National Instruments NI PXI-4070 Bedienungsanleitung

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May 2003

370532B-01

NI PXI-4070 6½ Digit FlexDMM

Calibration Procedure

This document contains step-by-step instructions for writing an external

calibration procedure for the NI PXI-4070 6½ digit FlexDMM and

1.8 MS/s isolated digitizer (NI 4070).

Contents

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

Calibration Overview.............................................................................. 3

What Is Calibration? ........................................................................ 3

Why Should You Calibrate? ............................................................ 3

How Often Should You Calibrate? .................................................. 4

What Calibration Options Are Available?....................................... 4

How Much Time Does Calibration Require? .................................. 4

Equipment and Other Test Requirements ............................................... 5

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

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

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

Documentation................................................................................. 6

Software ........................................................................................... 7

Verification Procedures........................................................................... 10

Setting Up the Test Equipment........................................................ 10

Verifying DC Voltage...................................................................... 11

Verifying AC Voltage...................................................................... 19

Verifying 4-Wire Resistance ........................................................... 27

Verifying 2-Wire Resistance ........................................................... 29

Verifying DC Current ...................................................................... 34

Verifying AC Current ...................................................................... 36

Verifying Frequency ........................................................................ 38

Adjustment Procedures ........................................................................... 40

Setting Up the Test Equipment........................................................ 40

Adjusting DC Voltage and Resistance............................................. 41

Adjusting AC Voltage (AC- and DC-Coupled) Modes................... 47

™

ni.com

NI PXI-4070 Calibration Procedure 2 ni.com

Adjusting Current Modes .................................................................54

Completing the Adjustment Procedures...........................................57

Verification Limits ..................................................................................58

DC Voltage.......................................................................................58

AC Voltage.......................................................................................58

4-Wire Resistance.............................................................................60

2-Wire Resistance.............................................................................61

DC Current .......................................................................................62

AC Current .......................................................................................62

Frequency .........................................................................................63

Calibration Function Reference...............................................................63

Technical Support Resources ..................................................................63

NI Web Support................................................................................63

Worldwide Support ..........................................................................64

Conventions

The following conventions are used 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.

This icon denotes a caution, which advises you of precautions to take to

avoid injury, data loss, or a system crash.

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, hardware labels,

or an introduction to a key concept. This font 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, and code excerpts.

©National Instruments Corporation 3 NI PXI-4070 Calibration Procedure

Calibration Overview

The complete calibration process for the NI 4070 consists of verifying

all modes with the test limits provided and adjusting the calibration

coefficients for all modes. Frequency is the only mode that does not require

adjustment. Reverifying all modes after adjustments ensures that the

adjustment procedures were performed correctly.

National Instruments can perform stringent in-house calibration of the

NI 4070 and can generate either a basic or a detailed calibration certificate

for you. Visit ni.com/calibration for more information on calibration

certificates. This document is provided for those who wish to perform the

calibration procedure themselves.

What Is Calibration?

Calibration is a set of operations that compares the values indicated by a

measuring instrument or measuring system to the corresponding values

realized by external standards. The result of a calibration can be used to

determine the measurement error and can correct for it in the adjustment

process.

The calibration process consists of verifying, adjusting, and reverifying a

device. During verification, you compare the measured performance to an

external standard of known measurement uncertainty to confirm that the

product meets or exceeds specifications. During adjustment, you correct

the measurement error of the device by adjusting the calibration constants

and storing the new calibration constants in the EEPROM.

Normally, the calibration sequence is as follows:

1. Verify the NI 4070 using the 2-year accuracy limits (or the 90-day

accuracy limits if it has been externally calibrated within that time).

2. Adjust the NI 4070.

3. Reverify the NI 4070 using the 24-hour accuracy limits (or the 2-year

accuracy limits when the 24-hour limits are not specified).

Why Should You Calibrate?

Properties of the electrical components responsible for gain and offset

errors may drift with time, temperature, and mechanical stress. Calibration

is required to compensate for this drift and ensure that you, as a user, are

confident that any measurements you make meet NI 4070 specifications.

NI PXI-4070 Calibration Procedure 4 ni.com

How Often Should You Calibrate?

The accuracy requirements of your measurement application determine

how often you should calibrate the NI 4070. NI recommends performing a

complete calibration at least once every two years. NI does not guarantee

the absolute accuracy of the NI 4070 beyond this two year calibration

interval. You can shorten the calibration interval based on the demands

of your application.

