National Instruments 9205 Manuale

NI 9205/9206 Calibration

Procedure

This document contains information about calibrating National

Instruments 9205/9206 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.

The NI 9205 and NI 9206 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 two years. You can shorten this interval based

on the accuracy demands of your application or requirements of your

processes. Self-calibration can be performed as needed or when the

temperature varies by 5 °C or more from the last external calibration.

Contents

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

Calibration Options ................................................................................. 3

Self-Calibration................................................................................ 3

External Calibration ......................................................................... 3

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

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

Documentation................................................................................. 4

Calibration Requirements ....................................................................... 5

Password .......................................................................................... 5

Test Equipment ................................................................................ 5

Test Conditions ................................................................................ 5

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

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

Initial Setup...................................................................................... 6

Self-Calibration................................................................................ 6

NI 9205/9206 Calibration Procedure 2 ni.com

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

Adjustment Procedure ......................................................................10

AI Absolute Accuracy Tables and Formulas...........................................12

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

Using the Table.................................................................................13

Range.........................................................................................13

Test Point...................................................................................14

2-Year Limits ............................................................................14

Where to Go for Support .........................................................................15

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.

NI 9205/9206 NI 9205/9206 refers to the NI 9205 and NI 9206.

©National Instruments Corporation 3 NI 9205/9206 Calibration Procedure

Calibration Options

The NI 9205/9206 support two types of calibration: self-calibration and

external calibration.

Self-Calibration

Self-calibration, also known as internal calibration, uses a software

command and requires no external connections. Self-calibration improves

measurement accuracy by compensating for variables such as temperature

that might have changed since the last external calibration. Self-calibration

retains the traceability of the external calibration and can be performed as

necessary to compensate for environmental changes.

External Calibration

External calibration is generally performed with a high-precision calibrator

at either NI or a metrology lab. This procedure replaces all calibration

constants in the EEPROM and is equivalent to a factory calibration at NI.

Because the external calibration procedure changes all EEPROM

constants, it invalidates the original calibration certificate. If an external

calibration is done with a traceable signal generator source, a new

calibration certificate can be issued. This document describes specific

programming steps for writing an external calibration procedure for the

NI 9205/9206.

Software and Documentation Requirements

This section describes the software and documentation required for both

self-calibration and external calibration.

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 9205/9206. NI-DAQmx, available at ni.com/downloads, configures

and controls the NI 9205/9206.

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++.

NI 9205/9206 Calibration Procedure 4 ni.com

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

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 9205 Operating Instructions/NI 9206 Operating Instructions—

These documents contain information about specific device features.

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

versions of these documents from the NI Web site at ni.com/

manuals.

©National Instruments Corporation 5 NI 9205/9206 Calibration Procedure

Calibration Requirements

Password

The default password for password-protected operations is NI.

Test Equipment

National Instruments recommends that you use the following equipment

for calibrating the NI 9205/9206:

• Fluke 5700A calibrator. If that instrument is unavailable, use a

high-precision voltage source with an accuracy of at least 10 ppm.

• NI cDAQ-9172 chassis.

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.

Calibration Process

This section provides instructions for verifying and adjusting the

NI 9205/9206.

Calibration Process Overview

The calibration process consists of the following steps:

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

2. Self-Calibration—Measure the onboard reference voltage of the

device and adjust the self-calibration constants.

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

This step confirms whether the device was operating within its

specified range prior to calibration.

NI 9205/9206 Calibration Procedure 6 ni.com

4. Adjustment Procedure—Perform an external calibration that adjusts

the device calibration constants with respect to a known voltage

source.

5. Perform another verification to ensure that the device operates within

its specifications after adjustment.

The first four 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.

Self-Calibration

Self-calibrate the device before completing the first verification, after the

device has warmed up for the recommended time period. DAQmxSelfCal

(DAQmx Self Calibrate VI), as shown in the following table, measures the

onboard reference voltage of the device and adjusts the self-calibration

constants to account for any errors caused by short-term fluctuations in the

operating environment. When you self-calibrate a device, no external

signal connections are necessary.

NI-DAQmx Function Call LabVIEW Block Diagram

Call DAQmxSelfCal with the

following parameters:

deviceName: dev1

©National Instruments Corporation 7 NI 9205/9206 Calibration Procedure

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 Device 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

prior to calibration. Because the NI 9205/9206 has many different ranges,

you must verify measurements for each available range on these modules.

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

1. Refer to Table 1 for a list of the NI connection accessories for the

NI 9205/9206 and instructions on connecting the calibrator to the

device.

