National Instruments NI 6601 User manual

CALIBRATION PROCEDURE
NI 6601/6602
This document contains information and instructions for calibrating the
National Instruments 6601/6602 data acquisition devices.
Contents
Introduction............................................................................................. 2
What Is Calibration? ........................................................................ 2
Why Should You Verify? ................................................................ 2
How Often Should You Verify? ...................................................... 2
Software and Documentation.................................................................. 2
Software.................................................................................... 3
Documentation.......................................................................... 3
Test Equipment ....................................................................................... 3
Test Conditions ....................................................................................... 4
Calibration Process ................................................................................. 4
Setting Up the Stable Clock............................................................. 5
Setting Up a PXI-6608 Clock Source....................................... 5
Setting Up an Alternative Clock Source................................... 8
Connecting the Clock Source to the NI 6601/6602 Device............. 8
Connecting a PXI-6608 to the NI 6601/6602 Device............... 8
Connecting an Alternative Clock Source to the
NI 6601/6602 Device............................................................. 9
Measuring the Frequency of the NI 6601/6602 Device................... 9
Comparing the Measured Frequency to the NI 6601/6602
Device Specifications.................................................................... 17
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NI 6601/6602 Calibration Procedure 2 ni.com
Introduction
What Is Calibration?
Calibration consists of verifying the measurement accuracy of a device and
adjusting for any measurement error. For the NI 6601/6602, calibration is
simply verifying the measurement accuracy of the crystal oscillator on the
device because the crystal oscillator is not user-adjustable. Verification is
measuring the performance of a device and comparing these measurements
to the factory specifications. If the device fails after calibration, return it to
NI for repair or replacement. For more information about how to contact NI
for repair or replacement, refer to the Technical Support Information
document.
Why Should You Verify?
The accuracy of timing components drifts with time and temperature,
which can affect measurement accuracy. Verification determines whether
the device still meets NI standards.
How Often Should You Verify?
Calibrate the NI 6601/6602 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. You can
shorten this interval based on the accuracy requirements of your
application.
Software and Documentation
You will need the following software and documentation to verify the
NI 6601/6602. You can find these resources on the NI Web site at ni.com:
• Traditional NI-DAQ (Legacy) 7.4.4
•Traditional NI-DAQ (Legacy) C Function Reference Help file
•Traditional NI-DAQ User Manual document

©National Instruments Corporation 3 NI 6601/6602 Calibration Procedure
Software
This calibration procedure requires using the Traditional NI-DAQ
(Legacy) 7.4.4. Traditional NI-DAQ supports a number of application
development environments (ADEs) and programming languages,
including LabVIEW, LabWindows™/CVI™, Microsoft Visual C++,
Microsoft Visual Basic, and Borland C++. When you install the driver,
you only need to install support for the ADE or programming language you
will use.
Documentation
The Traditional NI-DAQ (Legacy) C Function Reference Help file and the
Traditional NI-DAQ User Manual document contain detailed information
about using the Traditional NI-DAQ driver. The help file includes detailed
information about the driver functions. You can access the help file by
selecting Start»All Programs»National Instruments»NI-DAQ. The
Traditional NI-DAQ User Manual document provides instructions on
installing Traditional NI-DAQ. This manual also includes detailed
information about creating applications that use the Traditional NI-DAQ
driver. These are your primary references for writing your calibration
utility. You can also refer to the documentation for the programming
language you are using. For further information about the products you are
calibrating, refer to the NI 660x User Manual.
Test Equipment
Verifying the NI 6601/6602 devices requires the following equipment:
• A highly stable 10 MHz, 5 MHz, or 1 MHz clock source that
is accurate to within 1 ppm. NI recommends using the PXI-6608 to
provide the stable clock. The PXI-6608 provides a 10 MHz clock that
is accurate to 0.075 ppm over 1 year.
• An SH68-68-D1 cable or a standard 68-pin cable connector
• A 68-pin breakout box (if you are using a clock source other than the
PXI-6608)

