National Instruments SCXI-1104/C Manuale

CALIBRATION PROCEDURE

SCXI -1104/C

For NI-DAQmx

This document contains information and instructions for calibrating the

National Instruments SCXI-1104/C signal conditioning module.

Contents

Conventions ............................................................................................ 2

Software .................................................................................................. 2

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

Calibration Interval ................................................................................. 3

Password ................................................................................................. 3

Test Equipment ....................................................................................... 4

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

Calibration Process ................................................................................. 5

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

Verification Procedure ..................................................................... 7

Adjustment Procedure...................................................................... 11

Verifying Adjusted Values .............................................................. 13

Test Limits .............................................................................................. 13

Gain and Offset................................................................................ 13

SCXI-1104/C Front and Rear Panel Diagrams ....................................... 14

World Wide Support and Services.......................................................... 17

™

SCXI-1104/C Calibration Procedure 2 ni.com

Conventions

The following conventions are used in this document:

»The »symbol leads you through nested menu items and dialog box options

to a final action. The sequence File»Page Setup»Options directs you to

pull down the File menu, select the Page Setup item, and select Options

from the last dialog box.

This icon denotes a note, which alerts you to important information.

bold Bold text denotes items that you must select or click in the software, such

as menu items and dialog box options. Bold text also denotes parameter

names.

italic Italic text denotes variables, emphasis, a cross-reference, or an introduction

to a key concept. Italic text also denotes text that is a placeholder for a word

or value that you must supply.

monospace Text in this font denotes text or characters that you should enter from the

keyboard, sections of code, programming examples, and syntax examples.

This font is also used for the proper names of disk drives, paths, directories,

programs, subprograms, subroutines, device names, functions, operations,

variables, filenames, and extensions.

monospace italic

Italic text in this font denotes text that is a placeholder for a word or value

that you must supply.

Software

The SCXI-1104/C calibration procedure requires the NI-DAQmx driver.

NI recommends using the latest driver that supports both your development

environment and the SCXI-1104/C. NI-DAQmx includes high-level

function calls to simplify the task of writing software to calibrate devices.

NI-DAQmx supports many programming languages, including LabVIEW,

LabWindows™/CVI™, C/C++, C#, and Visual Basic .NET.

©National Instruments 3 SCXI-1104/C Calibration Procedure

Documentation

The following documents are the primary references for writing your

calibration utility:

• The NI-DAQmx Help includes information about creating applications

that use NI-DAQmx.

• The NI-DAQmx C Reference Help includes information about the

functions in NI-DAQmx.

• The DAQ Getting Started guides include information about installing

and configuring NI-DAQmx devices.

You can access these documents by selecting

Start»All Programs»National Instruments»NI-DAQmx after installing

NI-DAQmx.

For more information about the SCXI-1104/C, refer to the SCXI-1104/C

User Manual. For information about installing and configuring SCXI

modules, refer to the SCXI Quick Start Guide.

Calibration Interval

Calibrate the SCXI-1104/C at a regular interval as defined by the

measurement accuracy requirements of your application. NI recommends

that you perform a complete calibration at least once every year. You can

shorten this interval based on the accuracy requirements of your

application.

Password

The default password for password-protected operations is NI.

SCXI-1104/C Calibration Procedure 4 ni.com

Test Equipment

NI recommends that you use the equipment in Table 1 to calibrate the

SCXI-1104/C. If these instruments are not available, use the requirements

listed in Table 1 to select a suitable substitute.

Note A complete SCXI-1104/C calibration system is illustrated in Figure 1 with a listing

of all the components required for calibrating the SCXI-1104/C.

Test Conditions

Follow these guidelines to optimize the connections and the environment

during calibration:

• Keep connections to the SCXI-1104/C as short as possible. Long

cables and wires can act as antennas, picking up extra noise and

thermal offsets that affect measurements.

• Use shielded copper wire for all cable connections to the

SCXI-1104/C. Use twisted-pair wire to eliminate noise and thermal

offsets.

• Maintain the ambient 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-1104/C and

30 minutes for the DAQ device to ensure that the measurement

circuitry is at a stable operating temperature.

Table 1. Test Equipment

Equipment

Recommended

Model Requirements

Calibrator Fluke 5700A 50 ppm

DAQ Device NI 6281 16-bit minimum

DMM NI 4070 6 1/2 digit, 15 ppm

Terminal Block SCXI-1300 —

©National Instruments 5 SCXI-1104/C Calibration Procedure

Calibration Process

The calibration process has the following steps:

1. Initial Setup—Configure the SCXI-1104/C for calibration.

2. Verification Procedure—Verify the existing operation of the

SCXI-1104/C. This step determines whether the SCXI-1104/C is

operating within its test limits.

3. Adjustment Procedure—Perform an external calibration that adjusts

the SCXI-1104/C calibration constants with respect to a known

voltage source.

4. Verifying Adjusted Values—Perform another verification to ensure

that the SCXI-1104/C is operating within its test limits after

adjustments.

Initial Setup

Complete the following steps to configure the SCXI-1104/C for

calibration:

1. Make sure that all the appropriate driver and application software is

installed.

2. Make sure all components involved in the calibration procedure are

powered off.

3. Assemble the SCXI-1104/C, SCXI chassis, terminal blocks, and DAQ

device as shown in Figure 1. You must cable the SCXI-1104/C directly

to the DAQ device. Install the SCXI-1104/C module in slot 1 of the

SCXI chassis.

