How happy were you with your scope’s performance the last time you had to troubleshoot a complex problem? Did it have enough channels, speed, and triggering capability, and was it easy to use? Or, did you have to struggle a little and maybe weren’t able to make that last, really interesting measurement? Were you frustrated, delighted, or somewhere in between?
The User Delight Index (UDI) is a single number that represents your degree of satisfaction with your scope. Why delight? Because customers who are merely satisfied may not buy the product again, but delighted customers will.1
To get a balanced view of what things affected UDI, we contacted manufacturers as well as users. Three real-life examples from users demonstrate the diversity of scope applications. A fourth example, an application-specific scope, represents the attempts of manufacturers to solve niche test requirements.
Figure 1 depicts multidimensional radar plots of 14 factors that contributed to UDI for each of the four examples we focused on. More important factors within any one application are plotted a greater distance from the center.
The reason you won’t find a UDI rating on scope datasheets is simple. Your application, skill level, and experience are different than mine, so you and I may give the same scope very different UDI ratings. And because the importance each of us places upon the constituent parts of the index also varies greatly, an averaged rating is no help at all.
The UDI is a multidimensional, nonlinear, subjective, time-varying function for which there is no general solution. Nevertheless, developing and selling new products with higher UDIs are the foremost concerns of all test and measurement companies.
Is There a Scope in Your PC or a PC in Your Scope?
When scope/PC convergence was talked about 15 years ago, many people thought that the physical similarities between the two products should somehow lead to lower-cost scopes based on the PC platform. It never was entirely clear how this was going to happen.
“The idea of computers and instruments merging has been our mantra since the early 1990s,” said Bill Marcotte at Gage Applied Sciences. “As the cost of computers goes lower and lower, you will end up with a computer embedded in the instrument as opposed to an instrument inside a computer.”
Certainly, companies such as National Instruments and Gage Applied Sciences are leveraging PC capabilities to offer high-UDI solutions. These and other companies in the PC instrument business have technical strengths in software development and signal conditioning and acquisition. Their products comprise proprietary plug-in boards and associated software.
When installed and run on a PC, the overall package performs most of the functions of a conventional oscilloscope. Looked at another way, these products are PC-based data acquisition instruments with a scope-like user interface. Graphical user interfaces (GUI) add a great deal of value to these products because they can present virtual front panels that mimic the traditional controls of a scope.
Mr. Marcotte said that a factor that makes PC-based scopes easy to use “is the emergence of oscilloscope software for the Windows environment. Technicians and engineers who use Windows for daily tasks such as writing reports and corresponding via e-mail now can operate instruments as well via Windows, in an environment with which they are already familiar.”
According to Ed McConnell, marketing manager for computer-based instruments at National Instruments, “For automated measurement applications such as production test, the benefits of stand-alone scopes have diminished. Computer-based oscilloscopes offer faster performance, lower system cost, easier system integration, and better enterprise-wide solutions. Because the plug-in scopes are PCI or CPCI/PXI-based, they stream data back to PC memory much faster than the traditional GPIB or RS-232 bus. This means that automated tests run 10 to 50 times faster than those using stand-alone scopes.”
A contrasting point of view came from Tim Coll, the Infinium product manager at Hewlett-Packard. “Many R&D engineers like the flexibility that a stand-alone benchtop oscilloscope offers them. Portable, benchtop scopes can easily be moved from lab to lab. And because of the familiar scope user interface and the real-time responsiveness of the controls, engineers intuitively understand how to use the scope to debug their design.”
Scopes that consist of a PC, special software, and one or more plug-in boards are best suited to production test environments. Johnnie Hancock, a program manager at Hewlett-Packard, added, “PC-based oscilloscopes make poor troubleshooting scopes for many reasons, including slow update rates and indirect user-interface controls—they have no knobs.”
However, they do have an advantage when more than four channels must be acquired, reports must be generated online, or acquired data must be shared via a network port. Web-enabling an instrument is straightforward if it already is PC-based. Sampling speeds of 100 MS/s and higher are available with 8-bit resolution. For slower applications, several manufacturers provide data acquisition boards with up to 12- or 16-bit resolution on eight or more channels.
