National Instruments 446 Series Manual

NI 446XCalibration Procedure
This document contains information about calibrating National
Instruments PCI/PXI-4461 and PCI/PXI-4462 (NI 446X) devices.
This document does not discuss programming techniques or compiler
configuration. The National Instruments DAQmx driver includes 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.
NI 446X devices should be externally calibrated at a regular interval as
defined by the measurement accuracy requirements of your application.
NI recommends that you perform a complete calibration at least once every
year. Based on your measurement accuracy needs, you can shorten this
interval to 90 days or six months. 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
Password and User Information.............................................................. 5
Getting Calibration Information.............................................................. 6
Test Equipment ....................................................................................... 9
Test Conditions ....................................................................................... 9
Calibration Process ................................................................................. 10
Calibration Process Overview ......................................................... 10
Initial Setup...................................................................................... 10
Self-Calibration................................................................................ 11
NI 446XVerification Procedure ...................................................... 11
Verifying Analog Input Performance ....................................... 11
Verifying Analog Output Performance .................................... 19

NI 446X Calibration Procedure 2 ni.com
Verifying Timebase Frequency Accuracy.................................28
NI 446XAdjustment Procedure........................................................32
Adjusting the Analog Input .......................................................32
Adjusting the Analog Output ....................................................34
Adjusting the Timebase.............................................................40
Where to Go for Support .........................................................................42
Conventions
The following conventions appear in this document:
»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.
ReturnValue A parameter which points to data that is modified by a function call has a
variable name in the form <variableTypeReturnValue>, for example,
uInt32PointerReturnValue. All function calls return a status integer
that you must verify. Because all the functions return this status integer, the
function descriptions in this document omit the status integer.
Number Variable Types The integer variable type used in this document is represented as a whole
number. Any floating point variable type is represented as a number with a
decimal point. For example, the number 1,024 is written as 1024 if it is an
integer, and as 1024.0 if it is a floating point value.
NI 446XNI 446Xrefers to the NI PCI-4461, NI PXI-4461, NI PCI-4462, and
NI PXI-4462 unless otherwise noted.

©National Instruments Corporation 3 NI 446X Calibration Procedure
Calibration Options
NI 446Xdevices 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.
External Calibration
External calibration is generally performed with high-precision
instruments 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 traceable instruments, a new calibration
certificate can be issued.
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. 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 446Xdevice. NI-DAQmx, available at ni.com/downloads, configures
and controls the NI 446X.
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++.
If you want to write the calibration procedure using LabVIEW, NI
recommends that you use the Full or Professional Development System or
the Developer Suite Professional Edition. These editions include

NI 446X Calibration Procedure 4 ni.com
frequency-domain analysis tools not included in the Base Development
System.
You can access the NI-DAQmx header file, DAQmx.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 your
calibration procedure:
•NI-DAQmx Help—This help file contains general information about
measurement concepts, key NI-DAQmx concepts, and common
applications that are applicable to all programming environments.
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. Select
Start»All Programs»National Instruments»NI-DAQmx Base»
Documentation»C Function Reference Manual.
•DAQ Getting Started Guide for NI-DAQ 8.1 or later—This guide
describes how to install your NI-DAQmx for Windows software, your
NI-DAQmx-supported DAQ device, and how to confirm that your
device is operating properly. Select Start»All Programs»National
Instruments»NI-DAQ»DAQ Getting Started Guide.
•NI 446X Specifications—This document contains 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.
Select Start»All Programs»National Instruments» NI-DAQ»
Browse Device Documentation to launch the Device Documentation
Browser. You then can select the Dynamic Signal Acquisition book
to browse the list of DSA devices. Select your device to find a link to
the NI 446X Specifications.
These documents are installed with NI-DAQmx. You can also download
the latest versions from the NI Web site at ni.com/manuals.

