National Instruments DAQMeter DAQCard-4050 User manual

DAQMeter
DAQCard-4050
User Manual
Digital Multimeter Card for PCMCIA
DAQMeter DAQCard-4050 User Manual
February 1997 Edition
Part Number 321427A-01
© Copyright 1997 National Instruments Corporation. All Rights Reserved.

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Important Information
Warranty
The DAQMeter DAQCard-4050 is warranted against defects in materials and workmanship for a period of one year
from the date of shipment, as evidenced by receipts or other documentation. National Instruments will, at its option,
repair or replace equipment that proves to be defective during the warranty period. This warranty includes parts and
labor.
The media on which you receive National Instruments software are warranted not to fail to execute programming
instructions, due to defects in materials and workmanship, for a period of 90 days from date of shipment, as evidenced
by receipts or other documentation. National Instruments will, at its option, repair or replace software media that do
not execute programming instructions if National Instruments receives notice of such defects during the warranty
period. National Instruments does not warrant that the operation of the software shall be uninterrupted or error free.
A Return Material Authorization (RMA) number must be obtained from the factory and clearly marked on the outside
of the package before any equipment will be accepted for warranty work. National Instruments will pay the shipping
costs of returning to the owner parts which are covered by warranty.
National Instruments believes that the information in this manual is accurate. The document has been carefully
reviewed for technical accuracy. In the event that technical or typographical errors exist, National Instruments reserves
the right to make changes to subsequent editions of this document without prior notice to holders of this edition. The
reader should consult National Instruments if errors are suspected. In no event shall National Instruments be liable for
any damages arising out of or related to this document or the information contained in it.
EXCEPT AS SPECIFIED HEREIN, NATIONAL INSTRUMENTS MAKES NO WARRANTIES, EXPRESS OR IMPLIED, AND
SPECIFICALLY DISCLAIMS ANY WARRANTY OF MERCHANTABILITY OR FITNESS FOR APARTICULAR PURPOSE.
CUSTOMER’SRIGHT TO RECOVER DAMAGES CAUSED BY FAULT OR NEGLIGENCE ON THE PART OF NATIONAL
INSTRUMENTS SHALL BE LIMITED TO THE AMOUNT THERETOFORE PAID BY THE CUSTOMER. NATIONAL INSTRUMENTS
WILL NOT BE LIABLE FOR DAMAGES RESULTING FROM LOSS OF DATA, PROFITS, USE OF PRODUCTS, OR INCIDENTAL OR
CONSEQUENTIAL DAMAGES, EVEN IF ADVISED OF THE POSSIBILITY THEREOF. This limitation of the liability of National
Instruments will apply regardless of the form of action, whether in contract or tort, including negligence. Any action
against National Instruments must be brought within one year after the cause of action accrues. National Instruments
shall not be liable for any delay in performance due to causes beyond its reasonable control. The warranty provided
herein does not cover damages, defects, malfunctions, or service failures caused by owner’s failure to follow the
National Instruments installation, operation, or maintenance instructions; owner’s modification of the product;
owner’s abuse, misuse, or negligent acts; and power failure or surges, fire, flood, accident, actions of third parties, or
other events outside reasonable control.
Copyright
Under the copyright laws, this publication may not be reproduced or transmitted in any form, electronic or mechanical,
including photocopying, recording, storing in an information retrieval system, or translating, in whole or in part,
without the prior written consent of National Instruments Corporation.
Trademarks
LabVIEW®, NI-DAQ®, ComponentWorks™, CVI™, DAQCard™, DAQMeter™, SCXI™, and VirtualBench™ are
trademarks of National Instruments Corporation.
Product and company names listed are trademarks or trade names of their respective companies.
WARNING REGARDING MEDICAL AND CLINICAL USE OF NATIONAL INSTRUMENTS PRODUCTS
National Instruments products are not designed with components and testing intended to ensure a level of reliability
suitable for use in treatment and diagnosis of humans. Applications of National Instruments products involving
medical or clinical treatment can create a potential for accidental injury caused by product failure, or by errors on the
part of the user or application designer. Any use or application of National Instruments products for or involving
medical or clinical treatment must be performed by properly trained and qualified medical personnel, and all traditional
medical safeguards, equipment, and procedures that are appropriate in the particular situation to prevent serious injury
or death should always continue to be used when National Instruments products are being used. National Instruments
products are NOT intended to be a substitute for any form of established process, procedure, or equipment used to
monitor or safeguard human health and safety in medical or clinical treatment.

