National Instruments NI 6731, NI 6711, NI 6713, NI 6733 Calibration Procedure

NI 6711/6713/6731/6733 C

ALIBRATIONPROCEDURE

Introduction

This document contains step-by-step instructions for calibrating National Instruments 6711/6713/6731/6733 for PCI/PXI/CompactPCI analog output (AO) devices. Use this calibration procedure in conjunction with the for calibrating NI 6711/6713/6731/6733 devices.

ni671xCal.dll

file, which contains specific functions required

Refer to

Note

ni671xCal.dll

ni.com/support/calibrat/mancal.htm

file.

What Is Calibration?

Calibration consists of verifying the measurement accuracy of a device and adjusting for any measurement error. Verification is measuring the performance of the device and comparing these measurements to the factory specifications. During calibration, you supply and read voltage levels using external standards, then you adjust the module calibration constants. The new calibration constants are stored in the EEPROM. The calibration constants are loaded from memory as needed to adjust for the error in the measurements taken by the device.

Why Should You Calibrate?

The accuracy of electronic components drifts with time and temperature, which can affect measurement accuracy as the device ages. Calibration restores these components to their specified accuracy and ensures that the device still meets NI standards.

for a copy of the

CVI™, LabVIEW™, National Instruments™, NI™, ni.com™, and NI-DAQ™ are trademarks of National Instruments Corporation. Product and company names mentioned herein are trademarks or trade names of their respective companies. For patents covering National Instruments products, refer to the appropriate location: Help»Patents in your software, the patents.txt file on your CD, or ni.com/patents.

ni.com

May 2002

370555A-01

How Often Should You Calibrate?

The measurement requirements of your application determine how often the NI 6711/6713/6731/6733 must be calibrated to maintain accuracy. NI recommends that you perform a complete calibration at least once every year. You can shorten this interval to 90 days or six months based on the demands of your application.

Calibration Options: External Versus Internal

The NI 6711/6713/6731/6733 has two calibration options: an internal, or self-calibration, and an external calibration.

Internal Calibration

Internal calibration is a much simpler calibration method that does not rely on external standards. In this method, the device calibration constants are adjusted with respect to a high-precision voltage source on the NI 6711/6713/6731/6733. This type of calibration is used after the device has been calibrated with respect to an external standard. However, external variables such as temperature can still affect measurements. The new calibration constants are defined with respect to the calibration constants created during an external calibration, ensuring that the measurements can be traced back to the external standards. In essence, internal calibration is similar to the auto-zero function found on a digital multimeter (DMM).

External Calibration

External calibration requires using a high-precision DMM. During external calibration, the DMM supplies and reads voltages from the device. Adjustments are made to the device calibration constants to ensure that the reported voltages fall within the device specifications. The new calibration constants are then stored in the device EEPROM. After the onboard calibration constants have been adjusted, the high-precision voltage source on the device is adjusted. An external calibration provides a set of calibration constants that you can use to compensate for the error in the measurements taken by the NI 6711/6713/6731/6733.

NI 6711/6713/6731/6733 Calibration Procedure 2 ni.com

Equipment and Other Test Requirements

This section describes the equipment, test conditions, documentation, and software you need to calibrate the NI 6711/6713/6731/6733.

Test Equipment

To calibrate the NI 6711/6713/6731/6733, you need a high-precision DMM that is at least 10 ppm (0.001%) accurate. NI recommends that you use the Agilent 3458A DMM for calibration.

If you do not have an Agilent 3458A DMM, use the accuracy specifications to select a substitute calibration standard.

If you do not have custom connection hardware, you may need a connector block such as the NI CB-68 and a cable such as the SH6868-D1. These components give you easy access to the individual pins on the 68-pin I/O connector.

Test Conditions

Follow these guidelines to optimize connections and test conditions during calibration:

• Keep connections to the NI 6711/6713/6731/6733 short. Long cables and wires act as antennae, picking up extra noise, which can affect measurements.

• Use shielded copper wire for all cable connections to the device.

• Use twisted-pair wire to eliminate noise and thermal offsets.

• Maintain a temperature between 18 and 28 °C. To operate the module at a specific temperature outside this range, calibrate the device at that temperature.

• Keep relative humidity below 80%.

• Allow a warm-up time of at least 15 minutes to ensure that the measurement circuitry is at a stable operating temperature.

Software

Because the NI 6711/6713/6731/6733 is a PC-based measurement device, you must have the proper device driver installed in the calibration system before attempting calibration. For this calibration procedure, you need NI-DAQ version 6.9.2 or earlier installed on the calibration computer. NI-DAQ, which configures and controls the NI 6711/6713/6731/6733, is available at

ni.com/downloads

NI-DAQ supports a number of 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 programming language that you intend to use.

You also need copies of the

ni671xCal.h

The DLL provides calibration functionality that does not reside in NI-DAQ, including the ability to protect the calibration constants, update the calibration date, and write to the factory calibration area. You can access the functions in this DLL through any 32-bit compiler. The factory calibration area and the calibration date should only be modified by a metrology laboratory or another facility that maintains traceable standards.

files.

ni671xCal.dll,ni671xCal.lib

,and

Configuring the NI 6711/6713/6731/6733

The NI 6711/6713/6731/6733 must be configured in NI-DAQ, which automatically detects the device. The following steps briefly explain how to configure the device in NI-DAQ. Refer to the NI 671X/673X User Manual for detailed installation instructions. You can install this manual when you install NI-DAQ.

1. Power down the computer.

2. Install the NI 6711/6713/6731/6733 in an available slot.

3. Power on the computer.

4. Launch Measurement & Automation Explorer (MAX).

5. Configure the NI 6711/6713/6731/6733 device number.

6. Click Test Resources to ensure that the NI 6711/6713/6731/6733 is

properly working.

The NI 6711/6713/6731/6733 is now configured.

Note

After a device is configured in MAX, the device is assigned a device number, which

is used in each of the function calls to identify which DAQ device to calibrate.

Writing the Calibration Procedure

The calibration procedure in the Calibrating the NI 6711/6713/6731/6733 section provides step-by-step instructions on calling the appropriate calibration functions. These calibration functions are C function calls from NI-DAQ that are also valid for Microsoft Visual Basic and Microsoft Visual C++ programs. Although LabVIEW VIs are not discussed in this procedure, you can program in LabVIEW using the VIs that have similar names to the NI-DAQ function calls in this procedure. Refer to the

NI 6711/6713/6731/6733 Calibration Procedure 4 ni.com

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