What Calibration Options Are Available?

Depending on your measurement and accuracy requirements, a complete

calibration of the NI 4070 may not be necessary. A number of options are

available that can shorten the time you spend on the calibration. The

following options are available:

• Complete calibration—Performing the entire calibration procedure

from beginning to end is the only way to guarantee that the

performance of the NI 4070 will meet or exceed the published

specifications for all modes and ranges.

• Complete calibration except AC voltage modes—If you do not use the

AC voltage modes for any measurements or the accuracy is irrelevant,

you have the option to skip these steps in the calibration procedure.

• Complete calibration except current modes—If you do not use the

current modes (neither DC nor AC) or the accuracy is insignificant for

your application, you have the option to skip the steps to calibrate both

current modes.

• Complete calibration except AC voltage and current modes—You can

choose to skip both the AC voltage modes calibration and the current

modes calibration if your application does not require them or the

accuracy is irrelevant.

How Much Time Does Calibration Require?

The amount of time required for calibrating varies depending on whether

you are running in automated mode or in manual mode. In automated

mode, the complete verification procedures for the NI 4070 take less than

30 minutes, and the complete adjustment procedures take approximately

50 minutes. If you choose to run the calibration in manual mode,

the process requires more time and is more prone to operator error.

NI recommends using an automated procedure, such as the procedures

available with National Instruments Calibration Executive software.

For more information on calibration, visit ni.com/calibration.

©National Instruments Corporation 5 NI PXI-4070 Calibration Procedure

Equipment and Other Test Requirements

This section describes the equipment, test conditions, documentation,

software, and connections required for calibration.

Required Test Equipment

The following equipment is required for calibrating the NI 4070:

• Fluke 5700A multifunction calibrator calibrated within the last

90 days or a Fluke 5720A multifunction calibrator calibrated within

the last year

• Pomona 5145 insulated double banana plug shorting bar (or another

means of creating a short with low thermal EMF (≤150 nV) across the

HI and LO input banana connectors on the NI 4070)

• Two Pomona B-4 banana-to-banana patch cords (cables) or similar

banana-to-banana cables with length not to exceed 4 in.

•Wire(≤22 AWG, ≤4 in.) for connecting the AUX CURRENT and

SENSE HI binding posts of the calibrator (alternatively, you can use

one of the Pomona B-4 cables instead of this wire)

• National Instruments PXI chassis and controller

• National Instruments calibration cable assembly for the NI 4070

(part number 161283A-01)

Optional Test Equipment

The following equipment is optional for calibrating the NI 4070 and is only

used for frequency verification:

• NI PXI-6608

• National Instruments SH68-68-D1 shielded cable

• National Instruments TB-2715 terminal block

• Pomona MDP 4892 double banana plug with strain relief

• Coaxial cable (for example, RG178)

Test Conditions

Follow these guidelines to optimize the connections and the environment

during calibration:

• Ensure that the PXI chassis fan speed is set to HI and that the fan filters

are clean.

• Plug the PXI chassis and the calibrator into the same power strip to

avoid ground loops.

NI PXI-4070 Calibration Procedure 6 ni.com

• Power on and warm up both the calibrator and the NI 4070 for at least

30 minutes before beginning this calibration procedure.

• Maintain an ambient temperature of 23 ±1 °C.

• Maintain an ambient relative humidity of less than 60%.

• Allow the calibrator to settle fully before taking any measurements.

Consult the Fluke 5700A/5720A user documentation for instructions.

• Allow the thermal EMF enough time to stabilize when you change

connections to the calibrator or the NI 4070. The suggested time

periods are stated where necessary throughout this document.

• Keep a shorting bar connected between the V GUARD and

GROUND binding posts of the calibrator at all times.

• Clean any oxidation from the spade lugs on the calibration cable

assembly before connecting them to the calibrator’s binding posts.

Oxidation is a discoloration that tarnishes the copper spade lugs so that

they appear dull rather than shiny.

• Leave the spade lugs on the calibration cable assembly that are labeled

SHD connected to the calibrator’s V GUARD binding post at all times.

• Prevent the cables from moving or vibrating by taping or strapping

them to a nonvibrating surface. Movement or vibration causes

triboelectric effects that can result in measurement errors.