© National Instruments Corporation v DAQMeter DAQCard-4050 User Manual
Table
of
Contents
About This Manual
Organization of This Manual........................................................................................ix
Conventions Used in This Manual................................................................................x
National Instruments Documentation...........................................................................x
Related Documentation.................................................................................................xi
Customer Communication............................................................................................xi
Chapter 1
Introduction
About the DAQMeter DAQCard-4050.........................................................................1-1
What You Need to Get Started .....................................................................................1-2
Software Programming Choices...................................................................................1-2
National Instruments Application Software...................................................1-2
VirtualBench...................................................................................................1-3
DAQMeter DAQCard-4050 Instrument Driver and NI-DAQ .......................1-3
Optional Equipment......................................................................................................1-5
Unpacking.....................................................................................................................1-5
Chapter 2
Installation and Configuration
Safety Instructions ........................................................................................................2-1
Installation ....................................................................................................................2-2
Cable and Probes ..........................................................................................................2-3
Hardware Configuration ...............................................................................................2-4
Chapter 3
DMM Operation
Warm-up.......................................................................................................................3-1
Choosing a Reading Rate..............................................................................................3-1
Measuring Voltages......................................................................................................3-2
DC Voltages ...................................................................................................3-3
Input Ranges ....................................................................................3-3

Table of Contents
DAQMeter DAQCard-4050 User Manual vi
© National Instruments Corporation
Accuracy Considerations................................................................. 3-3
Input Impedance................................................................ 3-3
AC Noise Effects............................................................... 3-4
Thermal EMF.................................................................... 3-4
AC Voltages................................................................................................... 3-5
True RMS Method........................................................................... 3-5
Input Ranges.................................................................................... 3-5
Accuracy Considerations................................................................. 3-6
Frequency Response.......................................................... 3-6
Crest Factor....................................................................... 3-7
AC Voltage Offset............................................................. 3-8
Measuring Resistance................................................................................................... 3-8
Signal Connections ........................................................................................ 3-8
Input Ranges .................................................................................................. 3-9
Continuity Measurements .............................................................................. 3-10
Testing Diodes.............................................................................................................. 3-10
Signal Connections ........................................................................................ 3-10
Measuring Current........................................................................................................ 3-11
Appendix A
Specifications
Appendix B
PC Card Questions and Answers
Appendix C
Customer Communication
Glossary
Index

Table of Contents
© National Instruments Corporation vii DAQMeter DAQCard-4050 User Manual
Figures
Figure 1-1. The Relationship between the Programming Environment,
NI-DAQ, and Your Hardware ...............................................................1-4
Figure 2-1. Installing the DAQCard-4050 and Cables.............................................2-3
Figure 2-2. Probe Types ...........................................................................................2-4
Figure 3-1. Connecting Probes for Voltage Measurement.......................................3-2
Figure 3-2. The Effect of Input Impedance on Signal Measurement.......................3-4
Figure 3-3. Connections for Resistance Measurement.............................................3-8
Figure 3-4. Connections for Diode Measurement....................................................3-10
Figure 3-5. Connections for Current Measurement..................................................3-11
Tables
Table 3-1. DC Input Range Accuracy.....................................................................3-3
Table 3-2. AC Input Range Accuracy.....................................................................3-6
Table 3-3. Input Frequency Error Rate...................................................................3-7
Table 3-4. Crest Factor Error Rate..........................................................................3-7
Table 3-5. Resistance Input Range Accuracy .........................................................3-9

