By Hans Toorens
Toorens is product marketing manager at Philips T&M Group, John Fluke Mfg. Co.
Oscilloscopes are hardly a new product. To many users, they are not considered an exciting product, either, just a tool to be taken for granted. Recent changes presage an exciting future for oscilloscopes, a future that reaches to new product features and to many new markets.
"Looking glass" tools
The earliest analog oscilloscopes were primarily observation, "looking glass" tools, not measurement tools.
They lacked calibrated vertical amplifiers and time bases, and they lacked trigger circuits, so viewing non repetitive events was impossible.
Early scopes were lacking as observation tools. There wasn't a permanent record of their display. Repetitive events could be shown, but single occurrence or low-repetition events could not be captured, except with a camera, making the operation complex and clumsy.
Special CRTs, called storage displays, later solved these observation and re cording problems, but they lacked brightness and were expensive. More accurate vertical and horizontal systems eventually arrived, as did trigger-control circuitry, making calibrated time bases feasible for the first time. Further refinements included expanded vertical and horizontal displays, differential vertical amplifiers, dual time bases, and more trigger refinements.
Yet the oscilloscope still seemed to be primarily used as an observation tool.
Even with calibrated voltage and time systems, errors crept in.
DSOs
Today, we have digital storage oscilloscopes (DSOs) - the first to replace analog storage scopes. Early DSOs were too slow for serious electronic tests and were used for mechanical, medical and other "slow" applications. Unlike non storage or CRT storage scopes, DSOs do not depend on the CRT as part of the measurement system.
It's a fact that the DSO has been a boon to measurement technology. But using DSOs in place of non-storage or display-storage scopes has required some adjustment for users.
DSOs are speeding up, too, with fast analog-to-digital (A/D) converters and charge-coupled devices (CCDs) for economical high-speed capture. With these refinements, DSOs became part of real electronics speed and applications.
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Modern DSOs not only display the waveform of a signal, but the microcomputer circuitry also calculates and displays such parameters as frequency, period, amplitude and more.
DSOs and analog oscilloscopes both display electronic signals, but the DSO also stores signals. performs calculations to determine and display waveform parameters, and transmits data to a computer to be saved on disk.
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Before you buy a scope ...
Perhaps this article has renewed your interest in purchasing a new oscilloscope.
The right scope, like any tool, will make your job easier. Many scopes offer powerful features, and their advertisements make them seem indispensable for any use. So how do you make the right choice? Here are some suggestions:
• Buy only what you need. We've spent a lot of time talking about DSOs, and we do believe they will become the predominant measurement tool of the '90s. However, many of you may not need the power of a DSO. Their cost is usually more than that of a non-storage scope. You know best what you need for your job.
Don't be caught in the "I need the best scope possible" trap. If your job is well defined with boundaries, buy specifically what you need. If your job is full of "what ifs," such as in engineering, take advantage of more power in modern DSOs.
• Make sure you're getting current technology. Even with DSOs, there are products on the market that rely on outdated circuitry. State-of-the-art DSOs have CCD acquisition systems, microprocessor control, and automatic setting capability. Does the one you're considering? If you are uncertain, buy a combi-scope, combining the convenience of the trusted analog scope with the power of a new DSO.
• Buy from someone you trust. What is the reputation of the manufacturer, distributor or dealer? What have been your experiences with other products with that nameplate? Does the product have a good warranty? Most high-quality products to day offer 3-year warranties. You shouldn't have to pay extra for this coverage.
• Attend seminars and demonstrations.
Many manufacturers offer free seminars to acquaint potential customers with their products. Ask your salesperson when the next seminar will be presented in your area. Ask for one-on-one demos also, especially if the manufacturer doesn't offer a seminar.
• Request videotapes, a loaner scope and lots of literature. Most brand-name manufacturers have introductory videos, a pool of demo instruments for short-term loan, and application guides. All of these can show you what the product can (and can't) do.
• Find out how the product will be sup ported after you buy it. Is there local applications support or a toll-free number to call when you have a question? The best product in the world won't do you much good if you can't get your problems solved and your questions answered.
• Find out about in-warranty and out-of warranty repair policies. We mentioned earlier that a 3-year warranty is typical for today's oscilloscopes, but you need to know exactly how the manufacturer supports that warranty. Do you get an immediate loaner scope if yours breaks? Or a replacement? Where will your product be repaired? How long does it take? Who pays shipping? Get it in writing.
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Today's scopes
As DSO development continues, de sign experience and technology improvements continue to make products faster and more affordable.
Several technological breakthroughs have dramatically affected the value of oscilloscopes. One such development has been the use of CCDs in the digital storage acquisition system. Before CCDs, digital storage relied on high speed A/D converters and memory.
A/D converters were typically one of two types: flash converters, which could digitize high-speed, single-shot events but were expensive; and successive approximation converters, which were less expensive but couldn't capture high speed events.
The CCD is an analog storage array.
Modern DSOs can capture high-speed events in real time using CCDs, then route the captured information to be digitized with low-cost A/D converters.
Another important innovation has been the widespread use of microprocessors in oscilloscopes. One advantage of a modern microprocessor-driven scope is its cold-switched front-panel controls. Cold switching means that complex, failure-prone electromechanical devices, such as attenuator and time base switches, have been replaced by microprocessor-controlled, sealed switching arrangements (reed relays and solid-state switches), so switch failures and worn or dirty contacts are a thing of the past. The introduction of micro processor power takes full advantage of cold switching. More microprocessor power allows DSOs to calculate results never before possible with any scope: rms, risetime, etc.
