National Instruments NI 5922 Manuale

CALIBRATION PROCEDURE

NI 5922

This document describes specific programming steps for writing

a calibration utility for the National Instruments PXI-5922

flexible-resolution digitizer. This calibration procedure is intended

for metrology labs.

Contents

Introduction............................................................................................. 2

Self-Calibration................................................................................ 2

External Calibration......................................................................... 2

Calibration Intervals ........................................................................ 2

Software and Documentation........................................................... 2

Self-Calibration Procedures .................................................................... 4

MAX ................................................................................................ 5

Scope SFP ........................................................................................ 5

NI-SCOPE ....................................................................................... 5

External Calibration Options .................................................................. 6

Complete Calibration....................................................................... 7

Optional Calibration ........................................................................ 8

External Calibration Requirements ......................................................... 10

Test Equipment ................................................................................ 10

Test Conditions ................................................................................ 10

External Calibration Procedures ............................................................. 11

Verifying NI 5922 Specifications .................................................... 11

Vertical Offset Accuracy .......................................................... 12

Noise......................................................................................... 13

Input Bias Current .................................................................... 15

Vertical Gain Accuracy ............................................................ 17

Timing Accuracy ...................................................................... 19

Flatness ..................................................................................... 20

Trigger Sensitivity .................................................................... 24

Adjusting the NI 5922...................................................................... 25

NI 5922 Calibration Procedure 2 ni.com

Calibration Utilities .................................................................................27

MAX.................................................................................................27

NI-SCOPE ........................................................................................27

Where to Go for Support .........................................................................28

Introduction

The NI 5922 supports two types of calibration: self-calibration (or internal

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 may have changed since the last external calibration. Self-calibration

retains the traceability of the external calibration.

External Calibration

External calibration is generally performed with a high-precision

oscilloscope calibrator at either NI or a metrology lab. The external

calibration 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.

Calibration Intervals

Self-calibration can be performed as necessary to compensate for

environmental changes.

Caution Although you can use self-calibration repeatedly, self-calibrating the NI 5922

more than a few times a day may cause excessive wear on the relays over time.

The measurement accuracy requirements of your application determine

how often you should externally calibrate the NI 5922. NI recommends

that you perform a complete external calibration at least once every

two years. You can shorten this interval based on the accuracy demands

of your application or the requirements of your processes. Refer to the

External Calibration Options section for more information.

©National Instruments Corporation 3 NI 5922 Calibration Procedure

Software and Documentation

Calibrating the NI 5922 requires installing NI-SCOPE version 2.8 or later

on the calibration system. You can download NI-SCOPE from

ni.com/downloads. NI-SCOPE supports programming the

self-calibration procedures in a number of programming languages.

However, only LabVIEW and C are supported for the external calibration

procedures.

NI-SCOPE 2.8 or later includes all the functions and attributes necessary

for calibrating the NI 5922. For LabWindows™/CVI™, the NI-SCOPE

function panel, niScopeCalfp, provides further help on the functions

available in CVI. LabVIEW support is installed in niScopeCal.llb, and

all calibration functions appear in the function palette. Refer to Table 1 for

file locations.

Calibration functions are C function calls or LabVIEW VIs in NI-SCOPE.

In this document, the C function call is shown first, followed by the

corresponding LabVIEW VI in parentheses. The C function calls are valid

for any compiler capable of calling a 32-bit DLL. Many of the functions use

constants defined in the niScopeCal.h file. To use these constants in C,

you must include niScopeCal.h in your code when you write the

calibration procedure.

For more information on the calibration functions and VIs, refer to the

NI-SCOPE Function Reference Help or the NI-SCOPE VI Reference Help.

These references can be found in the NI High-Speed Digitizers Help.

To access this help file, go to Start»Programs»National Instruments»

NI-SCOPE»Documentation»NI High-Speed Digitizers Help.

Table 1. Calibration File Locations after Installing NI-SCOPE 2.8 or Later

File Name and Location Description

IVI\Bin\niscope_32.dll NI-SCOPE driver containing the entire

NI-SCOPE API, including calibration functions

IVI\Lib\msc\niscope.lib NI-SCOPE library for Microsoft C containing

the entire NI-SCOPE API, including calibration

functions

LabVIEW (

version

)\examples\instr\

niScope

Directory of LabVIEW NI-SCOPE example

VIs, including self-calibration; access the

calibration example from the LabVIEW

function palette

NI 5922 Calibration Procedure 4 ni.com

You may find the following documentation helpful as you write your

calibration procedure:

• NI High-Speed Digitizers Getting Started Guide

• NI High-Speed Digitizers Help

• NI PXI-5922 Specifications

•NI-SCOPE Function Reference Help

• NI-SCOPE VI Reference Help

You can download the latest versions of all documentation from the NI Web

site at ni.com/manuals.