© National Instruments Corporation ix DAQMeter DAQCard-4050 User Manual
About
This
Manual
This manual describes the electrical and mechanical aspects of the
DAQMeter DAQCard-4050 and contains information concerning its
operation and programming.
The DAQMeter DAQCard-4050 is a digital multimeter card for
computers with Type II PCMCIA slots compliant with revision 2.1
of the PCMCIA specifications.
Organization of This Manual
The DAQMeter DAQCard-4050 User Manual is organized as follows:
• Chapter 1, Introduction, describes the DAQMeter DAQCard-4050,
lists what you need to get started, describes the optional software
and optional equipment, and explains how to unpack your card.
• Chapter 2, Installation and Configuration, explains safety
instructions and describes how to install and configure a
DAQMeter DAQCard-4050.
• Chapter 3, DMM Operation, describes how to use your DAQMeter
DAQCard-4050 and includes operation tips on taking voltage,
resistance, diode, and current readings.
• Appendix A, Specifications, lists the specifications for the
DAQMeter DAQCard-4050.
• Appendix B, PC Card Questions and Answers, contains a list of
common questions and answers relating to PC Card (PCMCIA)
operation.
• Appendix C, Customer Communication, contains forms you can
use to request help from National Instruments or to comment on our
products.
•TheGlossary contains an alphabetical list and description of terms
used in this manual, including acronyms, abbreviations, metric
prefixes, mnemonics, and symbols.
•TheIndex alphabetically lists topics covered in this manual,
including the page where you can find the topic.

About This Manual
DAQMeter DAQCard-4050 User Manual x
© National Instruments Corporation
Conventions Used in This Manual
The following conventions are used in this manual:
bold Bold text denotes the names of menus, menu items, parameters, dialog
boxes, dialog box buttons or options, icons, windows, Windows 95 tabs,
or LEDs.
bold italic Bold italic text denotes a note, caution, or warning.
italic Italic text denotes emphasis, a cross reference, or an introduction to a
key concept. This font also denotes text from which you supply the
appropriate word or value, as in Windows 3.x.
monospace Text in this font denotes text or characters that should literally 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, and
for statements and comments taken from programs.
The Glossary lists abbreviations, acronyms, metric prefixes,
mnemonics, symbols, and terms.
National Instruments Documentation
The DAQMeter DAQCard-4050 User Manual is one piece of the
documentation set for your DAQ system. You could have any of several
types of manuals depending on the hardware and software in your
system. Use the manuals you have as follows:
• Your DAQ hardware user manuals—These manuals have detailed
information about the DAQ hardware that plugs into or is
connected to your computer. Use these manuals for hardware
installation and configuration instructions, specification
information about your DAQ hardware, and application hints.
• Software documentation—You might have several sets of software
documentation, including LabVIEW, LabWindows®/CVI,
VirtualBench, and NI-DAQ. After you have set up your hardware
system, use either the application software (LabVIEW or
LabWindows/CVI) or the NI-DAQ documentation to help you write
your application. If you have a large and complicated system, it is
worthwhile to look through the software documentation before you
configure your hardware.

About This Manual
© National Instruments Corporation xi DAQMeter DAQCard-4050 User Manual
• Accessory installation guides or manuals—If you are using
accessory products, read the terminal block and cable assembly
installation guides. They explain how to physically connect the
relevant pieces of the system. Consult these guides when you are
making your connections.
Related Documentation
The following document contains information that you may find
helpful:
• Your computer user manual
Customer Communication
National Instruments wants to receive your comments on our products
and manuals. We are interested in the applications you develop with our
products, and we want to help if you have problems with them. To make
it easy for you to contact us, this manual contains comment and
configuration forms for you to complete. These forms are in
Appendix C, Customer Communication, at the end of this manual.