The front-panel switches are low current, long-life units, suitable for use in harsh environments, making the DSO ideal for field service, where it is constantly transported and exposed to weather and dust. The modern scope can also be controlled electronically over an IEEE or RS-232 interface bus, making remote servicing more practical.
Another new product - the combi scope - combines both analog and dig ital storage oscilloscope technology in a single package. Combi-scopes are more affordable; they handle both modes; and they're comfortable to use. Analog oscilloscopes are considered a mature product, but DSOs are only beginning to mature. Users no longer need to treat DSOs as an oddity or a luxury. More important, users are becoming comfortable with DSOs. In the process, they are finding many new uses for them.
Today, two trends exist: The overall scope market is expanding and DSO sales are increasing at 20% a year; and the non-storage scope market is shrinking.
DSOs have replaced display (CRT) storage products almost completely, and they are taking over traditional non storage markets. In particular, portable scopes aimed at service markets are dominated by DSOs.
One likely reason is that the DSO is regarded as a diagnostic test and measurement tool. Modern DSOs contain internal storage for multiple waveforms, thanks to low-cost memory. Many DSOs contain multiple memories, internal measurements, and stored front panel settings. These features aid troubleshooting. Readouts provide measurement results and front-panel settings.
Many modern DSOs have a feature that allows the scope to automatically find optimum settings, depending on signal conditions. This time-saving tool eliminates the distraction of changing settings when you are moving between test points. This allows the user to concentrate on the test-point signal, its appraisal and solution of the problem.
Intelligent scopes can now make key measurements and comparisons. Volt age peaks, means and rms values are calculated and displayed. Also, pulse parameters, such as rise- and fall-times, can be calculated. Signal frequency or period are evaluated as well, even for single events.
With oscilloscopes getting smarter and smarter, users can concentrate on test results, not scope settings and calculations to get those results. One danger of the smarter scope, unfortunately, is that as users gain more "what" information, they may lose sight of the "how" of test and measurement. A scope that thinks can lead to a user who doesn't.
The oscilloscope of the future Now, let's look into the future, based on experience, current trends, "hot" technologies, and a lot of comments from oscilloscope users.
Fiber optics have begun to replace electrical cable as a signal medium, not only in long-distance tele-communications, but within local area networks (LANs). In some cases, high-frequency signals are routed within instruments via fiber-optic cables because optical cables don't generate electrical or magnetic radiation and are not susceptible to this radiation.
Fiber optics also are generally physically smaller than their electrical counterparts. As frequency response of optical components continue to improve, so will the popularity of fiber optics.
Observing and measuring signals in fiber-optic cables requires a special interface or an optical, rather than electrical, input connector. Future scopes may have optical input connectors built in.
Another feature of future scopes will be the capability to share information over long distances. Troubleshooting in the field will get easier because the service technician will be able to send and receive waveforms over long-distance phone lines.
In many cases, a waveform is a "sig nature" of a specific failure mode, and a large database of these failure-mode signatures can be stored on a central computer system for all service technicians to use for comparison.
It used to be that new technology was concentrated in product design areas.
Today, and into tomorrow, the focus is high-technology manufacturing. For ex ample, more production lines will be controlled by computers linked to sophisticated sensors.
Already, the automotive industry makes extensive use of robotics. Automobile manufacturing also takes ad vantage of sophisticated laser optics for quality-control measurements.
Mass transportation technologies, such as linear-motor trains, continue to emerge. Control of these systems is extremely complex.
Many of today's commonplace hospital diagnostic equipment didn't even exist 10 years ago. This trend is sure to continue, with state-of-the-art electronics in hospitals and doctors' offices.
Home entertainment electronics now comes in sophisticated systems, rather than discrete, non-related components.
The trend continues at an increasing rate, especially with the advent of CDs, VCRs and HDTV. These are just a few examples of high technology electronics in what used to be either non-electronic or low technology areas. Today's home can have a dozen or more microprocessors in it, plus three or four more in the family automobile. Anyone who services anything will probably need some sort of diagnostic tool for microprocessor controlled electronics in the future.
Many of these tools will be DSOs.
With all of this new technology coming, better trained engineers and technicians are needed. Unfortunately, state of-the-art test equipment is expensive, and schools always operate on shoe string budgets. To help close the training gap, many companies are getting more involved with engineering and technical schools by donating test equipment.
Once real-world, up-to-date test equipment, such as DSOs, are more readily available, new engineers and technicians will spend less time learning how to use their tools and more time improving their skills.
On-the-job training time also will continue to increase. Already, there is a trend toward much longer on-the-job training cycles for service technicians.
This is most evident with high-tech products.
Becoming properly trained for the job will mean learning the products to be serviced, the tools to service them, and the methods for using the tools. Service technicians must not refuse to up date their servicing methods.
The scope of tomorrow As you've probably guessed by now, the oscilloscope of tomorrow will be a digital scope. In some ways, it will be an extension of today's digital scope: more intelligence, more memory, more capability, more ms/$, more powerful and more portable.
We've seen a tremendous increase in microprocessor computing power just in the past few years. That computing ability will increase in ability and speed, be come cheaper, and consume less power in the future. Digital scopes will benefit greatly. Complex measurement and analysis of stored waveforms will be possible with even low-cost DSOs.
There will be more measurements and there will be more waveforms to measure. Memory cost-per-bit will continue to fall dramatically. Low-power, non-volatile memories will be common place in all portable digital oscilloscopes.
Test electronics will be much different than those in use today. Many of to day's troubleshooting tools will be replaced by a single, intelligent DSO used by a highly trained professional to help properly diagnose the high-tech world of tomorrow.
Also see: Oscilloscope--special report