2. Set the calibrator voltage to the Test Point 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.

Table 1. NI Connection Accessories

Device Connection Accessory Connection Instructions

NI 9205/9206 NI 9940 36-position strain

relief & high voltage connector

kit

Connect the positive output of the calibrator to

AI0 (pin 1) and the negative output of the

calibrator to AI8 (pin 19) and COM (pin 17). If

the calibrator has a guard connection, connect

that terminal to COM instead of connecting

COM to the negative output.

NI 9205 with

DSUB

NI 9933 37-pin connector kit,

screw terminal connector and

DSUB shell

Connect the positive output of the calibrator to

AI0 (pin 1) and the negative output of the

calibrator to AI8 (pin 20) and COM (pin 10). If

the calibrator has a guard connection, connect

that terminal to COM instead of connecting

COM to the negative output.

NI-DAQmx Function Call LabVIEW Block Diagram

Call DAQmxCreateTask with the

following parameters:

taskName:

AIVerificationTask

taskHandle: &taskHandle

LabVIEW does not require this step.

NI 9205/9206 Calibration Procedure 8 ni.com

4. Create and configure an AI voltage channel through NI-DAQmx using

DAQmxCreateAIVoltageChan (DAQmx Create Virtual Channel

VI), as shown in the following table. Use Table 4 to determine the

minimum and maximum values for the device.

5. Configure the timing properties for the voltage acquisition using

DAQmxCfgSampClkTiming (DAQmx Timing VI), as shown in the

following table.

NI-DAQmx Function Call LabVIEW Block Diagram

Call DAQmxCreateAIVoltageChan

with the following parameters:

taskHandle: taskHandle

physicalChannel: dev1/ai0

nameToAssignToChannel:

myVoltageChannel

terminalConfig:

DAQmx_Val_Cfg_Default

minVal:

–10.0

maxVal:

10.0

units: DAQmx_Val_Volts

customScaleName: NULL

NI-DAQmx Function Call LabVIEW Block Diagram

Call DAQmxCfgSampClkTiming

with the following parameters:

taskHandle: taskHandle

source: NULL

rate: 100000.0

activeEdge:

DAQmx_Val_Rising

sampleMode:

DAQmx_Val_FiniteSamps

sampsPerChan: 10000

©National Instruments Corporation 9 NI 9205/9206 Calibration Procedure

6. Start the acquisition using DAQmxStartTask (DAQmx Start Task VI),

as shown in the following table.

7. Acquire 10,000 points of voltage data using DAQmxReadAnalogF64

(DAQmx Read VI), as shown in the following table.

8. Average the voltage values that you acquired. Compare the resulting

average to the Upper Limit and Lower Limit values in Table 4. If the

result is between these values, the device passes the test.

9. Clear the acquisition using DAQmxClearTask (DAQmx Clear Task

VI), as shown in the following table.

10. Repeat steps 3 through 9 for all ranges and all values.

11. Disconnect the calibrator from the device or proceed to the Adjustment

Procedure section to adjust the analog input calibration constants.

NI-DAQmx Function Call LabVIEW Block Diagram

Call DAQmxStartTask with

the following parameter:

taskHandle: taskHandle

NI-DAQmx Function Call LabVIEW Block Diagram

Call DAQmxReadAnalogF64 with the

following parameters:

taskHandle: taskHandle

numSampsPerChan: –1

timeout: 10.0

fillMode:

DAQmx_Val_GroupByChannel

readArray: data

arraySizeInSamples: 10000

sampsPerChanRead: &read

reserved: NULL

NI-DAQmx Function Call LabVIEW Block Diagram

Call DAQmxClearTask with the following

parameter:

taskHandle: taskHandle

NI 9205/9206 Calibration Procedure 10 ni.com

Adjustment Procedure

The NI 9205/9206 adjustment procedure adjusts the analog input

calibration constants. At the end of each adjustment procedure, the new

constants are stored in the external calibration area of the device EEPROM.

These values are password-protected, which ensures that you do not

accidentally access or modify any calibration constants adjusted by the

metrology laboratory. The default password is NI.

Complete the following steps to adjust the device with a calibrator:

1. Refer to Table 1 for a list of the NI connection accessories for the

NI 9205/9206 and instructions on connecting the calibrator to the

device.

2. Set the calibrator to output 4.0 V.

3. Open a calibration session on the device using DAQmxInitExtCal

(DAQmx Initialize External Calibration VI), as shown in the following

table.

NI-DAQmx Function Call LabVIEW Block Diagram

Call DAQmxInitExtCal

with the following

parameters:

deviceName: dev1

password: NI

calHandle: &calHandle

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