© National Instruments Corporation 1-1 DAQMeter DAQCard-4050 User Manual
Chapter
1
Introduction
This chapter describes the DAQMeter DAQCard-4050, lists what you
need to get started, describes the optional software and optional
equipment, and explains how to unpack your card.
About the DAQMeter DAQCard-4050
Thank you for buying a National Instruments DAQMeter
DAQCard-4050. The DAQCard-4050 is a digital multimeter card
for computers equipped with Type II PCMCIA slots.
The DAQCard-4050 features accurate 5 1/2-digit DC voltage, true
root mean square (RMS) AC voltage, ohm, and diode measurements
in a PC Card format. You can use the card to make the same
measurements you would with a standard benchtop digital multimeter.
The DAQCard-4050 contains a 24-bit analog-to-digital converter
(ADC) with digital filtering, which gives the card excellent resolution,
accuracy, and noise rejection. Coupled with a CSM series current shunt
module available from National Instruments, the DAQCard-4050 also
effectively measures AC and DC current.
The DAQCard-4050’s small size, weight, and low power consumption
make this device ideal for use in portable computers, which makes
remote measurements and data-logging practical. The DAQCard-4050
requires very little power when in operation, thus extending the life of
your computer batteries.
A system based on the DAQCard-4050 offers the flexibility,
performance, and size that makes it ideal for service, repair, and
manufacturing as well as for use in industrial and laboratory
environments. The DAQCard-4050, used in conjunction with your
computer, is a versatile, cost-effective platform for high-resolution
measurements.
Detailed specifications for the DAQCard-4050 are in Appendix A,
Specifications.

Chapter 1 Introduction
DAQMeter DAQCard-4050 User Manual 1-2
© National Instruments Corporation
What You Need to Get Started
To set up and use your DAQCard-4050, you will need the following:
❑DAQMeter DAQCard-4050
❑DAQMeter DAQCard-4050 User Manual
❑One of the following software packages and documentation:
– NI-DAQ for PC compatibles
– LabVIEW for PC compatibles
– LabWindows/CVI
–VirtualBench
– DAQMeter DAQCard-4050 Instrument Driver
❑DAQMeter DAQCard-4050 accessory cable
❑One pair of test probes (red and black)
❑Your computer
Software Programming Choices
There are several options to choose from to program and use your
National Instruments DAQ hardware. You can use LabVIEW,
LabWindows/CVI, VirtualBench, or the DAQMeter DAQCard-4050
Instrument Driver.
National Instruments Application Software
LabVIEW and LabWindows/CVI are innovative program development
software packages for data acquisition and control applications.
LabVIEW uses graphical programming, whereas LabWindows/CVI
enhances traditional programming languages. Both packages include
extensive libraries for data acquisition, instrument control, data
analysis, and graphical data presentation.
LabVIEW features interactive graphics, a state-of-the-art user
interface, and a powerful graphical programming language. The
LabVIEW Data Acquisition VI Library, a series of VIs for using
LabVIEW with National Instruments DAQ hardware, is included with

