The Newsletter

An A.T.E. Solutions, Inc. Internet Publication
Volume 11 Number 5 March 1, 2007


Find any text on test. Search the topic below by typing a key phrase:

Search Now:

The Testability Director Version 3.2

Reach the thousands of test professionals we mail to. Sponsor The BestTest Newsletter and we will place your logo here.

Visit BestTest - A Test Community Web Site
Test Vendor Directory
Products/Services Directory
Test Dictionary
Test Events
Test Publications

Test related books
Test/Testability Software

How We Can Help
Test Requirements Analysis
Test Related Courses
ATE and Test Market Help
Design for Testability
Built-In Self Test

Links Worth a Click
Test sites of interest:

Cable Test Systems, Inc.
Chroma USA
Evaluation Engineering
International Test Conference
IPC - APEX Conference Organizers
Powell-Mucha Consulting, Inc.
Test & Measurement World

Want to trade links? We'll list yours here and you list ours at your site.
Test Vendors
We now have 2304 test vendors listed in the Test Vendor Directory. Check for accuracy.
The following companies have recently placed advertising with us:
A.H. Systems, Inc.
A.T.E. Solutions, Inc.
Capital Equipment Corp.
CEIBIS Cody Electronics
ESPEC North America
FTS Systems, Inc.
Ground Zero ElectroStatics
Intellitech Corporation
Invisar, Inc.
JTAG Technologies, Inc.
Madell Technology Corporation
Measurement Computing
Pickering Interfaces, Ltd.
ProbeStar, Inc.
QStar BE
Saelig Company Inc.
Tabor Electronics
Tecpel Co., Ltd.
Teradyne Assembly Test Division
Tiepie Engineering
VI Technology, Inc.
Wavecrest Corp.
WesTest Engineering Corp.
Yokogawa Corp. of America
Z World
A.T.E. Solutions, Inc.
   Consulting Services
   Consulting, Training and Books
   The Testability Director
   The Testability Director 3.2
Auriga Measurement Systems, LLC
   Microwave/Millimeter Wave Test Systems
Capital Equipment Corporation
Flynn Systems Corp.
   onTAP® Boundary Scan Software
Geotest Inc.
GOEPEL electronic GmbH
   OptiCon BasicLine
   SCANPLUS Board Grabber
ICS Electronics
Intellitech Corp.
   PT100 Parallel Tester
   PT100 Rack
   Scan-Ring-Linker & multi-PCB linker
JTAG Technologies, Inc.
   JT 3710/PXI
   JT 37x7 DataBlaster boundary-scan controllers
Meret Optical Communications
   ADS 53x DDS Synthesizer
Norvada, LLC
Professional Testing DBA Pro Test
   Environmental Testing
Quad Tech
   Guardian 1030S Multi-Purpose AC/DC/IR/SC Hipot Tes
Quantum Change, Inc.
   The TILE EMC Software
Reinhardt System und Messelectronic
   ATS-KMFT 670
Ricreations, Inc
   CleverScope CS328
   USB Explorer 200
   SMX2040 series
Static Solutions
   CT-8900 Combination Data Logger Tester
Symtx, Inc.
SyntheSys Research, Inc.
   BERTScope™ 12500A
Tabor Electronics
   Model 5200 Arbitrary Waveform Generator
   Test Equipment
TestEdge, Inc.
Testpro AS
   TP2101 Testsystem
The Test Connection Inc.
   In-Ciruit Test & Flying Probe Test
UltraTest International
Universal Synaptics
   Vanguard Express
WesTest Engineering
WesTest Engineering Corp.
   WesTest 2000
YESTech Inc.
   YTV series of AOI
Yokogawa Corp. of America
This Issue's Feature Articles

Specifying Data Acquisition May Be More Involved Than You Thought


Louis Y. Ungar, Editor, The BestTest Newsletter
User Instruction

You will be linked directly to the listings you select below after you have  logged in. If you are not logged in, go to 
If  you continue to have difficulties go to the posted copy of this Newsletter at the address on the very top of this page. 