©National Instruments Corporation 5 NI 446X Calibration Procedure
Password and User Information
For password-protected operations on most NI 446Xdevices, the default
password is NI. On certain devices, however, the default password is NI\0.
The password is stored in the device EEPROM. You can change the
password using the following NI-DAQmx function.
Note Depending on which programming language you use, you can write the \character
into a string several different ways. Refer to the standard of that language for information
about how to write the \character into a string.
You can write user-defined information into or read from the EEPROM
using the following NI-DAQmx functions.
NI-DAQmx Function Call LabVIEW Block Diagram
Call DAQmxChangeExtCalPassword
with the following parameters:
Device Name: dev1
Password: NI or NI\0
New Password: myNewPassword
(maximum four characters)
NI-DAQmx Function Call
Call DAQmxSetCalUserDefinedInfo with the following parameters:
deviceName: dev1
data: anyUserData
Call DAQmxGetCalUserDefinedInfoMaxSize with the following parameters:
deviceName: dev1
data: uInt32PointerReturnValue

NI 446X Calibration Procedure 6 ni.com
Both password and user-defined information have a maximum of four
ASCII-standard characters and are null-terminated strings. The user
information is empty by default and can contain any information you find
useful.
Getting Calibration Information
The NI 446Xdevices contain the current device temperature read directly
from the device and the following calibration information stored in the
EEPROM:
• Whether the device supports self-calibration
• Date and time of the last self-calibration
• Temperature during the last self-calibration
• Recommended interval for external calibration
• Date and time of the last external calibration
• Temperature during the last external calibration
You can access this information in the Measurement & Automation
Explorer (MAX) or by using the following NI-DAQmx functions.
Call DAQmxGetCalUserDefinedInfo with the following parameters:
deviceName: dev1
data: charPointerReturnValue
bufferSize: anyNumberBelowMax
LabVIEW Block Diagram
l
NI-DAQmx Function Call (Continued)

©National Instruments Corporation 7 NI 446X Calibration Procedure
NI-DAQmx Function Call
Call DAQmxGetSelfCalSupported with the following parameters:
deviceName: dev1
data: bool32PointerReturnValue
Call DAQmxGetSelfCalLastDateAndTime with the following parameters:
deviceName: dev1
year: uInt32PointerReturnValue
month: uInt32PointerReturnValue
day: uInt32PointerReturnValue
hour: uInt32PointerReturnValue
minute: uInt32PointerReturnValue
Call DAQmxGetSelfCalLastTemp with the following parameters:
deviceName: dev1
data: float64PointerReturnValue
Call DAQmxGetExtCalRecommendedInterval with the following parameters:
deviceName: dev1
data: uInt32PointerReturnValue
Call DAQmxGetExtCalLastDateAndTime with the following parameters:
deviceName: dev1
year: uInt32PointerReturnValue
month: uInt32PointerReturnValue
day: uInt32PointerReturnValue
hour: uInt32PointerReturnValue
minute: uInt32PointerReturnValue

NI 446X Calibration Procedure 8 ni.com
Call DAQmxGetExtCalLastTemp with the following parameters:
deviceName: dev1
data: float64PointerReturnValue
Call DAQmxGetCalDevTemp with the following parameters:
deviceName: dev1
data: float64PointerReturnValue
LabVIEW Block Diagram
NI-DAQmx Function Call (Continued)

©National Instruments Corporation 9 NI 446X Calibration Procedure
Test Equipment
Table 1 lists the instruments NI recommends for calibrating the NI 446X.
If the recommended instrument is not available, select a substitute
calibration standard that meets the given specifications.
Test Conditions
Follow these guidelines to optimize the connections and the environment
during verification and adjustment:
• Keep connections to the NI 446Xshort. Long cables and wires act as
antennae, picking up extra noise that can affect measurements.
• Use a 50 Ω BNC coaxial cable for all connections to the device.
• Keep relative humidity between 10 and 80%, noncondensing, or
consult the device documentation for the optimum relative humidity.
• Maintain the temperature between 18 and 28 °C, or refer to the device
specifications for the optimum temperature range.
• Allow a warm-up time of at least 15 minutes to ensure that the
measurement circuitry of the NI 446Xis at a stable operating
temperature.
• Allow a warm-up time for all the instruments and equipment,
according to the manufacturers’ instructions.
Table 1. NI 446XCalibration Equipment Specifications
Instrument Critical Specifications Suggested Model
Calibrator DC Voltage Range: 1 V, 10 V
DC Accuracy: ±300 µV*, †, ±3 mV*, †
Fluke 5700A
Function Generator Frequency Range: 1 kHz–10 kHz
Frequency Accuracy: ±2 ppm†
Voltage Range: up to 9 Vpp
HP/Agilent 33250A
Digital Multimeter DC Voltage Range: 100 mV, 1 V, 10 V
DC Accuracy: ±100 ppm†
NI 4070
*±300 µV on 1 V range, ±3 mV on 10 V range.
†This specification contains the initial accuracy and any drift due to temperature and time.