Chapter 1 Introduction
© National Instruments Corporation 1-3 DAQMeter DAQCard-4050 User Manual
LabVIEW. The LabVIEW Data Acquisition VI Library is functionally
equivalent to the NI-DAQ software.
LabWindows/CVI features interactive graphics, a state-of-the-art user
interface, and uses the ANSI standard C programming language. The
LabWindows/CVI Data Acquisition Library, a series of functions for
using LabWindows/CVI with National Instruments DAQ hardware, is
included with the NI-DAQ software kit. The LabWindows/CVI Data
Acquisition library is functionally equivalent to the NI-DAQ software.
However, the DAQCard-4050 works only with the Easy I/O functions.
For full functionality, you can use the DAQMeter DAQCard-4050
Instrument Driver with LabWindows/CVI.
Using LabVIEW or LabWindows/CVI software will greatly reduce the
development time for your data acquisition and control application.
VirtualBench
VirtualBench is a suite of VIs that allow you to use your data
acquisition products just as you use stand-alone instruments, but you
benefit from the processing, display, and storage capabilities of PCs.
VirtualBench instruments load and save waveform data to disk in the
same forms that can be used in popular spreadsheet programs and word
processors. A report generation capability complements the raw data
storage by adding timestamps, measurements, user name, and
comments.
The complete VirtualBench suite contains VirtualBench-Scope,
VirtualBench-DSA, VirtualBench-Function Generator,
VirtualBench-FG, VirtualBench-Arb, VirtualBench-AODC,
VirtualBench-DIO, VirtualBench-Board Calibrator,
VirtualBench-DMM, and VirtualBench-Logger. Your DAQCard-4050
kits contains a copy of VirtualBench-DMM. VirtualBench-DMM is a
turn-key application that allows you to make measurements as you
would with a standard benchtop multimeter.
DAQMeter DAQCard-4050 Instrument Driver and NI-DAQ
The DAQMeter DAQCard-4050 Instrument Driver provides flexibility
and programmability in a standard instrument driver format.
The instrument driver application programming interface (API) is
designed after a classical, full-featured digital multimeter instrument
driver. The instrument driver lets you avoid making low-level software
calls. The DAQMeter DAQCard-4050 Instrument Driver works with

Chapter 1 Introduction
DAQMeter DAQCard-4050 User Manual 1-4
© National Instruments Corporation
LabVIEW, LabWindows/CVI, or conventional programming languages
such as C and Visual Basic.
While you can do most programming at the instrument driver level, you
can use NI-DAQ for complete control over the card’s functionality as
well as for integrating your system into larger NationalInstruments data
acquisition systems.
Whether you are using the DAQMeter DAQCard-4050 Instrument
Driver, LabVIEW, or LabWindows/CVI, your application uses the
NI-DAQ driver software, as illustrated in Figure 1-1.
Figure 1-1. The Relationship between the Programming Environment,
NI-DAQ, and Your Hardware
LabWindows/CVI*
(Windows 95, 3.1, or NT)
*Easy I/O functions only
LabVIEW
(Windows 95, 3.1, or NT)
Conventional
Programming Languages
(C, Visual Basic)
(Windows 95 or NT)
VirtualBench
(Windows 95, 3.1) NI-DAQ Driver Software
DAQ or
SCXI Hardware
Personal
Computer or
Workstation
DAQMeter
DAQCard-4050
Instrument Driver

Chapter 1 Introduction
© National Instruments Corporation 1-5 DAQMeter DAQCard-4050 User Manual
Optional Equipment
National Instruments offers a variety of products to use with your
DAQCard-4050, including cables, connector blocks, and other
accessories, as follows:
• Current shunt modules for making current measurements
• Additional test probes and accessories to simplify making
measurements
For more specific information about these products, refer to your
National Instruments catalogue or website, or call the office nearest
you.
Unpacking
Your DAQCard-4050 is shipped in an antistatic vinyl box. When you
are not using your DAQCard-4050, store it in this box. Because your
DAQCard-4050 is enclosed in a fully shielded case, no additional
electrostatic precautions are necessary. However, for your own safety
and to protect your DAQCard-4050, never attempt to touch the
connector pins.

© National Instruments Corporation 2-1 DAQMeter DAQCard-4050 User Manual
Chapter
2
Installation and
Configuration
This chapter explains safety instructions and describes how to install
and configure a DAQMeter DAQCard-4050.
Safety Instructions
Caution: DO NOT OPERATE THIS DEVICE IN AN EXPLOSIVE ATMOSPHERE
OR WHERE THERE MAY BE FLAMMABLE GASES OR FUMES.
Equipment described in this document must be used in an Installation
Category II environment per IEC 664. This category requires local level
supply mains-connected installation.
To prevent safety hazards, the maximum voltage between either of the
inputs and the ground of the computer should never exceed ±250 VDC
or 250 Vrms.
DO NOT OPERATE DAMAGED EQUIPMENT. The safety protection
features built into this device can become impaired if the device becomes
damaged in any way. If the device is damaged, do not use until
service-trained personnel can check its safety. If necessary, return the
device to National Instruments for service and repair to ensure that its
safety is not compromised.
Do not operate this equipment in a manner that contradicts the
information specified in this document. Misuse of this equipment could
result in a shock hazard.
DO NOT SUBSTITUTE PARTS OR MODIFY EQUIPMENT. Because of
the danger of introducing additional hazards, do not install unauthorized
parts or modify the device. Return the device to National Instruments for
service and repair to ensure that its safety is not compromised.
!

