National Instruments USB-443 Series Manual

CALIBRATION PROCEDURE

NI USB-443x

This document contains information about calibrating the National Instruments USB-4431 and

USB-4432. These devices are referred to in this document as NI USB-443x. For more information about

calibration, visit ni.com/calibration.

Contents

Software Requirements........................................................................................................................ 2

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

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

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

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

Calibration Procedures......................................................................................................................... 4

Initial Setup.................................................................................................................................. 4

Changing Coupling on NI USB-443x Devices............................................................................ 5

Verification .................................................................................................................................. 6

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

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

AI AC Coupled Gain Accuracy Verification .............................................................. 7

AI DC Coupled Gain Accuracy Verification .............................................................. 8

Analog Output Performance Verification............................................................................ 10

AO Offset Verification for the NI USB-4431 Device ................................................ 10

AO Gain Verification for the NI USB-4431 Device .................................................. 11

Timebase Frequency Accuracy Verification ....................................................................... 12

Adjustment................................................................................................................................... 13

Analog Input Adjustment..................................................................................................... 13

Analog Output Adjustment for the NI USB-4431 Device................................................... 16

Where to Go for Support ..................................................................................................................... 18

ni.com/manuals

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NI USB-443x Calibration Procedure 2 ni.com

Software Requirements

Calibrating the NI USB-443xdevice requires installing NI-DAQmx 9.3 or later on the calibration

system. You can download the NI-DAQmx driver from ni.com/downloads. NI-DAQmx supports

conducting a 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.

Documentation Requirements

For information about NI-DAQmx and the NI USB-443x, you can consult the following documents:

•DAQ Getting Started guides—provides instructions for installing and configuring NI USB-443x

devices.

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

measurement concepts.

•NI USB-443x Specifications—provides the published specification values for the NI USB-443x.

Refer to the most recent NI USB-443x Specifications online at ni.com/manuals.

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

These documents are installed with NI-DAQmx. You can also download the latest versions from the

NI Web site at ni.com/manuals.

Calibration Interval

National Instruments recommends a calibration interval of one year for the NI USB-443x. Adjust the

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

©National Instruments Corporation 3 NI USB-443x Calibration Procedure

Test Equipment

Table 1 lists the equipment National Instruments recommends for calibrating the NI USB-443x.

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

given specifications.

Table 1. Recommended Equipment

Equipment Recommended Model

Parameter

Measured/

Adjusted Minimum Requirements

Calibrator Fluke 5700A AI AC Coupled

Gain

AI DC Coupled

Gain

AI Offset

Frequency Range: 1 kHz

Voltage Range: up to 9 Vpk

AC Voltage Accuracy: ± 0.03% at

1kHz

DC Voltage Accuracy:

±150 ppm at 9 V

±100 μV with 1 mA load current

Function Generator HP/Agilent 33250A Timebase

Frequency

Accuracy

Frequency Range: up to 10 kHz

Frequency Accuracy: ±5 ppm†

Voltage Range: up to 9 Vpk

Digital Multimeter NI 4071 AO Gain

AO Offset

DC Voltage Resolution: 1 μV

DC Voltage Accuracy at 3.15 V:

±150 ppm

BNC Shorting Cap

NI USB-4431:

quantity 4

NI USB-4432:

quantity 5

Pomona Electronics 5085 AI Offset Resistance: <1 Ω

BNC Cables:

quantity 6

Pomona Electronics 5697 All Characteristic Impedance: 50 Ω

BNC (Female) to

Banana Adapter

Pomona Electronics 1269 All

BNC T-Connectors:

quantity 4

Pomona Electronics 4896 AI Gain

AI Offset

Characteristic Impedance: 50 Ω

*AC accuracy is the sum of all errors, including percent of reading error and temperature error, but excluding percent of

range error.

†Frequency accuracy is the sum of all errors, including initial accuracy and stability errors.

NI USB-443x Calibration Procedure 4 ni.com

Test Conditions

The following setup and environmental conditions are required to ensure the NI USB-443x meets

published specifications:

• Keep connections to the NI USB-443xas short as possible. Long cables and wires act as antennae,

picking up extra noise that can affect measurements.

•Use50ΩBNC coaxial cables for all connections to the device.

• 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 30 minutes to ensure that the measurement circuitry of the

NI USB-443xis at a stable operating temperature.

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

instructions.

Calibration Procedures

The calibration process includes the following steps:

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

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

operating within the published specifications prior to adjustment.

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

automatically stores the calibration date on the EEPROM.

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

published specifications after adjustment.

Note Skip the AC coupled portion of the AI Offset Verification procedure if both of the following

apply:

• Your device is hardware revision C or earlier.

• You have never performed an analog input calibration adjustment according to this document.

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.

Note When a device is configured in MAX, it is assigned a device name. Each function call uses

this device name to determine which device to calibrate. This document uses Dev_name to refer to

the device name. In the following procedures, use the device name as it appears in MAX.

