National Instruments 9237 Manuale

NI 9237 Calibration Procedure

This document contains information about calibrating National

Instruments 9237 modules using NI-DAQmx. This calibration procedure is

intended for metrology labs.

This document does not discuss programming techniques or compiler

configuration. The NI-DAQmx driver contains online help files that have

compiler-specific instructions and detailed function explanations. You can

install these help files when you install NI-DAQmx on the calibration

computer.

Contents

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

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

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

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

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

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

Calibration Procedure ............................................................................. 5

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

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

Verification Procedure ..................................................................... 6

Specifications .......................................................................................... 12

Test Limits .............................................................................................. 12

Using the Table................................................................................ 12

Excitation Setting Value........................................................... 12

Calibrator Output ...................................................................... 12

Range ........................................................................................ 12

Test Point Value ....................................................................... 13

1-Year Absolute Error .............................................................. 13

Where to Go for Support......................................................................... 14

NI 9237 Calibration Procedure 2 ni.com

Conventions

The following conventions appear in this manual:

»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 and hardware labels.

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 Monospace text 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

Install NI-DAQmx 8.1 or later on the calibration computer. NI-DAQmx

includes high-level function calls to simplify the task of writing software to

calibrate devices. You must have the proper device driver installed on the

calibration system before calibrating the device.

Note NI recommends that you install the NI-DAQmx driver software before physically

installing the NI 9237. NI-DAQmx, available at ni.com/downloads, configures and

controls the NI 9237.

NI-DAQmx supports a number of programming languages, including

LabVIEW, LabWindows™/CVI™, Microsoft Visual C++ 6.0, Microsoft

Visual Basic 6.0, Microsoft .NET, and Borland C++.

You can access the NI-DAQmx header file, NIDAQmx.h, like any standard

library. You can find examples of how to use the NI-DAQmx driver in the

©National Instruments Corporation 3 NI 9237 Calibration Procedure

Program Files\National Instruments\NI-DAQ\Examples

directory.

Documentation

You might find the following documentation helpful as you write the

calibration procedure:

•NI-DAQmx Help—This help file contains general information about

measurement concepts, key NI-DAQmx concepts, and common

applications that apply to all programming environments. To access

this help file, select Start»All Programs»National Instruments»

NI-DAQ»NI-DAQmx Help.

•NI-DAQmx C Reference Help—This help file contains C reference and

general information about measurement concepts. To access this help

file, select Start»All Programs»National Instruments»NI-DAQ»

NI-DAQmx C Reference Help.

•DAQ Getting Started Guide for NI-DAQ 8.0 or later—This guide

describes how to install NI-DAQmx for Windows software and

NI-DAQmx-supported DAQ devices, and how to confirm that your

device is operating properly. To access this guide, select Start»

All Programs»National Instruments»NI-DAQ»DAQ Getting

Started Guide.

Note The documents above are installed with NI-DAQmx. You can also download the

latest versions from the NI Web site at ni.com/manuals.

•NI 9237 Operating Instructions—This document describes how to use

the NI 9237 and includes specifications and terminal assignments for

the NI 9237. You can download the latest version of this document

from the NI Web site at ni.com/manuals.

Calibration Interval

The NI 9237 should be calibrated at a regular interval as defined by

the measurement accuracy requirements of your application. National

Instruments recommends that you routinely perform a complete calibration

at least once every year. You can shorten this interval based on the accuracy

demands of your application or requirements of your processes. Adjusting

the calibration constants must be done by a factory calibration at NI.

NI 9237 Calibration Procedure 4 ni.com

Test Equipment

National Instruments recommends that you use the following equipment

for calibrating the NI 9237.

Test Conditions

Follow these guidelines to optimize the connections and the environment:

• Keep connections to the device as short as possible. Long cables and

wires act as antennae, picking up extra noise 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 an ambient temperature of 23 ±10 °C. The device

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

measurement circuitry is at a stable operating temperature.

Table 1. Recommended Equipment

Equipment Recommended Model Requirements

Calibrator Fluke 5700A If this instrument is unavailable, use a

high-precision voltage source with an

accuracy of at least 10 ppm and an

output impedance of less than or equal

to 50 Ω.

DMM NI 4070 DMM If this instrument is unavailable, use a

multiranging 6 ½ digit DMM with an

accuracy of at least 40 ppm.

Chassis NI cDAQ-9172 —

Connection accessories RJ-50, RJ-50 cable Use an RJ-50 10-position connector

plug and an RJ-50 cable.

Bridge completion

accessories

NI 9949, 350 Ωresistors Use one NI 9949 screw terminal

accessory and two 350 Ωresistors with

at least 1% tolerance.

©National Instruments Corporation 5 NI 9237 Calibration Procedure

Calibration Procedure

This section provides instructions for verifying the performance of the

NI 9237.

Calibration Process Overview

The calibration process consists of the following steps:

1. Initial Setup—Configure the device in NI-DAQmx.

2. Verification Procedure—Verify the existing operation of the device.

This step confirms whether the device was operating within its

specified range prior to calibration.

3. Adjustment—Submit the device to NI for a factory calibration to adjust

the calibration constants.