Product/Service Focus

This issue's focus is Data Acquisition
You can view and add to our existing list of Test Products/Services, Test Literature, Test Definitions, Test Vendors, containing "Data Acquisition"

What's New in Test
  2/22/2007 MOSAID to Sell Memory Test Assets to Teradyne; Focused on Intellectual Property
  2/21/2007 CheckSum teams with Corelis to deliver boundary-scan test
  2/21/2007 DfR Solutions announces partnership with BQR
  2/16/2007 Agilent Technologies reports1Q 2007 results
  2/16/2007 Nanometrics revenue up year-over-year, but net loss grows
  2/16/2007 Test Educational Courses and Resources Web Tool Launched

Come to a One-Day Course

Cost Effective Tests Using ATE, DFT and BIST

by Louis Y. Ungar in New York, NY on April 11, 2007 

Magazine Articles
  2/27/2007 Test Goes Lean with Boundary Scan
  2/16/2007 Choose an oscilloscope with the right bandwidth
  2/16/2007 How to test EMC in semiconductors
  2/16/2007 NI: The future of test is virtual
Product Releases
  3/1/2007 Boundary Scan Platform SCANFLEX with new Controllers for highly complex PXI Systems
  2/27/2007 Agilent unrolls monitoring solutions for SIGTRAN
  2/27/2007 LitePoint Introduces Dedicated WiMAX One-Box Tester for Volume Manufacturing
  2/26/2007 Agilent, Innowireless offer mobile WiMAX test set
  2/23/2007 Agilent claims 'first' analyzers for IMS, UMA nets
  2/21/2007 Fixtureless testing joins the ScanINSPECT family flying probe tester
  2/21/2007 X-Tek announces new features for the Revolution X-ray inspection system
  2/20/2007 Agilent Introduces Fastest, Easiest Way to Bring Power of In-Circuit Test to Production Lines
  2/20/2007 Huntron Workstation Software 4.1 Update is released
  2/20/2007 In-Circuit Vectorless Test Technique with Network Parameter Measurement Technology
  2/21/2007 Google Says Diagnostics Don't Catch Many PC Drive Failures
  2/26/2007 IPC-7351A For Surface Mount Design and Land Pattern
  2/16/2007 Investment in JTAG standards development benefits entire industry
Web postings
  2/16/2007 How Military Testing Standards are Changing
White Papers
  2/28/2007 Top 10 Things to Consider when Selecting a Digitizer/Oscilloscope
Specifying Data Acquisition May Be More Involved Than You Thought
Louis Y. Ungar, Editor, The BestTest Newsletter

Data acquisition (DAQ) products are usually less expensive than other test equipment you may be using, but that is not a reflection of their simplicity.  As with other test and measuring equipment the parameters you measure are of greater value than the equipment (or should be) and it is from the perspective of the unit under test (UUT) that you should evaluate the Best DAQ for you.

National Instruments in a glossary format has done a very nice job of defining many of the terminology we use in specifying DAQs.  We used that document to highlight the points we make here and readers are urged to consult that document (or our own BestTest Dictionary) to get a better handle on some of the technical terms.

Data Acquisition usually collects analog inputs (sometimes digital inputs as well) and converts them to digital data that can be readily processed by a computer or controller, which is often a part of an automatic test equipment (ATE) set up.  (DAQs with analog outputs also exist.)

Input Signal Characteristics

With analog input you will need to specify the number of analog channels you will need, whether they are single-ended, differential or pseudodifferential (with common grounds that are not connected to the computer ground.)

You should select the type of analog to digital converter (ADC) that is appropriate for your signals – successive approximation, flash, half-flash, integrating or delta-sigma modulation.  You need to pay special attention to its resolution, its maximum sampling rate, input signal ranges, input coupling, maximum voltages, and its overvoltage protection.