Chapter 2 Installation and Configuration
DAQMeter DAQCard-4050 User Manual 2-2
© National Instruments Corporation
Connections that exceed any of the maximum signal ratings on the
DAQCard-4050 can create a shock or fire hazard or can damage any or all
of the devices connected to the DAQCard-4050. National Instruments is
NOT LIABLE FOR ANY DAMAGES OR INJURIES resulting from
incorrect signal connections.
Clean devices and accessories by brushing off light dust with a soft,
nonmetallic brush. Remove other contaminants with a stiff nonmetallic
brush. The unit must be completely dry and free from contaminants before
returning to service.
Installation
Note: You should install your driver software before installing your hardware.
Refer to the DAQMeter DAQCard-4050 Read Me First document for
software installation instructions.
There are two basic steps to installing a DAQCard-4050:
1. If you have Windows 3.1, you must have Card & Socket Services
2.0 (or a later version) software installed on your computer. If you
have Windows 95, you do not need Card & Socket Services. These
services are built into the Windows 95 operating system.
2. Insert the DAQCard-4050 and attach the DAQCard-4050 accessory
cable.
The DAQCard-4050 has two connectors—a 68-pin PCMCIA bus
connector on one end and a 4-pin I/O connector on the other end.
Insert the PCMCIA bus connector into any available Type II
PCMCIA slot until the connector is seated firmly. Notice that the
DAQCard-4050 and the DAQCard-4050 accessory cable are both
keyed so that the cable can be inserted only one way.
Be careful not to put strain on the DAQCard-4050 accessory cable
when inserting it into and removing it from the DAQCard-4050.
Always grasp the cable by the connector you are plugging or
unplugging. Never pull directly on the DAQCard-4050 accessory
cable to unplug it from the DAQCard-4050.
The DAQCard-4050 is now installed.

Chapter 2 Installation and Configuration
© National Instruments Corporation 2-3 DAQMeter DAQCard-4050 User Manual
Cable and Probes
The DAQCard-4050 kit contains the DAQCard-4050 accessory cable,
which connects the DAQCard-4050 to a pair of test probes with
shrouded banana plugs. These probes are also included in the kit. Both
the DAQCard-4050 accessory cable and the test probes meet
international safety requirements including UL 3111 and IEC 1010-1
for the full ranges of applications supported by the DAQCard-4050.
Before using any probes or accessories not supplied by National
Instruments, ensure that they meet applicable safety requirements for
the signal levels you may encounter.
To use the DAQCard-4050 accessory cable and probes with the
DAQCard-4050, first connect the cable to the card as shown in
Figure 2-1. The accessory cable connector is polarized so that it cannot
be plugged in incorrectly.
Figure 2-1. Installing the DAQCard-4050 and Cables
PCMCIA Slot
Portable
Computer
DAQCard-4050
Probes
Accessory Cable