SCXI-1104/C Calibration Procedure 6 ni.com

Figure 1. Calibration Components and Connections

4. Power on the SCXI chassis and the external computer.

5. You must configure the hardware properly with Measurement &

Automation Explorer (MAX). Refer to the SCXI Quick Start Guide for

details about configuring the SCXI chassis.

Note When you configure a device in MAX, the device is assigned a device identifier. In

this calibration document, the functions used for demonstrating the calibration process use

the device identifiers Dev1 for the DAQ device and SC1Mod1 for the SCXI-1104/C. If you

have more devices in your setup, use MAX to identify your DAQ device name.

1 SCXI-1300 Terminal Block

2 SCXI-1104/C Module

3 SCXI Chassis

4 SCXI-1349 Cable Adapter

5 Shielded 68-Pin Cable

6 NB1 Cable (50-Pin Ribbon Cable)

7 CB-50 Connector Block

8 Cable to DMM

9 Cable to Calibrator

10 Calibrator

11 DMM

12 DAQ Device

ADDRESS

SCXI1100

2468 10 12 1416 18 20 20 24 26 28 30 32 34 36 38 40 42 44 46 48 50

13 5 7 911 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49

©National Instruments 7 SCXI-1104/C Calibration Procedure

Verification Procedure

The verification procedure determines how well the SCXI-1104/C is

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

appropriate calibration interval for your application.

The SCXI-1104/C stores gain and offset calibration constants for each gain

setting per analog input channel. A complete verification of the inputs

involves measuring the accuracy at all possible gain settings on all channels

of the SCXI-1104/C.

To view the calibration VIs in LabVIEW, select Measurement

I/O»DAQmx - Data Acquisition»DAQmx Advanced»DAQmx

Calibration on the Functions palette. You can also use the Search button,

shown in Figure 2, to look for a specific VI.

Figure 2. DAQmx Calibration Palette and the Search Button

SCXI-1104/C Calibration Procedure 8 ni.com

Complete the following steps to verify the accuracy of each SCXI-1104/C

analog input channel:

1. Use the DAQmx Self Calibrate VI to verify the DAQ device. This VI

measures the onboard reference voltage of the DAQ device and adjusts

the self-calibration constants to account for any errors caused by

short-term fluctuations in the operating environment.

Note Throughout the verification procedure, refer to the function call parameters for the

LabVIEW input values.

2. Connect the calibrator output to pins CH– and CH+ for all channels.

Refer to the SCXI-1300/1301 Terminal Block Installation Guide for

connection instructions. If you are not using the recommended

SCXI-1300, refer to Table 4 for the front signal pin assignments of the

SCXI-1104/C. If the calibration signal source is floating, connect

CH – to the SCXI chassis ground using the ground lug available on the

SCXI terminal block.

3. Set the calibrator voltage to the desired test point indicated in Table 3.

4. Create a task using DAQmxCreateTask.

LabVIEW Block Diagram NI-DAQmx Function Call

Call DAQmxSelfCal with the

following parameter:

Device_Name:"Dev1"

LabVIEW Block Diagram NI-DAQmx Function Call

LabVIEW does not require

this step.

Call DAQmxCreateTask with the

following parameters:

taskName: "

AIVerificationTask

taskHandle: &taskHandle

©National Instruments 9 SCXI-1104/C Calibration Procedure

5. Add a voltage channel using the DAQmx Create Virtual Channel VI.

6. Configure timing for the voltage acquisition using the DAQmx

Timing VI.

7. Commit the verification changes using the DAQmx Control Task VI.

LabVIEW Block Diagram NI-DAQmx Function Call

Call DAQmxCreateAIVoltageChan with the

following parameters:

taskHandle: taskHandle

physicalChannel: "SC1Mod1/ai

"†

nameToAssignToChannel: "

myVoltageChannel

terminalConfig: DAQmx_Val_Cfg_Default

minVal: -45 V

maxVal: 45 V

units: DAQmx_Val_Volts

customScaleName: ""

†Where

refers to the channel you are verifying.

LabVIEW Block Diagram NI-DAQmx Function Call

Call DAQmxCfgSampClkTiming with the following

parameters:

taskHandle: taskHandle

source: ""

rate: 1000.0

activeEdge: DAQmx_Val_Rising

sampleMode: DAQmx_Val_FiniteSamps

sampsPerChan: 1000

LabVIEW Block Diagram NI-DAQmx Function Call

Call DAQmxTaskControl with the following

parameters:

taskHandle: taskHandle

action: DAQmx_Val_Task_Commit

SCXI-1104/C Calibration Procedure 10 ni.com

8. For each new test point, use the Time Delay Express VI to account for

the settling time of the SCXI-1104/C.

9. Acquire 1000 points of voltage data using the Analog 1D DBL 1Chan

NSamp instance of the DAQmx Read VI.

10. Compute the mean of the 1000 voltage values that you acquired.

11. Compare the resulting average to the upper and lower limits listed in

Table 3. If the result is between the upper and lower limits, the

SCXI-1104/C passes the test.

12. Clear the acquisition using the DAQmx Clear Task VI.

LabVIEW Block Diagram Function Call

Call a sleep or wait function to suspend

execution for 350 ms.

LabVIEW Block Diagram NI-DAQmx Function Call

Call DAQmxReadAnalogF64 with the following

parameters:

taskHandle: taskHandle

numSampsPerChan: –1

timeout: 10.0

fillMode: DAQmx_Val_GroupByChannel

readArray: data

arraySizeInSamples: 1000

sampsPerChanRead: &read

reserved: NULL

LabVIEW Block Diagram NI-DAQmx Function Call

Call DAQmxClearTask with

the following parameter:

taskHandle: taskHandle

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