NI 446X Calibration Procedure 10 ni.com
Calibration Process
This section provides instructions for verifying and calibrating the NI 446X
device.
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. NI 446X Verification Procedure—Verify the accuracy of the device
prior to calibration.
4. NI 446X Adjustment Procedure—Perform an external calibration that
adjusts the device calibration constants with respect to known voltage
and frequency sources.
5. Perform another verification to ensure that the device operates with the
specifications after adjustment.
The self-calibration, verification, and adjustment procedures are explained
in the following sections.
Note You must compare the verification limits provided in this procedure with the most
recent specifications. Refer to the latest NI 446
X device specifications at ni.com/manuals .
Initial Setup
NI-DAQmx automatically detects all NI 446Xdevices. However, for the
driver to communicate with the device, you must configure the device in
NI-DAQmx.
Complete the following steps to configure a device in NI-DAQmx:
1. Install the NI-DAQmx driver software.
2. Power off the computer that will hold the device and install the device
in an available slot.
3. Power on the computer and launch MAX.
4. 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.

©National Instruments Corporation 11 NI 446X Calibration Procedure
Self-Calibration
Call self-calibration before completing the first verification. This function
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 446XVerification Procedure
Verification determines how well the NI 446Xdevice is meeting
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.
Verifying Analog Input Performance
This section verifies the analog input (AI) performance of all NI 446X
devices. Refer to the NI 446X Specifications for the number of channels,
gain settings, and performance specifications.
NI-DAQmx Function Call LabVIEW Block Diagram
Call DAQmxSelfCal with the following
parameters:
deviceName: dev1

NI 446X Calibration Procedure 12 ni.com
Verifying AI DC Offset
Complete the following steps to verify the AI DC offset:
1. Connect a 50 Ωterminator to the analog input channel 0 of the device.
The terminator grounds the input channel when it is in
pseudodifferential configuration.
2. If you use C function calls, create a task using the following function.
If you use LabVIEW, skip this step. The task is created in step 3 in
LabVIEW.
You use the object myTaskHandle in all subsequent NI-DAQmx
function calls.
3. Create an AI voltage channel through NI-DAQmx using the following
function.
NI-DAQmx Function Call LabVIEW Block Diagram
Call DAQmxCreateTask with the following
parameter:
taskHandle: mytaskHandleReturnValue
LabVIEW does not require this step.
NI-DAQmx Function Call LabVIEW Block Diagram
Call DAQmxCreateAIVoltageChan with the
following parameters:
taskHandle: myTaskHandle
physicalChannel: dev1/ai0
nameToAssignToChannel: ""
terminalConfig: DAQmx_Val_PseudoDiff
minVal: -10.0
maxVal: 10.0
units: DAQmx_Val_Volts
CustomScaleName: NULL

©National Instruments Corporation 13 NI 446X Calibration Procedure
4. Modify the AI voltage channel property using the following functions.
5. Configure the timing properties of the acquisition using the following
function.
6. Start the task using the following function.
NI-DAQmx Function Call LabVIEW Block Diagram
Call DAQmxSetAIGain with the
following parameters:
taskHandle: myTaskHandle
channel: dev1/ai0
data: -20.0
Call DAQmxSetAICoupling with the
following parameters:
taskHandle: myTaskHandle
channel: dev1/ai0
data: DAQmx_Val_DC
NI-DAQmx Function Call LabVIEW Block Diagram
Call DAQmxCfgSampClkTiming with
the following parameters:
taskHandle: myTaskHandle
source: NULL
rate: 204800.0
activeEdge: DAQmx_Val_Rising
sampleMode:
DAQmx_Val_FiniteSamps
sampsPerChanToAcquire: 102400
NI-DAQmx Function Call LabVIEW Block Diagram
Call DAQmxStartTask with the following
parameters:
taskHandle: myTaskHandle

