National Instruments NI 5922 Manual

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
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
No
Adjust (Cal Dates and
Temperatures Updated)
Adjust
Anyway?
No
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