National Instruments SCXI -1122 Manuale

CALIBRATION PROCEDURE

SCXI -1122

This document contains information and step-by-step instructions for

calibrating the National Instruments SCXI-1122 module.

Contents

Introduction............................................................................................. 2

What Is Calibration? ........................................................................ 2

Why Should You Calibrate? ............................................................ 2

How Often Should You Calibrate? .................................................. 2

Equipment and Other Test Requirements ............................................... 2

Test Equipment ................................................................................ 2

Instruments ............................................................................... 3

Connectors ................................................................................ 3

Software and Documentation........................................................... 3

Software.................................................................................... 3

Documentation.......................................................................... 3

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

Calibration............................................................................................... 4

Setting Up the Module..................................................................... 5

Verifying the Operation of the Module ........................................... 5

Verifying Analog Input Offsets ................................................ 5

Verifying Excitation Limits...................................................... 9

Adjusting the Module ...................................................................... 10

Adjusting Gain and Offset Errors............................................. 10

Adjusting Calibration Constants............................................... 13

Adjusting Excitation Limits...................................................... 14

Verifying Adjusted Values .............................................................. 15

Test Limits .............................................................................................. 15

™

SCXI-1122 Calibration Procedure 2 ni.com

Introduction

What Is Calibration?

Calibration consists of verifying the measurement accuracy of a module

and adjusting for any measurement error. Verification is measuring the

performance of the module and comparing these measurements to the

factory specifications. During calibration, you supply and read voltage

levels using external standards, then you adjust the module calibration

constants. The new calibration constants are stored in the EEPROM. These

calibration constants are loaded from memory as needed to adjust for the

error in the measurements taken by the module.

Why Should You Calibrate?

The accuracy of electronic components drifts with time and temperature,

which can affect measurement accuracy as a module ages. Calibration

restores these components to their specified accuracy and ensures that the

module still meets NI standards.

How Often Should You Calibrate?

The measurement requirements of your application determine how often

you must calibrate the SCXI-1122 module to maintain accuracy. NI

recommends that you perform a complete calibration at least once every

year. You can shorten this interval to 90 days or six months based on the

demands of your application.

Equipment and Other Test Requirements

This section describes the test equipment, software, documentation,

and test conditions required for calibrating the SCXI-1122 module.

Test Equipment

Calibration requires a high-precision voltage source with at least 50 ppm

accuracy, a multiranging 5 1/2-digit digital multimeter (DMM) with

15 ppm accuracy, a 15 Ω±10% resistor, and a 16-bit NI E Series data

acquisition (DAQ) device.

©National Instruments Corporation 3 SCXI-1122 Calibration Procedure

Instruments

NI recommends the following instruments for calibrating the SCXI-1122

module:

• Calibrator—Fluke 5700A

• DMM—NI 4060 or HP 34401A

If these instruments are not available, use the accuracy requirements listed

above to select substitute calibration instruments.

Connectors

If you do not have custom connection hardware, you need the following

equipment:

• SCXI-1322 terminal block

• Shielded 68-pin connector cable

• 50-pin ribbon cable

• 50-pin breakout box

• SCXI-1349 adapter

These components give easy access to the individual pins on the

SCXI-1122 module front and rear connectors.

Software and Documentation

This section describes the software and documentation you need to

calibrate the SCXI-1122 module.

Software

This calibration procedure requires the latest version of the Traditional

NI-DAQ (Legacy) driver software on the calibration system. The driver

supports a number of programming languages, including LabVIEW and

Measurement Studio. If you do not have the latest version of Traditional

NI-DAQ (Legacy), you can download it from the NI Web site at

ni.com/download. When you install the driver, you only need to install

support for the programming language used in your application.

Documentation

•Traditional NI-DAQ Function Reference Help

• Traditional NI-DAQ User Manual

The Traditional NI-DAQ Function Reference Help and the Traditional

NI-DAQ User Manual contain detailed information about using Traditional

NI-DAQ (Legacy). The help file includes detailed information about the

SCXI-1122 Calibration Procedure 4 ni.com

driver functions. You can access the help file by selecting Start»All

Programs»National Instruments»NI-DAQ»Traditional NI-DAQ

Function Reference Help.

The user manual provides instructions on installing and configuring

NI-DAQ devices. It also includes detailed information about creating

applications that use Traditional NI-DAQ (Legacy). You can access the user

manual by selecting Start»All Programs»National Instruments»

NI-DAQ»Traditional NI-DAQ User Manual.

These documents are your primary references for writing your calibration

utility. For more information about the products you are calibrating, refer

to the device documentation.