NI 446X Calibration Procedure 14 ni.com
7. Acquire data using the following function.
8. Stop the task using the following function.
9. Clear the task using the following function.
NI-DAQmx Function Call LabVIEW Block Diagram
Call DAQmxReadAnalogF64 with the
following parameters:
taskHandle: myTaskHandle
numSampsPerChan: -1
timeout: 10.0
fillMode :
DAQmx_Val_GroupByChannel
arraySizeInSamps: 102400
reserved: NULL
readArray:
float64ArrayReturnValue
sampsPerChanRead:
int32PointerReturnValue
NI-DAQmx Function Call LabVIEW Block Diagram
Call DAQmxStopTask with the following
parameters:
taskHandle: myTaskHandle
NI-DAQmx Function Call LabVIEW Block Diagram
Call DAQmxClearTask with the following
parameters:
taskHandle: myTaskHandle

©National Instruments Corporation 15 NI 446X Calibration Procedure
10. Average all the values in the array returned from the acquisition. The
average is the resulting offset for AI 0 at –20 dB device gain setting.
Compare this value to the limits in Table 2.
11. Repeat steps 2 through 10 for each different gain value that is set in
step 4, using the device gain values in Table 2.
12. Repeat steps 1 through 11 for all remaining analog input channels of
the device. Replace ai0 with the appropriate channel name in function
call parameters physicalChannel and channel.
Verifying AI Gain Accuracy
Complete the following steps to verify AI gain accuracy:
1. Connect the output of the calibrator to the analog input channel 0 of the
device.
2. Output 9.0 VDC using the calibrator.
3. If you use C function calls, create a task using the following function.
If you use LabVIEW, skip this step. The task is created in step 4 in
LabVIEW.
You use the object myTaskHandle in all subsequent NI-DAQmx
function calls.
Table 2. AI Offset Limits
Device Gain
Device Input Offset
Min (mV) Max (mV)
–20 –7.0 7.0
–10 –5.0 5.0
0–0.7 0.7
10 –0.5 0.5
20 –0.2 0.2
30 –0.1 0.1
NI-DAQmx Function Call LabVIEW Block Diagram
Call DAQmxCreateTask with the following parameter:
taskHandle: mytaskHandleReturnValue
LabVIEW does not require this step.

NI 446X Calibration Procedure 16 ni.com
4. Create an AI voltage channel through NI-DAQmx using the following
function.
5. Modify the AI voltage channel property using the following functions.
NI-DAQmx Function Call LabVIEW Block Diagram
Call DAQmxCreateAIVoltageChan with the
following parameters:
taskHandle: myTaskHandle
physicalChannel: dev1/ai0
nameToAssignToChannel: ""
terminalConfig: DAQmx_Val_PseudoDiff
minVal: -10.0
maxVal: 10.0
units: DAQmx_Val_Volts
CustomScaleName: NULL
NI-DAQmx Function Call LabVIEW Block Diagram
Call DAQmxSetAIGain with the
following parameters:
taskHandle: myTaskHandle
channel: dev1/ai0
data: -20.0
Call DAQmxSetAICoupling with the
following parameters:
taskHandle: myTaskHandle
channel: dev1/ai0
data: DAQmx_Val_DC

©National Instruments Corporation 17 NI 446X Calibration Procedure
6. Configure the timing properties of the acquisition using the following
function.
7. Start the task using the following function.
NI-DAQmx Function Call LabVIEW Block Diagram
Call DAQmxCfgSampClkTiming with the
following parameters:
taskHandle: myTaskHandle
source: NULL
rate: 204800.0
activeEdge: DAQmx_Val_Rising
sampleMode : DAQmx_Val_FiniteSamps
sampsPerChanToAcquire: 102400
NI-DAQmx Function Call LabVIEW Block Diagram
Call DAQmxStartTask with the following
parameters:
taskHandle: myTaskHandle