Self-Calibration Procedures

The NI 5922 includes precise internal circuits and references used during

self-calibration to adjust for time and temperature drift. The digitizer gain,

offset, and flatness are all corrected in self-calibration. Measuring the

accuracy of these internal calibration circuits with another instrument

during external calibration provides traceability for the verification

procedure. Absolute accuracy is ensured by compensating for any error

measured in the internal references.

Note Self-calibrate the digitizer before you perform verification. NI-SCOPE includes

self-calibration example programs for LabVIEW, CVI, and Microsoft Visual C.

LabVIEW (

version

)\instr.lib\niScope

Calibrate\niScopeCal.llb

LabVIEW VI library containing VIs for calling

the NI-SCOPE calibration API; access

calibration functions from the NI-SCOPE

calibration section of the LabVIEW function

palette

IVI\Drivers\niScope\niScopeCal.fp CVI function panel file that includes external

calibration function prototypes and help on

using NI-SCOPE in the CVI environment

IVI\Include\niScopeCal.h Calibration header file, which you must include

in any C program accessing calibration

functions. This file automatically includes

niScope.h, which defines the rest of the

NI-SCOPE interface

IVI\Drivers\niScope\Examples Directory of NI-SCOPE examples for CVI, C,

Visual C++, and Visual Basic

Table 1. Calibration File Locations after Installing NI-SCOPE 2.8 or Later (Continued)

File Name and Location Description

©National Instruments Corporation 5 NI 5922 Calibration Procedure

You can initiate self-calibration using Measurement & Automation

Explorer (MAX), using the Scope Soft Front Panel (SFP), or

programmatically using NI-SCOPE.

MAX

To initiate self-calibration from MAX, complete the following steps:

1. Disconnect or disable any AC inputs to the digitizer.

2. Launch MAX.

3. Select My System»Devices and Interfaces»NI-DAQmx Devices.

4. Select the device that you want to calibrate.

5. Initiate self-calibration using one of the following methods:

•ClickSelf-Calibrate in the upper right corner of MAX.

• Right-click the name of the device in the MAX configuration tree

and select Self-Calibrate from the drop-down menu.

Scope SFP

To initiate self-calibration from the Scope SFP, complete the following

steps:

1. Disconnect or disable any AC inputs to the digitizer.

2. Launch the Scope SFP by selecting Start»Programs»National

Instruments»NI-SCOPE»Scope Soft Front Panel.

3. Select the device you want to calibrate using the Device Configuration

dialog box by selecting Edit»Device Configuration.

4. Launch the Calibration dialog box by selecting Utility»

Self Calibration.

5. Click OK to begin self-calibration.

NI-SCOPE

To self-calibrate the NI 5922 programmatically using NI-SCOPE,

complete the following steps:

1. Disconnect or disable any AC inputs to the digitizer.

2. Call niScope_init (niScope Initialize VI) to obtain an instrument

session handle. Set the following parameters:

•resourceName: The device name assigned by MAX

•IDQuery: NISCOPE_VAL_VI_FALSE

•resetDevice: NISCOPE_VAL_VI_FALSE

•vi: The returned session handle that you use to identify the

instrument in all subsequent instrument driver function calls

NI 5922 Calibration Procedure 6 ni.com

3. Call niScope_CalSelfCalibrate (niScope Cal Self Calibrate VI)

with the following parameters:

•sessionHandle: The instrument handle that you obtain from

niScope_init (niScope Initialize VI)

•channelList: VI_NULL

•option: VI_NULL

Because the session is a standard session rather than an external

calibration session, the new calibration constants are immediately

stored in the EEPROM. Therefore, you can include this procedure in

any application that uses the digitizer.

4. Call niScope_close (niScope Close VI) to close the session handle.

Set the following parameter:

•vi: The instrument handle you obtained from niScope_init

External Calibration Options

External calibration involves both adjustment and verification. Adjustment

is the process of measuring and compensating for device performance to

improve the measurement accuracy. Performing an adjustment updates the

calibration date, effectively resetting the calibration interval. The device is

guaranteed to meet or exceed its published specifications for the duration

of the calibration interval. Verification is the process of testing the device

to ensure that the measurement accuracy is within certain specifications.

Verification can be used to ensure that the adjustment process was

successful or to determine if the adjustment process must be performed.

During verification, you must compare the measurement error to limits

given in Tables 3 through 8.

This document provides two sets of test limits for most verification

stages—the calibration test limits and the published specifications. The

calibration test limits are more restrictive than the published specifications.