Once the ADC converts the signal, handling the data is also crucial.  Usually a buffer is used to collect the signals and the size of this buffer determines the maximum sampling rate.  Data transfer can be accomplished in a number of ways – direct memory access (DMA), interrupts, and programmed I/O.  The last two require CPU intervention and compromise speed.  With DMA you generally maximize transfer rates, but there are still several modes to choose from.  Single-mode transfers involve one data value transfer per request and may not be sufficiently fast.  Block and demand transfer modes increase transfer rates.  For block mode transfers the DMA controller performs the entire DMA sequence at the fastest possible rate in response to a single DMA request.  For demand mode transfers, the DMA controller performs DMA transfers as fast as possible as long as the DMA request is asserted.

The ADC process is inherently compromised by inaccuracies and errors that should be specified for the DAQ you are considering.  Relative accuracy measures the nonlinear errors associated with a DAQ system in terms of least significant bits (LSBs).  Nonlinearity measures the percent of full scale range of the worst-case deviation from the ideal transfer function, a straight line.  There is also a specification for one or more types of offset errors.  There is also gain error to consider, in which the error increases as the gain increases.  Since the ADC contains amplifiers, the amplifier characteristics should also be considered.  These include, input and output impedance, bias and offset current and common mode rejection ratio (CMRR).

Consider the dynamic characteristics as well.  For example, the bandwidth frequency range and the –3 dB cut-off are extremely important to match with the signal you expect to acquire.  The dynamic range, the total harmonic distortion, amplitude flatness, phase linearity, interchannel phase, intermodulation distortion overload recovery time and crosstalk need to match your requirements.

Filter types indicate the purpose the filter serves.  For example, simple single-pole RC filters are for noise rejection, while more sophisticated hardware and digital FIR filters are suitable for antialiasing filters.  You should take into account that the cut-off frequency (-3 dB) attenuates power, and stationary filters such as RC filters express cut-off frequency in Hz while digital antialiasing filters that move with the sampling rate will express cut-off frequency in terms of the sample rate.  You should look for the following specifications:  Maximum external clock frequency, passband ripple, stopband attenuation, attenuation rate, normal mode rejection (NMR) and signal delay.

The ADC also has sample-and-hold (S/H) characteristics.  The acquisition time is the time required for the S/H amplifiers to track to the correct voltage level of the input when coming out of the hold mode.  This requires that you consider the hold-mode settling time, the droop rate, the interchannel and intermodule skew, the aperture delay time and jitter, and the hold step.

As temperature and other environmental consideration may come into play, you may need to take into account stability specifications.  These include, recommended warm-up time, offset temperature coefficient, gain temperature coefficient, long-term stability and of course, calibration references.

Output Signal Characteristics

Many of the same characteristics apply to analog outputs as it does to analog inputs.  

For Digital I/O some other characteristics need to be considered.  Compatibility (TTL or CMOS), power-on state (logic low vs. logic high), digital logic levels (what voltage or current constitutes a low or a high), Darlington Drive Output Current, Common- Mode Isolation, Common –Mode Transient Rejection, transfer rate, propagation delay, and handshaking protocols.

Digital Relay Characteristics

DAQs use relays to switch the various channels.  Relay types include single-pole double-throw (SPDT), latching or nonlatching.  SPDT relays, also called Form C, can switch one channel from a common (COM) terminal between a normally open (NO) and normally closed (NC) terminal.  Latching relays maintain their latest state even when powered down, while nonlatching relays return to their normally closed state at power down.

Specifications to look for include maximum input voltage, maximum switching voltage, maximum and minimum switching capacity, ON resistance, output capacitance, leakage current, contact material, expected life, thermal offset, maximum operating speed, relay set and reset times, as well as relay operate and release times.

Timing I/O Characteristics

Many of the parameters for Timing I/O are similar to those for Digital I/O, such as logic levels for input and output voltages and currents.  There are some parameters, however, that are more specific to timing considerations.

Base clock (on-board counter timer) availability and accuracy should be considered.  Maximum source frequency, minimum source pulse duration and minimum gate pulse duration parameters should be specified.