In his keynote address at the 1998 NI Week in Austin, TX, Dr. James Truchard, president and CEO of National Instruments, said, “We want to take advantage of the 4,000× performance improvement in the PC that has occurred during the last several years: the 2,000× increase in memory size, the 50,000× increase in mass storage, and the 200× increase in bus speeds. We need to achieve a 10× performance improvement in our products and eliminate the gap between what the PC could do and what we need to do.”
PC-Based Scopes in a Test System
An application example is provided by Jon Robertson, an electrical engineer with Caron Engineering in Wells, ME. Caron developed a PC-based test system to quantify and document encoder quality on production batches of servo motors.
“The test system simultaneously acquires six channels of data at a 15-MHz or faster sampling rate, using three National Instruments PCI-5102 boards. Pre-trigger data and digital triggers distributed via the real-time system integration (RTSI) bus card connectors allowed the boards to be synchronized,” he said. “A major feature was the capability to dump 900,000 samples of 8-bit data six channels wide to PC RAM at the selected board scan rate. Without PC bus mastering and DMA, this would have been an impossible task.”
When used with National Instruments’ VirtualBench-Scope software, the 5102 board presents digital output as a conventional scope display. In the Caron Engineering application, the 5102 acts like a data acquisition board, but one with sufficient triggering and synchronization capabilities that three of them can be used together.
At a lower, component level, there is growing convergence between scopes and PCs. Scopes are designed using the same software languages and development tools that are used in the computer industry.
The enabling technologies developed for PCs, such as USB and IEEE 1394 FireWire I/O buses, fast memories, 32-bit microprocessors, floppy disk drives, and displays, also are found in today’s oscilloscopes. For example, LeCroy highlights the speed and processing throughput of the 192-MHz PowerPC microprocessor used in its LC584AXL DSO.
Hewlett-Packard has used an embedded PC to provide a familiar Windows 95 GUI for the Infinium series of scopes. The interface is claimed to improve ease of use, particularly for infrequently needed functions.2 But the Infinium is the exception. Overall, very few stand-alone scopes embed PCs.
Ease of Use Only Part of the Story
Oscilloscope technology has progressed to the point that, for many users, the important issues are controlling and targeting the functionality that already exists. Ease of use is closely related to the user’s skill level and personal preferences. However, a discussion about ease of use is irrelevant if the scope doesn’t have sufficient horsepower to solve the problem at hand. Ease of use is not the same thing as user delight.
A niche-specific way to cope with the conflicting requirements of increasing both functionality and user delight is to target an instrument to a very narrow application. As an example, LeCroy has built several application-specific products on top of standard scope platforms. One of them, the DDA-120 Disk Drive Analyzer, starts with a 2-GS/s, 1-GHz, four-channel DSO and adds a non-return to zero (NRZ) data interface with trigger modes and waveform graphing/analysis functions designed for disk-drive testing.
So, is it a scope? Well, yes, but you wouldn’t buy it for that reason. The functions that are regularly used for disk-drive testing are relatively few in number, and their operation can be learned easily. You are provided with the correct input signal conditioning and signal processing that produces results in terms common to the disk-drive industry.
You would buy the DDA-120 because it’s a disk-drive tester with the features required to do that job. In a niche application area such as disk-drive testing, providing a structured, complete solution adds a lot to user delight.
Anticipating the generic requirements of mixed-signal testing and development is another way to achieve a high UDI rating. Mark Sullivan, a senior engineer with Niobrara Research and Development in Joplin, MO described an application on which he had spent a couple of fruitless weeks troubleshooting a transient problem.
“I was debugging an industrial communications bridge with an Ethernet interface to a 68000 processor. A transient problem with the DMA lead to a crash in an unrelated part of the code, and I just couldn’t find it. I remembered seeing a demo of the HP54645A Mixed-Signal Oscilloscope (MSO) and realized that, with the MSO, I could trigger on the cessation of ROM cycles when the CPU went crazy. Using the deep memory, I could look back in time to see what had gone wrong,” he said.