Chapter 2 Installation and Configuration
DAQMeter DAQCard-4050 User Manual 2-4
© National Instruments Corporation
The test probes connect to the DAQCard-4050 accessory cable via
shrouded banana jacks. The shrouds around the banana jacks prevent
you from contacting potentially hazardous voltages connected to the
test probes. You can also connect the cable to standard (unshrouded)
banana jack probes or accessories; however, use unshrouded probes or
accessories only when the voltages are less than 30 Vrms or 42 Vpk-to-pk.
You can use the measurement ends of the test probes in either of two
ways, as shown in Figure 2-2. With the plastic covers over the ends, you
can use the probes to directly probe the circuit or device to be tested.
With the plastic tip covers removed, the test probes can accept standard
banana jack accessories (such as spade lugs, alligator clips, or spring
clips), which are available from National Instruments.
Figure 2-2. Probe Types
Hardware Configuration
The DAQCard-4050 is a fully software-configurable, Plug and Play
device. Configuration information is stored in nonvolatile memory. The
Plug and Play services query the device, read the information, and
arbitrateresource allocation for items such as base address and interrupt
level. After assigning these resources, the operating system enables the
device for operation.
Standard Banana
Jack Accessories
OR
Plastic Tip Cover
(Included with Probe Kit)

© National Instruments Corporation 3-1 DAQMeter DAQCard-4050 User Manual
Chapter
3
DMM Operation
This chapter describes how to use your DAQMeter DAQCard-4050 and
includes operation tips on taking voltage, resistance, diode, and current
readings.
Warm-up
Measurements taken with theDAQCard-4050 change with temperature.
These changes are calledthermal drifts or temperature coefficients. The
DAQCard-4050 temperature coefficient specifications are listed in the
Accuracy sections in Appendix A, Specifications. PCMCIA slots,
especially those in many notebook computers, can warm up a card
significantly above the ambient temperature. Therefore, measurements
made immediately after inserting the DAQCard-4050 or powering up
the computer can differ significantly from measurements made after the
DAQCard-4050 has fully warmed up.
To minimize the effects of thermal drift and ensure the specified
accuracies, let the DAQCard-4050 warm up for at least 30 seconds after
power-up before taking measurements. To maximize the relative
accuracy of measurements, take all measurements after the
DAQCard-4050 has had a chance to fully warm up in the computer,
about 15 minutes.
Choosing a Reading Rate
In all measurement ranges and modes of the DAQCard-4050, there
are three possible reading rates available for use—10, 50, and
60 readings/s. The reading rate is the rate at which a new measurement
is taken. In addition to the measurement speed, the selection of the
reading rate affects the filtering, and thus the noise level, of
measurements.

Chapter 3 DMM Operation
DAQMeter DAQCard-4050 User Manual 3-2
© National Instruments Corporation
In NI-DAQ, you set the reading rate directly. To optimize the
measurement accuracy and minimize the noise level, you should choose
a reading rate of 10 readings/s. If you are using the DAQCard-4050
Instrument Driver, select the resolution or the aperture time. Also
called the number of powerline cycles, aperture time is the period of
time over which a measurement is averaged. The setting of resolution
and aperture time for the DAQCard-4050 Instrument Driver are
discussed in the ni_dmm.hlp file on the instrument driver installation
diskette.
In practice, much of the noise encountered in measurements occurs
at harmonics (multiples) of the local power line frequency. The
DAQCard-4050 filters out noise at harmonics of its reading rate. A
reading rate of 50 readings/s filters noise at harmonics of 50 Hz, while
a reading rate of 60 readings/s filters noise at harmonics of 60 Hz. Since
both 50 Hz and 60 Hz are multiples of 10 Hz, choosing a sample rate of
10 reading per second will let the DAQCard-4050 filter out harmonics
of both 50 Hz and 60 Hz.
Measuring Voltages
Connect the test probes to voltage signals as shown in Figure 3-1. For
DC voltages, the HI (red) terminal is the positive terminal, and the LO
(black) terminal is negative. For AC voltages, positive and negative
terms are irrelevant.
The DAQCard-4050 is protected against damage from voltages within
±250 VDC or 250 Vrms in all ranges. You should never apply voltages
above these levels to the inputs.
Caution: To prevent possible safety hazards, the maximum voltage between either of
the inputs and the ground of the computer should never exceed ±250 VDC
or 250 Vrms.
Figure 3-1. Connecting Probes for Voltage Measurement
!
AC Voltage
Source
DC Voltage
Source
+
-
250 V
MAX.
LO
HI
250 V
MAX.
LO
HI