NI 6601/6602 Calibration Procedure 4 ni.com
Test Conditions
Follow these guidelines to optimize the equipment and the environment
during calibration:
• Keep connections to the device as short as possible. Long cables and
wires act as antennae by picking up extra noise that can affect
measurements.
• Maintain an ambient temperature of approximately 25 °C.
• Keep relative humidity below 80%.
• Use shielded copper wire for all cable connections to the device.
Use twisted-pair wire to eliminate noise and thermal offsets.
• Allow a warm-up time of at least 15 minutes to ensure the
measurement circuitry is at a stable operating temperature.
Calibration Process
This section contains instructions for verifying the operation of the crystal
oscillator on the NI 6601/6602 devices using a stable clock source.
Verifying the performance of the oscillator on an NI 6601/6602 device
requires two counters on the NI 6601/6602 device—counters 0 and 1.
Counter 1 uses a stable clock as the source to generate a 50 ms single pulse,
which is applied to the GATE of counter 0. The 20 MHz timebase on the
NI 6601/6602 device, which is derived from the crystal oscillator, is the
SOURCE of counter 0. You will count the number of clock edges of the
20 MHz timebase that occur during the 50 ms single pulse and calculate the
frequency of the oscillator to determine if the device is within its
specifications. Figure 1 shows a simple diagram of the process.
Figure 1. NI 6601/6602 Verification Process
50 ms
CTR 1 CTR 0
Stable Clock Source 20 MHz Timebase
Source Source
Gate
Output

©National Instruments Corporation 5 NI 6601/6602 Calibration Procedure
The frequency measurement will have an uncertainty that is equal to the
sum of the stable clock error and the quantization error caused by the
counter. The clock error should be 1 ppm or less, as specified in the Test
Equipment section of this document. The quantization error, which is the
inherent uncertainty in digitizing an analog value, will always be up to
50 ns. Using a measurement duration of 50 ms gives a quantization error
as follows:
The sum of the stable clock error, 1 ppm, and the quantization error,
1 ppm, gives a total measurement uncertainty of 2 ppm. You can reduce
measurement uncertainty by using a more stable clock, by increasing the
measurement duration, or both. The calculations presented at the end of this
document allow for a 2 ppm measurement uncertainty.
Both Traditional NI-DAQ and LabVIEW programming instructions are
presented in the following sections. Choose the appropriate instructions for
your programming environment.
Setting Up the Stable Clock
This section describes how to set up the clock. NI recommends using the
PXI-6608 to provide the stable clock. You can use an alternative stable
clock if it meets the specifications described in the Test Equipment section
of this document. Instructions for both clock alternatives are included in the
following two sections, Setting Up a PXI-6608 Clock Source and Setting
Up an Alternative Clock Source.
Setting Up a PXI-6608 Clock Source
To set up a PXI-6608 as the stable clock source, complete the following
steps:
1. Power on the 6608 device.
2. Wait 15 minutes to allow the measurement circuitry in the device
to warm up.
50 ns
50 ms
-------------- 1 ppm=

NI 6601/6602 Calibration Procedure 6 ni.com
3. Route the 10 MHz stable clock of the PXI-6608 onto PFI_35.
a. Configure counter 1 on the PXI-6608 to perform simple event
counting.
b. Configure the source of counter 1 as RTSI line 0.
Traditional NI-DAQ Function Call LabVIEW Block Diagram
Call GPCTR_Set_Application with the
following parameters:
deviceNumber: The value set by
Measurement & Automation Explorer
(MAX)
gpctrNum: ND_COUNTER_1
application: ND_SIMPLE_EVENT_CNT
Traditional NI-DAQ Function Call LabVIEW Block Diagram
Call GPCTR_Change_Parameter with
the following parameters:
deviceNumber: The value set by MAX
gpctrNum: ND_COUNTER_1
paramID: ND_SOURCE
paramValue: ND_RTSI_0