“The problem turned out to be contention of a tri-state control line,” Mr. Sullivan continued. “Because of the MSO’s synchronized analog and digital, logic analyzer-style channels, I was able to view the problem clearly and fix it within a few hours.” When compared with the specialized capabilities of the LeCroy DDA-120, few of the features used were unusual, but their integration in one instrument increased the UDI in this example.
A third way to delight users is to develop a better way to present information. The use of a Windows GUI in HP’s Infinium is an example. Today, Windows is almost intuitive, so it works well in this application.
Tektronix has developed the digital phosphor oscilloscope (DPO) which acquires and displays waveforms in yet a new way. Repetitive signals are digitized and stored in a 3-D memory array that is mapped directly to the display. Up to 200,000 waveforms are acquired per second. In addition, the intensity of pulse edges is made to vary inversely with slew rate.
The combination of a fast waveform update rate and a gray-scale intensity capability closely resembles an analog scope display. Mike Phipps, business development manager with Tektronix’s U.S. Marketing group, explained the analog real-time (ART)/DSO/DPO relationship. “The new DPO lets the engineer see, store, and analyze dynamic complex signals. In the past, the ART oscilloscope permitted the engineer to see the signal, but he couldn’t store or analyze it. The DSO added the capability to store and analyze, but signal display became the limitation. DPO fills the gap.”
LeCroy’s analog persistence mode produces displays that look like those of the DPO, but LeCroy emphasizes long memory compression rather than very high-speed waveform update rates. Gould’s TruTrace® feature also compresses long-memory acquisitions and helps you see activity variations within an overview of a single-shot event.
It is interesting to note that oscilloscope manufacturers have taken more than 15 years from the introduction of the DSO to rediscover the importance of the Z axis. The technologies developed by Tektronix, LeCroy, and Gould have gone part way toward regaining the benefits of an analog scope display. As higher resolution LCDs become more readily available, and manufacturers gain experience from their first-generation DPO-like products, waveform display will continue to improve.
New Features in Scopes
For a long time, “higher, wider, deeper, faster, cheaper” has been the standard phrase describing scope progress. But now it is changing. As shown in Figure 2, customers at the peak of the triangular graph of oscilloscope price vs volume remain insatiable in their demands for more features, speed, and memory. Note that the 1999 market has a more narrow peak and broader middle region than the 1990 market did.
This view of the scope world accounts for the gradual downward migration into mainstream products of what started as high-end features. As mainstream scopes become more powerful and less expensive, new technology provides even higher performance for those relatively few users who absolutely must have it.
With so much affordable performance available, new features often appear in important, but more specialized, functional areas. Triggering, speed of display update, display appearance, sampling resolution, and differential inputs are some of the areas that manufacturers are addressing. Of course, lower cost can improve sales volume, provided that functionality hasn’t been reduced as well.
Dr. Michael Lauterbach, director of product management at LeCroy, commented that, “As signals become faster, the capability to trigger on glitches, runts, or edge transition times down to 600 ps becomes important. Another feature is exclusion triggering that causes the scope to trigger only on anomolies. If a signal’s transition- time specification is 1.0 ns ±20%, the scope can be set to trigger only on edges faster than 0.8 ns or slower than 1.2 ns.”
Each of the new features that a scope manufacturer develops has been well researched. What is hard to determine, however, is how various sets of features are used together.
For example, Jerry McCord, a test engineer with Products Unlimited of Sterling, IL, described the application that prompted the purchase of his latest scope, a Fluke PM3394. “We manufacture contactors, relays, and transformers. In our test lab, we must monitor several events simultaneously, such as AC from a current transformer, AC across a coil, and DC from a battery. Each channel needs to have isolation. We wanted a portable, easy-to-use scope that could be moved from teststation to teststation, with the capability to measure at least four waveforms at the same time. The scope also had to trigger well in an inductive environment without a lot of false triggers and had to operate reliably in temperatures up to 100°F.