Test Conditions

Follow these guidelines to optimize the connections and environment

during calibration:

• Keep connections to the SCXI-1122 module and the terminal block

short. Long cables and wires act as antennae, picking up extra noise

and thermal offsets that can affect measurements.

• Use shielded copper wire for all cable connections to the device.

Use twisted-pair wire to eliminate noise and thermal offsets.

• Maintain the temperature between 18 °C and 28 °C.

• Keep relative humidity below 80%.

• Allow a warm-up time of at least 15 minutes for the SCXI-1122

module and 30 minutes for the E Series DAQ device to ensure the

measurement circuitry is at a stable operating temperature.

Calibration

The calibration process has the following steps:

1. Set up the SCXI-1122 module for verification.

2. Verify the existing operation of the module to determine whether the

module is operating within its test limits.

3. Adjust the module with respect to a known voltage source.

4. Verify that the module is operating within its test limits after

adjustments.

©National Instruments Corporation 5 SCXI-1122 Calibration Procedure

Setting Up the Module

Complete the following steps to set up the SCXI-1122 module for

verification:

1. Install the SCXI-1122 module in slot 4 of the SCXI chassis.

2. Connect a 68-to-68-pin cable between the SCXI-1122 module and the

E Series DAQ device.

3. Configure the hardware with Measurement & Automation Explorer

(MAX). For more information about configuring the calibration

system, refer to the E Series DAQ device and SCXI-1122 module

documentation.

Verifying the Operation of the Module

These verification procedures determine how well the SCXI-1122 module

is meeting its test limits. You can use this information to select the

appropriate calibration interval for your application.

Verifying Analog Input Offsets

Complete the following steps to verify the analog input offsets:

1. Read the Test Conditions section in this document.

2. Refer to Table 3 for the limits to verify. Although NI recommends

verifying all ranges and gains, you can save time by checking only

those ranges used in your application.

3. Ensure that the E Series DAQ device is connected to the SCXI-1122

module.

4. Call Calibrate_E_Series to minimize the uncertainty associated

with the E Series DAQ device. Set the following parameters:

•deviceNumber—The value assigned by MAX

•calOp—ND_SELF_CALIBRATE

•setOfCalConstants—ND_USER_EEPROM_AREA

•calRefVolts—0.0

5. Call AI_Configure to set the E Series DAQ device in bipolar mode.

Set the following parameters:

•deviceNumber—The value assigned by MAX

•chan—0

•inputMode—0

•inputRange—0

•polarity—0

•driveAIS—0

SCXI-1122 Calibration Procedure 6 ni.com

6. Call MIO_Config to enable dithering on the E Series DAQ device.

Set the following parameters:

•deviceNumber—The value assigned by MAX

•dither—1

•useAmux—0

7. Call SCXI_Configure_Filter to configure the filter mode of the

SCXI-1122 module. Set the following parameters:

•assigned bySCXIchassisId—The value assigned by MAX

•moduleSlot—1

•channel— –1

•filterMode—1

•freq—4.0

•cutoffDivDown—0

•and outClkDivDown—2

•ActualFreq—This is a return value

8. Call SCXI_Single_Chan_Setup to configure the SCXI-1122

module for single channel measurements. Set the following

parameters:

•SCXIchassisID—The value assigned by MAX

•moduleSlot—1

•moduleChan—0

•DAQdeviceNumber—The device number assigned by MAX for

the E Series DAQ device

9. Call SCXI_Calibrate_Setup to auto-zero the SCXI-1122 module.

Set the following parameters:

•SCXIchassisID—The value assigned by MAX

•moduleSlot—1

•calOp—2

10. Call SCXI_Set_Gain to set the selected gain on the SCXI-1122

module. Set the following parameters:

•SCXIchassisID—The value assigned by MAX

•moduleSlot—1

•channel— –1

•gain—The gain value you want to test

Acceptable gain values are listed in Table 3.

©National Instruments Corporation 7 SCXI-1122 Calibration Procedure

11. If you have an SCXI-1322 terminal block, connect the calibrator to the

CH0+ and CH0– inputs of the terminal block. If you are not using a

terminal block, connect the calibrator to analog input channel 0.

Refer to Table 1 to determine the pins on the 96-pin front connector

that correspond to the positive and negative inputs of the specified

channel. For example, the positive input for channel 0 is pin A32,

which is labeled CH0+. The negative input for channel 0 is pin C31,

which is labeled CH0–.

