Testing moves to 'Easy Street'

DN Staff

March 25, 1996

13 Min Read
Testing moves to 'Easy Street'

Testing comprises an integral part of any design, but test engineers often find themselves out on the street following the first wave of corporate layoffs or "downsizing." Most smaller firms don't have the luxury of employing specialized test engineers. So, as more design engineers take on testing, test-instrument vendors know that their equipment must become easier to use.

Test equipment also needs to keep pushing the cutting edge as such high-speed, high-bandwidth technologies as computers and communications drive the U.S., European, and Japanese economies.

Those are just a few of the lessons from a special Design News tour of test and measurement companies. Among other insights gained from the tour:

* More and more instruments are gaining computer interfaces. These ports let your computer control the test equipment, and let you download measurements for further analysis.

* Integration of measurement functions has decreased the number of instruments on an engineer's bench. For example, digital multimeters (DMMs) contain frequency counters, and scopes contain DMMs and spec-trum analyzers.

* Instruments are becoming smaller and easier to use. Lots of research goes into designing front panels that are intuitive, but there's a fine line between having too many keys and having so few that users get lost wading through layers of menus.

* "Help" has evolved into "Information." No one has the time or inclination to read a manual, so many companies store the manual in the scope or meter's memory. Also, nobody wants to press the "Help" key with a customer looking over his or her shoulder. So look for an "Information" key instead on the newest models.

The U.S. dominates the worldwide test and measurement market, which grew 10% last year, according to market research firm Prime Data. No one region can claim the top spot for test-equipment companies, so on this tour I cut a swath through the U.S.--from New York to Washington state--to uncover the latest test-equipment designs offered by five leading firms.

These scopes never forget
LeCroy, Chestnut Ridge, NY, got its start making measurement equipment for high-energy-physics research in 1964. In fact, it has a design and manufacturing facility just outside CERN (Centre Europeen pour la Recherche Nucl+ire) near Geneva, Switzerland. This high-end equipment acquires data from an event where one subatomic particle interacts with another subatomic particle at the speed of light.

"The job was to track the multiple electronically charged particles that were created by such an event," says Mike Lauterbach, LeCroy's director of product management and a former high-energy physicist. "So the job of LeCroy from its infancy was to measure the smallest, fastest electronic signals as precisely as possible in time and voltage."

Today, LeCroy is the leader in high-energy-physics electronics, and has leveraged that technology to design high-performance digital storage oscilloscopes (DSOs). DSOs capture electronic signals, convert them to digital form, display them, and perform sophisticated measurements and analyses.

The 9374L, the company's latest DSO, features: 1-GHz bandwidth, 2-giga sam-ple/sec sampling, storage for waveforms of up to 8 million points, four channels, 2 PCMCIA slots for flash memory and a hard-disk drive, and an integrated thermal printer that can print yards-long waveforms. With the new extended-memory option, this scope can pack 64 Mbytes of RAM for processing long waveforms, doing high-speed signal processing, and upping the trace-update rate.

The amount of memory an engineer needs depends on the length of the waveforms to be processed. For example, performing a simple function--such as a log--on a 1 million-point waveform requires 4 Mbytes; doing an FFT (Fast Fourier Transform) on the same signal takes 8 Mbytes. Other calculations the extended-memory option enables include: integration, differentation, square root, and six selectable digital filters.

Another feature unique to LeCroy scopes is the exclusion trigger. The toughest electronic problem to debug is one that's intermittent--especially if the shape of the failing signal changes characteristics each time the failure occurs. You don't know when to trigger the scope because the failure is irregularly spaced in time, and you don't know what shape of signal to trigger on because the failure doesn't always have the same characteristics.

What you do know is the shape or period of the normal pulses. Using the exclusion trigger, users specify that information so the scope can ignore normal-shaped signals and trigger only on abnormal events. By avoiding triggering on normally shaped signals, the 9374L actively looks for circuit failure nearly 100% of the time.

Meter gets to the 'source' of problems
Celebrating its 50th anniversary this year, Keithley Instruments, Cleveland, OH, specializes in precision equipment for making extremely low-level electrical measurements. Overseas sales account for 50% of the company's annual revenue. Certain to make these sales figures grow, the Test Instrumentation Group just achieved an integration first by combining a DMM with precision current and voltage sources.

Compared with systems you might cobble together, the new Model 2400 Digital SourceMeter takes half the time to set up and program, uses a quarter of the typical rack space, and, at $3,495, costs less. It's also easier to use than separate instruments because Keithley has already taken care of instrument synchronization and wiring.