©National Instruments Corporation 5 NI USB-443x Calibration Procedure

Changing Coupling on NI USB-443x Devices

NI USB-443xdevices support both AC and DC coupling. After changing the coupling on a device from

DC to AC, wait 30 seconds for the inputs to settle. If samples are acquired before the 30 seconds has

elapsed, the acquired data may be distorted. This section illustrates a deterministic method for setting

the delay.

Figure 1. Implicitly Setting Configuration Settings with the DAQmx Start Task VI

When channel configuration settings are set in software, NI-DAQmx keeps track of the desired settings

and downloads them to hardware simultaneously when the DAQmx Start Task VI is called. This means

that in Figure 1, the settings on the hardware change when the DAQmx Start Task VI is called, and not

when they are set earlier. Therefore, there is no 30 seconds wait between setting the coupling on the

device and starting the acquisition.

For flexibility, NI-DAQmx gives you the ability to download channel configuration settings to hardware

at any point by calling the DAQmx Control Task VI with the commit option as shown in Figure 2. When

programmed this way, the DAQmx Control Task VI ensures that the wait occurs after the coupling

setting has changed on the device.

Figure 2. Explicitly Setting Configuration Settings with the DAQmx Control Task VI

Be sure to perform an explicit commit and wait 30 seconds whenever you change the coupling on an

NI USB-443xfrom DC to AC.

Note NI-DAQmx may initialize the coupling on an NI USB-443xto DC when the device first

powers on. Similarly, NI-DAQmx may set the coupling to DC at the end of the execution of one of

the calibration adjustment VIs. Perform the 30 seconds wait procedure described in this section when

performing an AC-coupled acquisition after the device is powered on, and after calling any of the

calibration adjustment VIs.

NI USB-443x Calibration Procedure 6 ni.com

Verification

This section provides instructions for verifying the NI USB-443x Specifications for gain, offset, and

frequency accuracy. 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 Limits in Tables 3, 4, 6, 8, 9, 11, 13, and 15 are for the specified calibration sample rates and

temperatures, and are based on the March 2011 edition of the NI USB-443x Specifications. For more

general specifications, refer to the most recent NI USB-443x Specifications online at ni.com/

manuals. If a more recent edition of the specifications is available, recalculate the limits based upon

the latest specifications.

Analog Input Performance Verification

This section verifies the analog input (AI) performance of NI USB-443xdevices. Refer to the

NI USB-443x Specifications for the number of channels and performance specifications.

AI Offset Verification

Note Skip the AC coupled portion of this procedure if both of the following apply:

• Your device is hardware revision C or earlier.

• You have never performed an analog input calibration adjustment according to this document.

Complete the following steps to verify the AI offset:

1. Connect a BNC shorting cap to the channel you want to verify on the device.

2. Using Figure 2 as a guide, create and configure an AI voltage task on the NI USB-443xas shown

in Table 2.

3. Acquire readings with the NI USB-443x.

4. Average all of the acquired samples.

Table 2. AI Offset Verification Configuration for NI USB-443x

Configuration Val ue

Minimum value –10.0

Maximum value 10.0

Terminal configuration Pseudodifferential

Acquisition mode Finite number of samples

Rate 102400.0

Samples per channel 65,536

Coupling DC

Physical channel Dev_name/aix*

*Dev_name is the name shown for the NI USB-443xin MAX. xrefers to the channel number.

©National Instruments Corporation 7 NI USB-443x Calibration Procedure

5. If verifying an NI USB-4431, compare the averaged value to the limits in Table 3. If verifying an

NI USB-4432, compare the averaged value to the limits in Table 4.

6. Repeat steps 1 through 5 for each analog input channel that you want to verify. Connect the BNC

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

parameter with the channel being verified.

NI recommends that you verify each channel, but you can save time by verifying only the channels

used in your application.

7. Repeat steps 1 through 6. In step 2, set the coupling parameter to AC.

Note Skip the AC coupled portion of this procedure if both of the following apply:

• Your device is hardware revision C or earlier.

• You have never performed an analog input calibration adjustment according to this document.

AI AC Coupled Gain Accuracy Verification

Complete the following steps to verify AC coupled gain accuracy:

1. Connect the output of the calibrator to the channel you want to verify on the device.

2. Output a 1 kHz, 6.36 Vrms AC signal from the calibrator.

Table 3. AI Offset Limits for NI USB-4431

Coupling

Device Input Offset

(One Year Limits)

Min (mV) Max (mV)

AC and DC –1.3 1.3

Table 4. AI Offset Limits for NI USB-4432

Coupling

Device Input Offset

(One Year Limits)

Min (mV) Max (mV)

AC and DC –3.2 3.2

NI USB-443x Calibration Procedure 8 ni.com

3. Using Figure 2 as a guide, create and configure an AI voltage task on the NI USB-443xas shown

in Table 5.

4. Acquire readings with the NI USB-443x.

5. Calculate the amplitude of the acquired 1 kHz fundamental tone in Vrms, and compare the

amplitude to the limits in Table 6.