Also, as in Digital I/Os the data transfer mechanisms, including the availability of DMA transfer is an important consideration.


You should understand both analog and digital triggers when you select a DAQ.  For analog, the trigger source, its level, its slope, and its resolution should be quantified.  You should know its hysteresis, bandwidth, coupling and the type of protection method it uses.

For digital triggering you need to consider the digital voltage level compatibility, responses to an edge or to a voltage level and the pulse width that can activate the digital trigger.

Excitation Channels

The number of excitation channels that a DAQ uses is an important selection criterion.  The bridge type sensors that can be used (quarter, half or full) and the bridge completion (resistors) required is a factor to consider.  The voltage level of excitation channels, their current drive, voltage drift, current level, maximum load resistance and current drift should be specified.  There should also be cold-junction reference for output voltage, accuracy and repeatability.

Digital Signal Processor (DSP)

The digital signal processor on board the DAQ is an important criterion.  Is the DSP chip computation performance optimized for math operations common to spectral analysis, such as Fast Fourier Transform or convolution?  Do they feature parallel multiply operations and can they handle DMA transfers and interrupt requests?  The DSP clock speed, instruction rate and floating point rate should be considered.

The size of the memory located in the DSP as well as its ability to perform dual-ported and dual access operations is also a factor.

DMA controller access, maximum transfer rate and number of channels should be specified.  What types of interrupts does it use?  What is the time required for transfer of 1 Kwords of data?

DAQ in System Integration

National Instruments uses the Real Time System Integration (RTSI) bus, but other system interfaces can be used for DAQ from other vendors.  The system integrators will want to know a number of specifications to get the DAQ into a test system.

Electrical specification should provide for trigger lines, clock skew, DMA channels, serial links and their transfer rates, bus interfaces, and power requirements.  The physical specifications should include dimensions, I/O connector types, PCMCIA card types if used.  There should also be environmental specifications, including operating temperature, storage temperature and relative humidity.


For a number of choices of data acquisition, you can visit The BestTest Products and Services Directory.  Low price and high performance are desirable traits of DAQs. As a buyer, however, you have to be certain that it serves the purpose of testing your UUT.  To make sure it does, you need to ask the right questions and this article alerts you to the specifications you should be looking for.

Next Issue's Product/Service Focus
In our next issue of Product/Service Focus we will cover Measuring Equipment/Oscilloscopes. You can add or upgrade a listing before the next issue comes out.

If you would like to include an exclusive article on how to best select Measuring Equipment/Oscilloscopes, please contact

  • If your friend forwarded this newsletter to you, please register as a member and receive The BestTest Newsletter -- absolutely free!
  • If you wish to update your news preferences or cancel the subscription, please unsubscribe.
  • If you have any questions, please email
See an Index of Past and Upcoming Issues of The BestTest Newsletter

Email The BestTest Newsletter to a Friend whose email is
Online Bookstore

Get the widest selection of test related books and software at the BestTest Online Store.


Reach the thousands of test professionals we mail to.
Place Ad here.