Why use a source and a meter together? Typically, meters don't tell you what stimulus voltage or current they're using to make measurements. Even if they did, the voltage or current could move around. The SourceMeter lets you make, for example, resistance measurements at a precise voltage.

The design team essentially re-engineered Keithley's SMU (Source Measurement Unit), which was targeted for semiconductor applications. Production en- gineers adopted the SMU for component testing--an application Keithley didn't foresee and design the unit for.

The original SMU has fans, electromechanical relays, and other components that were prone to failure in dusty, hostile production environments. "We eliminated mechanical relays for solid-state range switching and used only passive cooling in the Model 2400," says Project Manager Chuck A. Cimino, III. The team also simplified the front panel and made the user interface as DMM-like as possible.

SourceMeter applications include:
* High-speed production testing of such components as resistors, resistor networks, diodes, LED displays, thermistors, resettable fuses, and portable battery-powered devices and components.
* Complete dc electrical characterization in test development or off-line analysis. Measurements include breakdown voltage, leakage current, resistance at specified voltage or current, power dissipation, and current consumption.
* Precision voltage and current sourcing in production testing and R&D.
You can make these measurements at speeds of 1,000 readings/sec at 4.50 digits over the IEEE-488 (GPIB) bus. And a Source Memory List eliminates the bus traffic usually required to configure multiple tests by saving up to 100 test definitions in memory.

"The 2400 is really the next evolution of the DMM," says Marketing Manager Mark Hoersten. The only thing DMMs do that this unit doesn't is make ac measurements. But, says Hoersten, that's in the works.

Parallel processors speed scope
Hewlett-Packard, Electronic Measurements Div., Loveland, CO, has a key motto: "Within budget, without compromise." The Test and Measurement Division has met the challenge. The new HP 54615B DSO sports a 1-gigasample/sec sampling rate, 500-MHz bandwidth, 1-nanosecond peak detect--and a very reasonable $5,595 price tag.

"A scope is the only way for an electrical engineer to realize a design," says Mark Lombardi, oscilloscope product marketing manager. "You can't see whether your circuit is generating the signals you want it to without using one."

Because HP only makes digital scopes, HP designers at the division use analog-scope strengths as a guide for improving their DSO designs. For example, one of those strengths is minimal "dead time," the time between waveforms displayed on screen. An analog scope's dead time is the time the electron beam requires to bounce back to the left side of the CRT to start tracing another signal. A digital scope is "dead" between the time it acquires a signal, processes it, then displays it. The digitizing step can eat up lots of time.

To address this problem, HP designers add dedicated math processors devoted to processing signals. That way, other oscilloscope functions, such as monitoring the front-panel controls, don't distract the display function of the scope, which would increase dead time.

The new 54615B DSO has three processors working in parallel, instead of the typical single processor doing all the work serially. This lets the scope capture more incoming signals, respond instantly to commands, and immediately show changes in the setup or signal.

Customer research HP did during the development of the 54615B showed that, because sample rates drop when DSOs operate at slow sweep speeds, engineers felt that digital scopes take too few samples and might miss important data. (Analog scopes are directly driven by a signal--they don't go through the digitizing step, so nothing gets by them.) Many engineers also said that high-performance digital scopes were too difficult to use.

"We addressed these issues with a high-performance, intuitive DSO that combines a fast sampling rate with high bandwidth and a peak detect that captures 1-nanosecond events at any sweep speed," says Lombardi. "Engineers can trust what they see on the scope's display." The familiar analog interface adds ease of use.

Banner specs, such as sampling rate and bandwidth, are typically those on the front panel of a scope. Some scopes are optimized for one or more banner spec, but HP concentrates on general-purpose scopes and pushing all the specs.

Many features that might be critical for a specific design project might not even make a scope's data sheet, warns Lombardi. He suggests that anyone considering investing in a scope--or any significant piece of test equipment--ask for a demo first or try it out. "Since a spec sheet never tells the whole story," Lombardi adds, "you must take the application into account."

Ease of use is key
Fluke Corp., Everett, WA, makes everything from meters to digital scopes and data-acquisition modules to LAN test tools. Its acquisition of the test and measurement business of Dutch-based Philips Electronics in 1993 also makes it a multinational company.

One of Fluke's latest designs, the 860 Series Graphical Multimeters (GMMs), puts an oscilloscope in the palm of your hand. Designed for rugged environments, the GMMs let users choose among analog, digital, and graphical displays. Because of this versatility, the units have won many industry awards, including the Industrial Designers Society of America's "Industrial Design Excellence Award."

"You don't have to be really scope-familiar to use the 860," claims Cliff Asbill, Fluke product marketing manager. The all-digital scope lets users view a waveform to see if there's a problem that requires a full-featured DSO. Because the unit is portable and tough, it's a favorite with engineers at the "Big Three" automakers, Fluke says.