If all of the measurement errors determined during verification fall within

the calibration test limits, the device is guaranteed to meet or exceed its

published specifications for a full calibration interval (two years). For this

reason, you must verify against the calibration test limits when performing

verification after adjustment. If all of the measurement errors determined

during verification fall within the published specifications, but not within

the calibration test limits, the device is meeting its published specifications.

However, the device will not necessarily remain within these specifications

for an additional two years. The device will meet published specifications

for the remainder of the current calibration interval. In this case, you can

perform an adjustment if you want to further improve the measurement

accuracy or reset the calibration interval. If some measurement errors

determined during verification do not fall within the published

©National Instruments Corporation 7 NI 5922 Calibration Procedure

specifications, you must perform an adjustment to restore the device

operation to its published specifications.

The Complete Calibration section describes the recommended calibration

procedure. The Optional Calibration section describes alternative

procedures that allow you to skip adjustment if the device already meets its

calibration test limits or published specifications.

Complete Calibration

Performing a complete calibration is the recommended way to guarantee

that the NI 5922 meets or exceeds its published specifications for a

two-year calibration interval. At the end of the complete calibration

procedure, you verify that the measurement error falls within the

calibration test limits. Figure 1 shows the programming flow for complete

calibration.

Figure 1. Complete Calibration Programming Flow

Adjust (Cal Dates and

Temperatures Updated)

Document

Post-Adjustment

Results

Document

Pre-Adjustment

Results

Calibration/

Verification

Complete

Ye s N o

Self-Calibrate

Verify

Meets

Calibration

Test Limits?

Review Verification/

Adjustment Procedure

or Return Device

NI 5922 Calibration Procedure 8 ni.com

Optional Calibration

You can choose to skip the adjustment steps of the calibration procedure if

the measurement error is within the calibration test limits or the published

specifications during the first verification. If all of the measurement errors

determined during the first verification fall within the calibration test

limits, the device is guaranteed to meet or exceed its published

specifications for a full calibration interval. In this case, you can update the

calibration date, effectively resetting the calibration interval, without

actually performing an adjustment. Refer to the Adjusting the NI 5922

section for more information.

If all of the measurement errors determined during the first verification fall

within the published specifications, but not within the calibration test

limits, adjustment is also optional. However, you cannot update the

calibration date because the device will not necessarily operate within the

published specifications for an additional two years.

Note Regardless of the results of the first verification, if you perform an adjustment, you

must verify that the measurement error falls within the calibration test limits at the end of

the calibration procedure.

©National Instruments Corporation 9 NI 5922 Calibration Procedure

Figure 2 shows the programming flow for the optional calibration.

Figure 2. Optional Calibration Programming Flow

Self-Calibrate

Verify

Meets

Calibration

Test Limits?

Ye s N o

Meets

Published

Specifications?

Ye s

Results

Within

Published Specs

(Adjustment

Optional)

Update Calibration

Dates and Temperatures

Without Adjusting

Adjust (Cal Dates and

Temperatures Updated)

Adjust

Anyway?

Calibration/

Verification

Complete

Ye s

Verify

Document

Post-Adjustment

Results

Document

Pre-Adjustment

Results

Meets

Calibration

Test Limits?

Review Verification/

Adjustment Procedure

or Return Device

NoYe s

NI 5922 Calibration Procedure 10 ni.com

External Calibration Requirements

Test Equipment

Table 2 lists the equipment required for externally calibrating the NI 5922.

If you do not have the recommended instruments, use these specifications

to select a substitute calibration standard.

Note The delay times indicated in this procedure apply specifically to the Fluke 9500B

calibrator. If you use a different calibrator, you may need to increase these delay times. This

increase varies between calibrator models.

Test Conditions

Follow these guidelines to optimize the connections and the environment

during calibration:

• Always connect the scope calibrator to the input BNC of the digitizer,

or use a short 50 ΩBNC coaxial cable if necessary. Long cables and

wires act as antennae, picking up extra noise that can affect

measurements.

• Keep relative humidity between 10 and 90% non-condensing.

• Maintain an ambient temperature of 23 ±5 °C.

Table 2. Required Equipment for NI 5922 External Calibration

Required Equipment

Recommended

Equipment

Parameter

Measured Specification

Signal Generator Fluke 9500B

oscilloscope

calibrator

9510 Test Head

(or Wavetek 9500

with high-stability

reference option)

Trigger Sensitivity ±3.5% absolute output

amplitude accuracy for

leveled sine wave up to

1 MHz into 1 MΩ

Timing 2 ppm frequency accuracy

Flatness 500 ps fall time pulse edge

aberrations:

< ±1.5% peak first 10 ns

< ±0.5% 10 ns to 1 µs

< ±0.1% peak beyond 1 µs

DC Source Fluke 5700 Vertical Gain DC ±50 ppm into 1 MΩ

BNC cable — — 50 Ω

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