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

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