“We use internal delay triggering, four-channel operation, glitch capture, signal filtering, and cursor measurement options,” Mr. McCord said. “Sometimes, the roll mode and the capability to print results are very useful.”
Because many of the tests he performs require viewing multiple AC cycles, he uses fairly slow time-base settings. “I find glitch capture reassuring—I know I haven’t missed something at low speeds,” he said.
The PM3394’s inputs are single-ended and not isolated from ground or from each other, so Mr. McCord transformer-couples voltage signals and uses a clamp-on ammeter for current monitoring.
In-rush current measurements and verification of relay operating speed are two of the faster tests he deals with. For these, he has made sure that the scope’s sampling speed is great enough to capture the detail he requires at the appropriate time base.
Cursor measurements are basic amplitude and time, but Mr. McCord does appreciate the improved accuracy a built-in measurement system gives him compared with estimating values by eye. Finally, he said that, although he has used analog scopes for many years, and that the dual analog/digital operation of the Fluke scope was an initial reason to buy it, he has never switched out of the digital mode.
These four examples emphasize the difficulty of defining and evaluating the UDI. A high UDI rating may depend upon detailed characteristics—subheadings—within any of the main categories shown in Figure 1. Other factors, such as the manufacturer’s application support or his repair and warranty policies, can delight or frustrate a user and that, too, may affect his scope’s UDI.
At a higher level, the oscilloscope market has segmented into a rich mix of bench, hand-held, rack-mount, PC-based, and special-purpose test instruments. Within each of these major sections, manufacturers provide several platforms from which a multiplicity of products are offered.
For example, improved display, integrated circuit, and battery technologies have enabled smaller, lighter, portable scopes, but field applications have driven the market for them. Communications and power are two areas where rapid growth and new specifications have created a large demand for on-site test tools.
Hybrid instruments also have a place. Brad Byrum, general manager of the Yokogawa test and measurement division, explained: “Our Model DL708E ScopeCorder has the triggering, man-machine interface, and zoom capabilities of a DSO; the triggering and high channel count of a logic analyzer; and the high-resolution, signal-conditioned front-end measuring capabilities of an oscillographic recorder. It can simultaneously measure thermocouples, digital logic inputs, and 10-bit analog waveforms.”
Divergence from a one-size-fits-all mentality clearly is the approach the scope industry has taken to improve customers’ UDI ratings. Proliferation of a wide variety of scopes and scope-like products will be supported in the future by new technologies such as system on a chip (SoC), very-high-speed microprocessors and memories, and computer bus standards.
1. Peters, T., Liberation Management, Alfred A. Knopf, New York, 1992, pp. 701-715.
2. Beane, M., “Memory Specification Is an Important Oscilloscope Performance Indicator,” EE-Evaluation Engineering, July 1998, pp. 18-26.
NOTE: This article can be accessed on EE’s TestSite at www.evaluationengineering.com. Select EE Archives and use the key word search.
Analog Oscilloscope Family
Features Auto Setup
The CS-5300 Series of two-channel analog oscilloscopes is available with either a 50-MHz or 100-MHz bandwidth and with or without cursors and readouts. Accuracy is ±2% for both horizontal and vertical axes. Dedicated rotary knobs and push buttons are used for control, and LEDs indicate the status of major functions. Standard features include TV frame and line triggering and a delayed B sweep mode. Models CS-5370 and CS-5350 also provide auto setup of vertical and horizontal axes and automatic voltage and frequency measurements. From $1,485 to $2,035. Print Products International, (800) 638-2020.
Large, Bright CRT
The Model 6510 two-channel, 100-MHz bandwidth, four-trace analog oscilloscope incorporates a 6″ × 6″, 12-kV CRT with internal graticule. The specifications include ±3% accuracy, 5-mV/div to 5-V/div sensitivity, ×5 magnification, and 400 VDC plus AC maximum input voltage. The input impedance for channels and the external trigger is 1 MW . A 20-MHz bandwidth limit switch and Z-axis input are additional features. Two ×1, ×10 probes; an AC power cord; and an operating manual are provided. $975. HC Protek, (201) 767-7242.
