/4496/4497/4498/4499.

7. Stop and clear the task.

8. Calculate the rms amplitude of the acquired fundamental harmonic. Compare this

amplitude to the appropriate voltage limits in Table 7 for the NI 4496/4498 or Table 8 for

the NI 4492/4497/4499. The calculated amplitude is used to verify the AC coupled gain

accuracy of channel AI 0 at the 0 dB gain setting, at the 204.8 kS/s sample rate.

9. If verifying an NI 4496/4498, repeat steps 2 through 8 for each gain setting that your device

supports. Refer to Table 10 for the gain settings supported by NI 449x devices. In step 2,

change the output of the calibrator based on the gain setting that is being verified. Table 7

lists the amplitude and frequency to use for each gain setting. When performing step 3,

adjust the gain parameter appropriately.

Table 9. NI 4492/4496/4497/4498/4499 AI AC Coupled Gain Accuracy

Verification Configuration

Configuration Value

Minimum value –10.0

Maximum value 10.0

Terminal configuration Pseudodifferential

Acquisition mode Finite number of samples

Rate 204,800.0

Samples per channel 102,400

Gain 0 (dB)

Physical channel Dev_name/ai0*

Coupling AC

*Dev_name is the name shown for the NI 449x in MAX.

10 |ni.com |NI 449xCalibration Procedure

If verifying an NI 4492/4497/4499, repeat steps 2 through 8 for each gain setting that your

device supports. Refer to Table 10 for the gain settings supported by NI 449x devices. For

each gain setting, including 0 dB, separately verify at sample rates of 102.4 kS/s and

204.8 kS/s. In step 2, change the output of the calibrator based on the gain setting that is

being verified. Table 8 lists the amplitude and frequency to use for each gain setting. When

performing step 3, adjust the gain and sample rate parameters appropriately.

10. Repeat steps 1 through 9 for all analog input channels on the device. Connect the output of

the calibrator to the channel being verified during step 1. In step 3, replace ai0 in the

physical channel parameter with the channel being verified.

AI Flatness Verification

Complete the following steps to verify the AI flatness:

1. Connect the output of the calibrator to channel AI 0 on the device.

2. If verifying an NI 4495/4496/4498, configure the calibrator to generate a tone with the

amplitude and frequency listed in the 0 dB gain row of Table 7. Wait 5 seconds for the

inputs to settle.

If verifying an NI 4492/4497/4499, configure the calibrator to generate a tone with the

amplitude and frequency listed in the 0 dB gain row of Table 8. Wait 5 seconds for the

inputs to settle.

3. Create and configure an AI voltage task on the NI 449x as shown in Table 11.

Table 10. NI 4492/4496/4497/4498/4499 Supported Gain Settings

Device Gain Settings

NI 4492

0 dB, 20 dBNI 4496

NI 4497

NI 4498

0 dB, 10 dB, 20 dB, 30 dB

NI 4499

Table 11. NI 449x AI Flatness Verification Configuration

Configuration Value

Minimum value –10.0

Maximum value 10.0

Terminal configuration Pseudodifferential

Acquisition mode Finite number of samples

Rate 204,800.0

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