4. Verification Procedure—Perform another verification to ensure that

the device operates within its specifications after adjustment.

The first two steps are explained in the following sections.

Initial Setup

You must configure the device in Measurement & Automation Explorer

(MAX) to communicate with NI-DAQmx.

Complete the following steps to configure a device in MAX.

1. Install the NI-DAQmx driver software.

2. Make sure that no power is connected to the module terminals. If the

system is in a nonhazardous location, the chassis power can be on

when you install the module.

3. Insert the module into an available slot in the cDAQ-9172 chassis.

4. Launch MAX.

5. Right-click the device name and select Self-Test to ensure that the

device is working properly.

Note When a device is configured with MAX, it is assigned a device name. Each function

call uses this device name to determine which DAQ device to calibrate. This document uses

dev1 to refer to the device name. In the following procedures, use the device name as it

appears in MAX.

NI 9237 Calibration Procedure 6 ni.com

Verification Procedure

Verification determines how well the device is meeting its specifications.

By completing this procedure, you can see how the device has drifted over

time, which helps you determine the appropriate calibration interval for

your application. Table 4 in the Test Limits section shows all acceptable

settings for the device type. Throughout the verification process, use

Table 4 to determine if the device is operating within its specified range.

You must perform verification on all analog input channels.

Complete the following steps to test the performance of the device.

1. Make the following connections on the NI 9949 terminal block:

• Insert one leg of each 350 Ωresistor into AI–.

• Insert the second leg of one 350 Ωresistor into EX+.

• Insert the second leg of the other 350 Ωresistor into EX–.

• Connect RS+ to EX+.

• Connect RS– to EX–.

• Connect the positive input of the DMM to RS+.

• Connect the negative input of the DMM to RS–.

• Connect the positive output of the calibrator to AI+.

• Connect the negative output of the calibrator to AI–.

• Leave the SC, T+, and T– terminals unconnected.

• If the calibrator has a separate guard connection not connected to

LO, connect that terminal to AI–.

Refer to Table 2 for the pin assignments and signal names of the NI 9237.

Refer to Figure 1 for an illustration of the NI 9949 connections.

©National Instruments Corporation 7 NI 9237 Calibration Procedure

Figure 1. NI 9949 Connections

Table 2. Pin Assignments and Signal Names

Module RJ-50 Pin Signal Name Signal Description

1SC Shunt calibration

2AI+ Positive analog input

3AI– Negative analog input

4RS+ Positive remote sense input

5RS– Negative remote sense input

6EX+ Positive excitation output*

7EX– Negative excitation output*

8T+ TEDS DATA

9T– TEDS Return*

10 SC Shunt calibration

* These signals are shared by all four RJ-50 connectors on the NI 9237.

–+

–

EX+

RS+

RS–

EX–

DMM

AI–

Calibrator

Guard

AI+

NI 9237 Calibration Procedure 8 ni.com

2. Set the calibrator voltage to the Calibrator Output value indicated in

Table 4. NI recommends that you verify all values, although you can

save time by verifying only the values used in your application.

3. If you use C function calls, create a task using DAQmxCreateTask, as

shown in the following table. If you use LabVIEW, skip this step. The

task is created in step 4 in LabVIEW.

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 Corporation 9 NI 9237 Calibration Procedure

4. Create and configure an AI Custom Voltage with Excitation channel

using the DAQmx Create Virtual Channel VI, as shown in the

following table. Use Table 4 to determine the minimum and maximum

values for the device.

Note Throughout the procedure, refer to the NI-DAQmx function parameters for the

LabVIEW input values.

LabVIEW Block Diagram NI-DAQmx Function Call

Call

DAQmxCreateAIVoltageChan

WithExcit with the following

parameters:

taskHandle: taskHandle

physicalChannel: dev1/ai0

nameToAssignToChannel:

myVoltageChannel

terminalConfig:

DAQmx_Val_Cfg_Default

minVal: –0.025

maxVal: 0.025

units: DAQmx_Val_Volts

bridgeConfig:

DAQmx_Val_FullBridge

voltageExcitSource:

DAQmx_Val_Internal

voltageExcitVal:*2.5, 3.3,

5.0, or 10.0

useExcitforScaling: TRUE

customScaleName: NULL

*Use the excitation value that corresponds to the calibrator voltage value you set in step 2. Refer to Table 4 for corresponding

excitation setting and calibrator output values.

NI 9237 Calibration Procedure 10 ni.com

5. Configure the timing properties for the voltage acquisition using the

DAQmx Timing VI, as shown in the following table.

6. Start the acquisition using the DAQmx Start Task VI, as shown in the

following table.

LabVIEW Block Diagram NI-DAQmx Function Call

Call DAQmxCfgSampClkTiming

with the following parameters:

taskHandle: taskHandle

source: NULL

rate: 50000

activeEdge:

DAQmx_Val_Rising

sampleMode:

DAQmx_Val_FiniteSamps

sampsPerChan: 10000

LabVIEW Block Diagram NI-DAQmx Function Call

Call DAQmxStartTask with the

following parameter:

taskHandle: taskHandle

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