National Instruments 9235, 9236 Calibration Procedure

NI 9235/9236 Calibration Procedure

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This document contains information about calibrating National Instruments 9235/9236 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.

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

Connecting the Calibrator to the Module ........................................ 6

Verification Procedures ................................................................... 8

Measurement Accuracy Verification........................................8

Shunt Calibration Accuracy Verification ................................. 12

Excitation Voltage Verification ................................................ 16

Specifications ..........................................................................................17

Test Limits .............................................................................................. 18

Calibrator Output ............................................................................. 18

Nominal Value.................................................................................18

1-Year Limits...................................................................................18

Where to Go for Support......................................................................... 20

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

Software

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

installing the NI 9235/9236. NI-DAQmx, available at and controls the NI 9235/9236.

Italic text in this font denotes text that is a placeholder for a word or value that you must supply.

Install NI-DAQmx 8.8 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.

ni.com/downloads, configures

NI-DAQmx supports a number of programming languages, including LabVIEW, LabWindows Visual Basic 6.0, Microsoft .NET, and Borland C++.

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

Program Files\National Instruments\NI-DAQ\Examples

directory.

™

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

NIDAQmx.h, like any standard

NI 9235/9236 Calibration Procedure 2 ni.com

Documentation

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

latest versions from the NI Web site at

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 guides 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.

ni.com/manuals.

• NI 9235/9236 Operating Instructions and Specifications—This

document describes how to use the NI 9235/9236 and includes specifications and terminal assignments for the NI 9235/9236. The limits you use to verify the accuracy of the devices are based on the specifications found in this document. You can download the latest version of this document from the NI Web site at

ni.com/manuals.

Calibration Interval

The NI 9235/9236 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.

Test Equipment

National Instruments recommends that you use the following equipment for calibrating the NI 9235/9236.

Table 1. Recommended Equipment

Equipment Recommended Model Requirements

Calibrator Fluke 5500A If this instrument is unavailable, use a calibrator with

generation of resistances in the ranges of 108 Ω – 132 Ω and 315 Ω –385Ω with 0.01 Ω resolution, an accuracy of at least 90 ppm, and automatic lead wire compensation.

DMM NI 4070 If this instrument is unavailable, use a multi-ranging

6 1/2 digit DMM with an accuracy of at least 40 ppm.

Chassis NI cDAQ chassis —

Connecting wires

Test Conditions

— Connections between the module and the calibrator are

insensitive to connection resistance except between the calibrator LO terminal and the module RC terminal. The resistance of this connection must be less than 200 mΩ to limit bridge linearity errors. The verification test limits in Tables 5 and 6 assume this requirement is met.

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 ±5 °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.

NI 9235/9236 Calibration Procedure 4 ni.com

Calibration Procedure

This section provides instructions for verifying the performance of the NI 9235/9236.

Calibration Process Overview

The calibration process consists of the following steps:

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

2. Verification Procedures—Verify the existing operation of the device. This step confirms whether the device is operating within its specified range and whether it needs adjustment.

3. Adjustment—If the device does not fall within the desired specifications, submit the device to NI for a factory calibration to adjust the calibration constants.

4. Verification Procedures—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 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.

Connecting the Calibrator to the Module

Complete the following steps to connect the calibrator to the module for both the measurement accuracy verification and the shunt calibration verification:

1. Set the calibrator to standby mode (STBY).

2. Connect the AUX LO terminal of the calibrator to the LO terminal of the calibrator.

3. Using discrete connections, connect the LO terminal of the calibrator to the AI and RC terminals of the module channel you want to verify. Leave all other channels unconnected.

Note The three connections to the calibrator LO terminal must be connected at the

calibrator output jack.

Note Ensure that the connection resistance between the calibrator LO terminal and the

module RC terminal meets the requirement listed in Table 1.

4. Connect the HI terminal of the calibrator to the EXC0 terminal of the module.

5. Connect the AUX HI terminal of the calibrator to the EXC1 terminal of the module.

Note You do not have to change the EXC terminal connections for each channel you

verify, because the EXC terminals all connect to a common excitation supply inside the NI 9235/9236.

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