6. Repeat steps 1 through 5 for each analog input channel that you want to verify. Connect the output

of the calibrator to the channel being verified in step 1. In step 3, replace aix in the physical

channel parameter with the channel being verified.

NI recommends that you verify each channel, but you can save time by verifying only the channels

used in your application.

AI DC Coupled Gain Accuracy Verification

Complete the following steps to verify DC coupled gain accuracy:

1. Connect the output of the calibrator to the channel you want to verify on the device.

2. Output 0 VDC from the calibrator.

Table 5. AI AC Coupled Gain Accuracy Verification Configuration for NI USB-443x

Configuration Val ue

Minimum value –10.0

Maximum value 10.0

Terminal configuration Pseudodifferential

Acquisition mode Finite number of samples

Rate 102400.0

Samples per channel 65,536

Coupling AC

Physical channel Dev_name/aix*

*Dev_name is the name shown for the NI USB-443xin MAX. xrefers to the channel number.

Table 6. AI AC Coupled Gain Accuracy Limits for NI USB-443x

Calibrator Output Amplitude (Vrms)

Device Input Amplitude

(One Year Limits)

Min (Vrms)Max (Vrms)

6.36 6.350 6.370

©National Instruments Corporation 9 NI USB-443x Calibration Procedure

3. Create and configure an AI voltage task on the NI USB-443xas shown in Table 7.

4. Acquire readings with the NI USB-443x.

5. Average all of the acquired samples. Record this value.

6. Repeat steps 1 through 5. In step 2, output 9 VDC instead of 0 VDC. Subtract the averaged value

measured for 0 VDC from the 9 VDC measurement.

7. Compare the calculated value to the DC coupled gain accuracy limits.

If verifying an NI USB-4431, compare the calculated value to the appropriate limits in Table 8. If

verifying an NI USB-4432, compare the calculated value to the appropriate limits in Table 9.

8. Repeat steps 1 through 5. In step 2, output –9 VDC instead of 9 VDC. Subtract the averaged value

measured for 0 VDC from the –9 VDC measurement.

Table 7. AI DC Coupled Gain Accuracy Verification Configuration for NI USB-443x

Configuration Val ue

Minimum value –10.0

Maximum value 10.0

Terminal configuration Pseudodifferential

Acquisition mode Finite number of samples

Rate 102400.0

Samples per channel 65,536

Coupling DC

Physical channel Dev_name/aix*

*Dev_name is the name shown for the NI USB-443xin MAX. xrefers to the channel number.

Table 8. AI DC Coupled Gain Accuracy Limits for NI USB-4431

Calibrator Output

Amplitude (VDC)

Device Input Amplitude

(One Year Limits)

Min (V) Max (V)

98.9856 9.0144

–9 –9.0144 –8.9856

Table 9. AI DC Coupled Gain Accuracy Limits for NI USB-4432

Calibrator Output

Amplitude (VDC)

Device Input Amplitude

(One Year Limits)

Min (V) Max (V)

98.982 9.018

–9 –9.018 –8.982

NI USB-443x Calibration Procedure 10 ni.com

9. Compare the calculated value to the DC coupled gain accuracy limits.

If verifying an NI USB-4431, compare the calculated value to the appropriate limits in Table 8. If

verifying an NI USB-4432, compare the calculated value to the appropriate limits in Table 9.

10. Repeat steps 1 through 9 for each analog input channel that you want to verify. Connect the output

of the calibrator to the channel being verified in step 1. In step 3, replace aixin the physical channel

parameter with the channel being verified.

NI recommends that you verify each channel, but you can save time by verifying only the channels

used in your application.

Analog Output Performance Verification

This section verifies the analog output (AO) performance of the NI USB-4431 device. Refer to the

NI USB-443x Specifications for the performance specifications.

AO Offset Verification for the NI USB-4431 Device

Complete the following steps to verify the AO offset:

1. Connect channel AO 0 on the device to the input of the multimeter.

2. Create and configure an AO voltage task on the NI USB-4431 as shown in Table 10.

3. Create an array of length 96,000. Set every element in the array to a value of 0.0. Write the array

to the AO task.

4. Start the AO task. The AO channel will output 0 V as long as the task is running because

regeneration mode is enabled and the task is configured to generate samples continuously.

5. Wait 100 ms. This compensates for the filter delay of the analog output channel.

6. Measure the DC voltage of channel AO 0 on the device using the lowest voltage range of the

multimeter that can measure approximately 100 mV. Record the measured offset, as it will be used

in the AO Gain Verification for the NI USB-4431 Device procedure.

Table 10. AO Offset Verification Configuration for NI USB-4431

Configuration Val ue

Minimum value –3.5

Maximum value 3.5

Terminal configuration Pseudodifferential

Acquisition mode Continuous samples

Rate 96000.0

Samples per channel 96,000

Regeneration mode Allow regeneration

Physical channel Dev_name/ao0*

*Dev_name is the name shown for the NI USB-4431 in MAX.

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