The GMM is especially good for electromechanical applications where its 1-MHz bandwidth will suffice. For example, Wagner Spray Technology, Plymouth, MN, used a GMM in the design of a paint sprayer. Test engineers discovered during life-cycle testing that the contacts on the pressure switches repeatedly burned out. At first, they thought the problem was mechanical, but the GMM showed that large in-rush current spikes from the equipment's ac motor caused arcing across the contacts. Faster, snap-open switches solved the problem.

Other GMM features include: an optically isolated port for connecting the unit to a computer, MS-DOS and Windows software, a 120-point waveform display, memory for storing three waveforms and multiple test configurations, and an "Information" button.

Another Fluke product that combines a DSO and a meter is the ScopeMeter. Applications Engineer Dave Pereles describes it as "more of a scope than a meter. It has a 100-MHz bandwidth, compared with a GMM's 1-MHz spec, but the DMM portion is less accurate."

Fluke designed the product for engineers who need the horsepower of a scope, but don't have much expertise using them. In fact, the unit looks a lot like the GMM and operates more like a meter than a traditional scope. Designers did lots of customer research to develop a friendly user interface. "We discovered that you're better off with buttons than menus," says Pereles. "One logical classification deserves its own button."

The battery-powered ScopeMeters can run up to four hours on one charge. Users can directly access a pop-up menu of 30 common measurements. For more complex signal measurements, the continuous autoset function eliminates front-panel reconfiguring as users move from one test point to the next.

Fluke's latest ScopeMeter--the Model 105--lets users select between English and one other language. Choices include French, German, Spanish, and Dutch. A Japanese version is in the works. Although the front panel is in English regardless of the second language, the keypads have become icons for most non-English speaking users.

Also combining instruments is Fluke's CombiScope oscilloscope series. These units employ a DSO and an analog scope, giving users the best of both worlds.

Digital scope rivals analog speed
Headquartered in Wilsonville, OR, Tektronix is also celebrating its 50th anniversary. Its first product: an analog oscilloscope. Now, business units include color-printing and video and networking divisions, but the test and measurement business accounts for 50% of total sales.

Test products range from logic analyzers and oscilloscopes to fiber-optic cable testers and embedded systems debugging tools. Tek's oscilloscopes command a 46% share of the worldwide scope market.

Despite this sterling performance, the company's goal is to replace analog scopes with DSOs.

One reason Tek is confident about abandoning analog scopes: its recently released InstaVu(TM) signal acquisition technology. The technology has become a standard feature of its new TDS 700A and TDS 500B series DSOs. InstaVu lets users capture up to 400,000 waveforms/sec, making these new digital scopes as fast as the world's fastest analog scopes, claim company officials.

"Many scope users have stayed with analog because they lack confidence in conventional DSOs' acquisition performance," notes Rick Wills, vice president and general manager of the Instruments Business Unit. DSOs typically capture 100 to 150 waveforms/sec.

InstaVu combines high-speed acquisition memory with high-speed display rasterization to increase acquisition performance, ensuring real-time display of signal changes. In short, InstaVu minimizes DSO dead time and overwrites "layers" of waveforms. This gives designers a better chance of pinpointing unpredictable, rapidly changing signals--infrequent glitches, metastable behavior, and time jitter--than if they were using conventional analog or digital scopes or specialized triggering.

Other TDS 700A and TDS 500B specs include: sample rates up to 500 megasamples/second on all channels, or up to 4 gigasamples/sec on one channel; bandwidths of 500 MHz to 1 GHz; monochrome or color displays; 250k- to 500k-point record lengths; and 1-nanosecond peak detect.

One engineer, Charles Homes, reports he saved days of troubleshooting effort by using the TDS 744A's InstaVu mode. Homes works for Quiktrak Technologies Pty. Ltd., Bedford Park, South Australia, a subsidiary of British Aerospace Australia. The firm develops and supplies wireless vehicle tracking, security, and two-way messaging systems.

"Digital scopes are great for their range of triggering modes and display options," explains Homes. "Of course, unless you know what you're looking for and choose the appropriate trigger, you can miss things on a digital scope that you may catch with an analog scope. The TDS 744A lets me see signal behaviors in InstaVu mode that previously would be visible only with a good analog scope."

You can reach the following companies mentioned in this feature on the World Wide Web.

Fluke Corp. http://www.fluke .com
Hewlett-Packard Co. http://www.hp.com
Keithley Instruments Inc. http://www.keithley.com
LeCroy Corp. http://www.lecroy.com
Tektronix Inc. http://www.tek.com/measurement

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