Table 1. SCXI-1122 Front Connector Pin Assignments

Pin Number Column A Column B Column C

32 NC CH0+ NC

31 RSVD NC CH0–

30 NC CH1+ NC

29 NC NC CH1–

28 NC CH2+ NC

27 NC NC CH2–

26 NC CH3+ NC

25 NC NC CH3–

24 NC CH4+ NC

23 IEX+ NC CH4–

22 NC CH5+ NC

21 IEX– NC CH5–

20 NC CH6+ NC

19 VEX+ NC CH6–

18 NC CH7+ NC

17 SENSE+ NC CH7–

16 NC CH8+ NC

15 SENSE– NC CH8–

14 NC CH9+ NC

13 VEX– NC CH9–

12 NC CH10+ NC

SCXI-1122 Calibration Procedure 8 ni.com

12. Set the calibrator voltage to the Test Point value in Table 3 that

corresponds to the gain from step 10.

13. Call DAQ_Op to retrieve measurement data from the SCXI-1122

module.

Set the following parameters:

•deviceNumber—The value assigned by MAX

•chan—0

•gain—1

•count—100

•sampleRate—100

The data is returned to the buffer variable.

14. Call SCXI_Scale to convert the acquired readings into scaled voltage

values. Set the following parameters:

•SCXIChassisID—The value assigned by MAX

•moduleSlot—0

•channel—0

•SCXIgain—The gain from step 10

•TBgain—1

•DAQBoard—The value assigned by MAX

11 VEX/2 NC CH10–

10 NC CH11+ NC

9NC NC CH11–

8NC CH12+ NC

7+5 V NC CH12–

6NC CH13+ NC

5NC NC CH13–

4NC CH14+ NC

3TEMP+ NC CH14–

2NC CH15+ NC

1TEMP– NC CH15–

NC — No connect

Table 1. SCXI-1122 Front Connector Pin Assignments (Continued)

Pin Number Column A Column B Column C

©National Instruments Corporation 9 SCXI-1122 Calibration Procedure

•DAQchannel—0

•DAQgain—1

•numPoints—100

Average the resulting scaled data to obtain the final voltage

measurement.

15. Compare the measurement result to the upper and lower limits shown

in Table 3. If the measurement value falls between the Upper Limit and

Lower Limit values, the SCXI-1122 module passed the test.

16. Repeat steps 5 through 15 for the two other test points of the gain

setting. You only need to check channel 0 on the SCXI-1122 module

because all inputs are multiplexed back through the same amplifier and

filter combination.

17. Repeat steps 5 through 16 for each of the remaining gain settings.

After you have checked all gains for Table 3, continue with step 18.

18. Repeat steps 4 through 17 using Table 3, but set the freq input

to 4000.0 in step 7.

Note If all channels fall within the upper and lower limits, the module does not need

adjustment.

You have completed verifying the analog input offsets of the SCXI-1122

module.

Verifying Excitation Limits

Complete the following steps to verify the excitation limits:

1. Connect a 15 Ωresistor between VEX+ and VEX– on the front of the

SCXI module.

Note If you are not using the SCXI-1322 terminal block, make sure that the SENSE+

terminal is connected to the VEX+ terminal and the SENSE– terminal to the VEX–

terminal.

2. Set the DMM to voltage mode and connect it across the resistor.

3. Compare the DMM reading to the upper and lower limits for voltage

excitation shown in Table 2. If the reading falls between the Upper

Limit and Lower Limit values, the SCXI-1122 module passed the test.

SCXI-1122 Calibration Procedure 10 ni.com

4. Set the DMM to current mode and connect it between the IEX+ and

IEX– pins of the SCXI-1122 module.

5. Compare the DMM reading to the upper and lower limits for the

current excitation shown in Table 2. If the reading falls between the

Upper Limit and Lower Limit values, the SCXI-1122 module passed

the test.

Adjusting the Module

This section contains three adjustment procedures: one for adjusting gain

and offset errors, one for adjusting calibration constants, and one for

adjusting excitation.

Adjusting Gain and Offset Errors

Complete the following steps to adjust gain and offset errors:

1. Ensure that the E Series DAQ device is connected to the SCXI-1122

module.

2. Call SCXI_Configure_Filter to configure the filter mode of the

SCXI-1122 module. Set the following parameters:

•SCXIchassisId—The value assigned by MAX

•moduleSlot—1

•channel— –1

•filterMode—1

•freq—4.0

•cutoffDivDown—0

•outClkDivDown—2

•ActualFreq—This is a return value

Table 2. Excitation Test Limits

Excitation

Type Test Point Upper Limit Lower Limit

Vo l t a g e 3.333 V 3.3343 V 3.3317 V

Current 1.00 mA 1.0004 mA 0.9996 mA

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