NI 446X Calibration Procedure 18 ni.com
8. Acquire data using the following function.
9. Stop the task using the following function.
10. Clear the task using the following function.
11. Average all the values in the array returned from the acquisition. This
average is used to calculate the gain accuracy for AI 0 at –20 dB device
gain setting. Compare this value to the limits (V) in Table 3.
NI-DAQmx Function Call LabVIEW Block Diagram
Call DAQmxReadAnalogF64 with
the following parameters:
taskHandle: myTaskHandle
numSampsPerChan: -1
timeout: 10.0
fillMode:
DAQmx_Val_GroupByChannel
arraySizeInSamps: 102400
reserved: NULL
readArray:
float64ArrayReturnValue
sampsPerChanRead:
int32PointerReturnValue
NI-DAQmx Function Call LabVIEW Block Diagram
Call DAQmxStopTask with the following
parameters:
taskHandle: myTaskHandle
NI-DAQmx Function Call LabVIEW Block Diagram
Call DAQmxClearTask with the following
parameters:
taskHandle: myTaskHandle

©National Instruments Corporation 19 NI 446X Calibration Procedure
12. Repeat steps 2 through 11 for all remaining gain values used in step 5.
Modify the calibrator output amplitude in step 2. Refer to Table 3 for
the calibrator output amplitude and the device gain value.
13. Repeat steps 1 through 12 for all remaining analog input channels of
the device. Replace ai0 with the appropriate channel name in function
call parameters physicalChannel and channel.
Verifying Analog Output Performance
This section verifies the analog output (AO) performance on the NI 4461
devices. Refer to the NI 446X Specifications for the number of channels,
gain settings, and performance specifications.
Verifying AO DC Offset
Complete the following steps to verify AO DC offset:
1. Connect the analog output channel 0 of the device to the input of the
multimeter.
2. Create an array of double float of size 1024. Initialize all the values in
the array to 0.0. You use this array to output 0 V using the device
analog output channel 0.
3. If you use C function calls, create a task using the following function.
If you use LabVIEW, skip this step. The task is created in step 4 in
LabVIEW.
Table 3. AI Gain Accuracy Limits
Device Gain
Calibrator Output
Amplitude (VDC)
Device Input Amplitude Accuracy
Min (dB) Max (dB) Min (V) Max (V)
–20 9.0 –0.03 0.03 8.9690 9.0311
–10 9.0 –0.03 0.03 8.9690 9.0311
09.0 –0.03 0.03 8.9690 9.0311
10 3.0 –0.03 0.03 2.9897 3.0104
20 0.9 –0.03 0.03 0.8969 0.9031
30 0.3 –0.03 0.03 0.2990 0.3010
NI-DAQmx Function Call LabVIEW Block Diagram
Call DAQmxCreateTask with the following parameter:
taskHandle: mytaskHandleReturnValue
LabVIEW does not require this step.

NI 446X Calibration Procedure 20 ni.com
You use the object myTaskHandle in all subsequent NI-DAQmx
function calls.
4. Create an AO Voltage channel through NI-DAQmx using the following
function.
5. Modify the AO voltage channel property using the following
functions.
NI-DAQmx Function Call LabVIEW Block Diagram
Call DAQmxCreateAOVoltageChan with the
following parameters:
taskHandle: myTaskHandle
physicalChannel: dev1/ao0
nameToAssignToChannel: ""
minVal: -10.0
maxVal: 10.0
units: DAQmx_Val_Volts
customScaleName: NULL
NI-DAQmx Function Call
Call DAQmxSetAOIdleOutputBehavior with the following parameters:
taskHandle: myTaskHandle
channel: dev1/ao0
data: DAQmx_Val_HighImpedance
Call DAQmxSetAOGain with the following parameters:
taskHandle: myTaskHandle
channel: dev1/ao0
data: -40.0