   Cost Effective Tests Using ATE, DFT and BIST
9/17 - 9/21
   AutoTestCon 2007
3/5 - 3/7
   International Test Synthesis Workshop (ITSW 2007)
3/6 - 3/8
   Fundamentals of Random Vibration and Shock Testing, HALT, ESS, HASS
3/11 - 3/14
   IEEE Latin-American Test Workshop (LATW 2007)
3/11 - 3/15
   IEEE Wireless Communications & Networking Conference (WCNC 2007)
3/20 - 3/22
   Aviation Industry Expo
3/20 - 3/21
   Amircan Contract Manufacturers Conference
3/21 - 3/23
   Electronica and Productronica China
3/27 - 3/29
   Aerospace Testing Expo 2007 - Europe
4/1 - 4/5
   Embedded Systems Conference
4/4 - 4/6
4/10 - 4/12
   Fundamentals of Random Vibration and Shock Testing, HALT, ESS, HASS
4/11 - 4/13
   IEEE Workshop on Design and Diagnostics of Electronic Circuits and Systems (DDECS 2007)
4/15 - 4/19
   International Reliability Physics Symposium
4/16 - 4/20
   International Conference on Data Engineering (ICDE 2007)
4/16 - 4/20
   Design Automation and Test in Europe (DATE)
   Diagnostic Services in Network-on-Chips
4/24 - 4/27
   Nepcon China 2007
4/24 - 4/26
4/29 - 5/2
   ESTECH 2007
4/30 - 5/3
   International Instrumentation Symposium
5/6 - 5/10
5/8 - 5/10
   Automotive Testing Expo Europe
5/10 - 5/11
   IEEE International Workshop on Open Source Test Technology Tools
5/14 - 5/17
   International Electrostatic Discharge Workshop
5/15 - 5/17
5/20 - 5/24
   12th IEEE European Test Symposium (ETS'07)
5/23 - 5/24
   International Workshop on Silicon Debug and Diagnosis (SDD07)
5/24 - 5/25
   European Board Test Workshop (EBTW)
6/3 - 6/8
   IEEE MTT-S/International Microwave Symposium
6/3 - 6/6
   Semiconductor Wafer Test Workshop (SWTW 2007)
6/4 - 6/8
   44th Design Automation Conference
6/12 - 6/14
   Fundamentals of Random Vibration and Shock Testing, HALT, ESS, HASS
6/18 - 6/20
   International Mixed-Signals Testing Workshop (IMSTW'07)
6/18 - 6/20
   International GHz/Gbps Test Workshop (GTW 07)
6/18 - 6/21
   International Metrology Congress
6/19 - 6/22
   Nepcon Malaysia
6/20 - 6/21
   Successful Lead-Free RoHS Strategies Conference – Do it Right, Do it Now
6/20 - 6/22
   Fundamentals of Random Vibration and Shock Testing, HALT, ESS, HASS
6/21 - 6/24
   Nepcon Thailand
7/8 - 7/13
   EMC Symposium
7/9 - 7/11
   International On-Line Testing Symposium (IOLTS'07)
7/10 - 7/12
   Fundamentals of Random Vibration and Shock Testing, HALT, ESS, HASS
7/16 - 7/20
   Coordinate Metrology Systems Conference (CMSC)
8/7 - 8/9
   National Instruments' NI Week
8/21 - 8/23
   International Military & Aerospace / Avionics COTS Conference
8/28 - 8/31
   NEPCON South China
9/9 - 9/12
   International KGD (Known Good Die) Packaging & Test Workshop
9/19 - 9/21
   International Exhibition on Test Equipment 2007
9/21 - 9/23
   IEEE Wireless Communications, Networking and Mobile Computing (WiCOM2007)
9/26 - 9/28
   International Symposium on Integrated Circuits
9/26 - 9/28
   International Symposium on Defect and Fault Tolerance in VLSI Systems (DFT'07)
10/7 - 10/11
   SMTA International 2007
10/22 - 10/23
   IEEE Product Safety Engineering Society Symposium
10/23 - 10/25
   International Test Conference 2007
10/24 - 10/26
   Automotive Testing Expo North America
10/30 - 10/31
   NEPCON East
11/4 - 11/9
   Antenna Measurement Techniques Association (AMTA) Symposium
11/6 - 11/8
   Aerospace Testing Expo 2007 - North America
11/6 - 11/8
   Bohai Electronics Week
11/6 - 11/8
11/11 - 11/13
   National Quality Education Conference
11/13 - 11/16
New Definitions
New terms added to the Test Definition section:
AC Coupling Low-Frequency Cut-Off (–3 dB)
Acquisition Time
Amplitude Flatness
Aperture Delay Time
Aperture Jitter
Attenuation Rate
Common Mode Isolation
Common Mode Transient Rejection
Darlington Drive Output Current
Data Transfers
Droop Rate
Gain Error
Hold Mode Settling Time
Hold Step
We now have 2394 test terms in our Test Definition section.

Share your definitions with the test community.