Documentation

In addition to this calibration document, you may find the following

references helpful in writing your calibration utility:

•NI Digital Multimeters Help

•NI-DMM Instrument Driver Quick Reference Guide

•NI Digital Multimeters Getting Started Guide

•Specifications for the NI PXI-4070

All of these documents are installed on your computer when you install

NI-DMM. To locate them, select Start»Programs»National

Instruments»NI-DMM»Documentation.

If you are performing the optional frequency verification procedure,

you may need the following documents, which are available at ni.com/

manuals:

•TB-2715 Terminal Block Installation Guide

•About Your NI 6608 Device

©National Instruments Corporation 7 NI PXI-4070 Calibration Procedure

Software

The NI 4070 calibration procedure requires that NI-DMM version 2.1 or

later be installed on the calibration system. NI-DMM supports a number of

programming languages including LabVIEW, LabWindows™/CVI™,

Microsoft Visual C++, and Microsoft Visual Basic. When you install

NI-DMM, you only need to install support for the language you intend to

use to write your calibration utility.

Note NI-DMM versions earlier than version 2.1 do not support NI 4070 calibration.

The procedures in this document are described using C function calls.

You also can program in LabVIEW using the VIs that correspond to the

C function calls. Figure 1 shows the procedural flow for verification.

Figure 2 shows the procedural flow for adjustment.

NI PXI-4070 Calibration Procedure 8 ni.com

Figure 1. Verification Procedures Flowchart

Verify

DC Voltage

Modes?

Verify

4-Wire Resistance

Modes?

Verify

AC Voltage

Modes?

Verify

2-Wire Resistance

Modes?

Verify

DC Current

Modes?

Verify

AC Current

Modes?

Verify

Frequency

Mode?

Setting up

the Test

Equipment

Go to

Verifying

DC Voltage

Go to

Verifying

AC Voltage

Go to

Verifying

4-Wire Resistance

Go to

Verifying

2-Wire Resistance

Go to

Verifying

DC Current

Go to

Verifying

AC Current

Go to

Verifying

Frequency

Ye s

Go to

Adjustment

Procedures

Flowchart

Completing the

Adjustment

Procedures

Pre-Adjustment Post-Adjustment

Is this a

Pre-Adjustment or

Post-Adjustment

Verification?

©National Instruments Corporation 9 NI PXI-4070 Calibration Procedure

Figure 2. Adjustment Procedures Flowchart

Ye s Go to

Verification

Procedures Flowchart

Verification

Go to

Adjusting

DC Voltage and

Resistance

Go to

Adjusting

AC Voltage Modes

Ye s

Completing the

Adjustment

Procedures

Adjust

AC Voltage

Modes?

Adjust

Current

Modes?

Go to

Adjusting

Current Modes

Perform

Post-Adjustment

Verification?

NI PXI-4070 Calibration Procedure 10 ni.com

Verification Procedures

You can use the verification procedures described in this section for both

pre-adjustment and post-adjustment verification. The steps of each

verification procedure must be performed in the order listed; however, you

can omit entire sections (for example, the entire Verifying AC Current

section), if necessary.

The parameters Range, Resolution, and Sample Interval used in function

calls throughout this section have floating point values. For example, if

Range = 1, the floating point value is 1.0. The parameters Trigger Count,

Sample Count, Array Size, and ParamValue have integer values. Refer

to the NI Digital Multimeters Help for more information.

Note Many of the parameter values listed in this document are expressed in scientific

notation. Some programming languages do not support the direct entry of numbers in this

format. Care must be taken to properly enter these values with the appropriate number of

zeros. For example, the scientific notation number 10e–6 must be entered as 0.00001, and

the number 100e3 must be entered as 100000. If your programming language supports

numeric entries in scientific notation, NI recommends that you use this feature to minimize

possible data entry errors.

Setting Up the Test Equipment

NoteThe Setting Up the Test Equipment section is necessary for pre-adjustment

verifications only. If you are performing a post-adjustment verification, skip the setup and

go directly to the Verifying DC Voltage section.

To set up the test equipment, complete the following steps:

1. Remove all connections from the four input banana connectors on the

NI 4070.

2. Verify that the calibrator has been calibrated within the time limits

specified in the Required Test Equipment section, and that DC zeros

calibration has been performed within the last 30 days. Consult the

Fluke 5700A/5720A user documentation for instructions on

calibrating these devices.

Note Ensure that both the calibrator and the NI 4070 (installed in a powered-on PXI

chassis) are warmed up for at least 30 minutes before you begin this procedure.

3. Call niDMM_init with the resource name of the device to create a

Session.

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