©National Instruments Corporation 7 NI 6601/6602 Calibration Procedure
c. Route the stable 10 MHz clock on the PXI-6608 onto RTSI line 0.
d. Configure the source of counter 1 to be available on PFI line 35.
Traditional NI-DAQ Function Call LabVIEW Block Diagram
Call Select_Signal with the following
parameters:
deviceNumber: The value set by MAX
signal: ND_RTSI_0
source: ND_STABLE_10_MHZ
sourceSpec: ND_DONT_CARE
Traditional NI-DAQ Function Call LabVIEW Block Diagram
Call Select_Signal with the following
parameters:
deviceNumber: The value set by MAX
signal: ND_PFI_35
source: ND_GPCTR1_SOURCE
sourceSpec: ND_DONT_CARE

NI 6601/6602 Calibration Procedure 8 ni.com
e. Program counter 1 to arm it.
Setting Up an Alternative Clock Source
To set up a clock source other than a PXI-6608, complete the following
steps:
1. Ensure that the clock source meets the requirements listed in the Test
Equipment section.
2. Power the clock device.
Note After you complete the clock setup procedure, the clock is running and generating
pulses.
Connecting the Clock Source to the NI 6601/6602 Device
This section describes how to connect the clock source to the NI 6601/6602
device, whether you are using a PXI-6608 or another clock source.
Connecting a PXI-6608 to the NI 6601/6602 Device
Connect the PXI-6608 clock source to the NI 6601/6602 device using an
SH68-68-D1 cable, which connects to the I/O connector of each device.
Traditional NI-DAQ Function Call LabVIEW Block Diagram
Call GPCTR_Control with the following
parameters:
deviceNumber: The value set by MAX
gpctrNum: ND_COUNTER_1
action: ND_PROGRAM
“TASK ID” out connects to “TASK ID” in of step 14
in the Measuring the Frequency of the NI 6601/6602
Device section.

©National Instruments Corporation 9 NI 6601/6602 Calibration Procedure
Connecting an Alternative Clock Source to the
NI 6601/6602 Device
To connect an alternative clock source to the NI 6601/6602 device,
complete the following steps:
1. Connect the NI 6601/6602 device to a 68-pin breakout box using the
SH68-68-D1 cable.
2. Connect the clock source to pins 7 and 41 of the 68-pin breakout box
using twisted-pair wires.
• Connect the clock to pin 7. Pin 7 corresponds to PFI_35, which is
the SOURCE of counter 1 on all NI 6601/6602 devices.
• Connect the ground of the clock to pin 41, which is digital ground.
Measuring the Frequency of the NI 6601/6602 Device
Note If you are verifying the PXI-6602 on a PXI chassis, the measured frequency is that
of the PXI backplane clock instead of the onboard oscillator. To verify the onboard
oscillator, you must calibrate the PXI-6602 on a PCI chassis using a CompactPCI-to-PCI
adapter.
To measure the frequency of the NI 6601/6602 device for verification,
complete the following steps:
1. Configure counter 0 to perform simple event counting.
Traditional NI-DAQ Function Call LabVIEW Block Diagram
Call GPCTR_Set_Application with the
following parameters:
deviceNumber: The value set by MAX
gpctrNum: ND_COUNTER_0
application: ND_SIMPLE_EVENT_CNT

NI 6601/6602 Calibration Procedure 10 ni.com
2. Set the source of counter 0 to be the 20 MHz timebase.
3. Configure the gate of counter 0 to be the output of counter 1.
Traditional NI-DAQ Function Call LabVIEW Block Diagram
Call GPCTR_Change_Parameter with
the following parameters:
deviceNumber: The value set by MAX
gpctrNum: ND_COUNTER_0
paramID: ND_SOURCE
paramValue: ND_INTERNAL_20_MHZ
Traditional NI-DAQ Function Call LabVIEW Block Diagram
Call GPCTR_Change_Parameter with
the following parameters:
deviceNumber: The value set by MAX
gpctrNum: ND_COUNTER_0
paramID: ND_GATE
paramValue:
ND_OTHER_GPCTR_OUTPUT