Analog and Digital Modes
Require No Compromises
A 100-MHz bandwidth analog scope and a 40-MS/s digital scope are combined in the two-channel Model 5105. Glitch detection of events >50 ns long reduces errors caused by under-sampling at slow time-base speeds. Input sensitivity ranges from 1 mV/div to 20 V/div in 14 calibrated steps. Roll, refresh, and envelope display modes; interpolation; and both IEEE 488 and RS-232 interfaces are included. Up to four 8-kpoint traces can be stored, and there are 17 automatic measurement functions. A single button switches between analog and digital functions. $2,695. B+K Precision, (714) 237-9220.
Scope Display Tracks
A continuously variable time base in the Model PM3394B 200-MHz bandwidth analog/digital oscilloscope can be synchronized to rotating machines or engines. The sampling rate is 200 MS/s for transients and 25 GS/s for repetitive signals. Included are state, pattern, video, and glitch triggering; vertical and horizontal magnification; and a mode that retains 8-bit resolution in each of four vertically stacked trace windows. The built-in DSP provides rapid FFT calculation, digital filtering, integration, and differentiation. Trace memory is 8-kwords per channel. From $7,245. Fluke, (800) 443-5853.
Control Software Provides
Multiple Windows, Time Bases
GageScope is Windows-based software for controlling the CompuScope family of data acquisition cards with sampling speeds up to 500 MS/s. The software allows you to set vertical scaling, capture mode, pre- and post-trigger depth, and other triggering, input, and display parameters. Up to 32 channels, waveform cursors, multiple windows with different time bases, and the capability to save and load traces are supported. An optional Waveform Parameters plug-in provides rise/fall time, pulse width, and frequency measurements. An optional plug-in computes up to 1,000,000-point FFTs. GageScope: $495; waveform plug-in: $250; FFT plug-in: $250. Gage Applied Sciences, (800) 567-4243.
Digital Display Mimics Analog
The TDS3000 family of two- and four-channel color digital phosphor oscilloscopes (DPOs) comprises six models with 10-kword memories. Bandwidth and sample-rate combinations are 100 MHz, 1.25 GS/s; 300 MHz, 2.5 GS/s; and 500 MHz, 5 GS/s. The 7-lb, portable instrument displays up to 5,000 500-point acquisitions per second for examination of complex, dynamic waveforms. A rechargeable battery provides up to two hours of operation when not connected to the AC supply. Optional plug-in modules are available for FFT, advanced triggering, and extended video triggering. A Centronics interface is standard. GPIB and RS-232 interfaces are optional. TDS3000: from $2,995; modules: $495; GPIB or RS-232: $395. Tektronix, (800) 426-2200, code 1116.
High Speeds, Long Memories
Handle Complex Signals
The LC584AXL DSO features a 1-GHz bandwidth, four-channel, a 2-GS/s sample rate, and 4-Mwords of memory per channel. Hardware can be stacked to give up to 8 GS/s and 16 Mwords on a single channel. An Auto Scroll mode with a selectable zoom expansion and scrolling speed can automatically play back the acquired signal. Other features include a 10″ color VGA display; analog persistence; and pattern, slew rate, runt, state, video, and exclusion triggering modes. An optional timing and jitter analysis package measures and displays signal statistics. $39,990. LeCroy, (914)578-6020.
Combined Scope and Recorder
Has Multiple Input Channels
The Model DL708E ScopeCorder accepts up to eight inputs. Signal conditioning modules for voltage (10 bits @ 10 MS/s or 16 bits @ 100 kS/s), temperature, or strain are available. A history memory allows you to review up to 1,000 previous screen captures. Standard features include a 10.4″ TFT display; up to 4 Mwords/channel memory; a real-time, built-in printer; a floppy disk drive; and Centronics, GPIB, and RS-232 interfaces. A 2.1-GB internal hard disk with real-time recording in the roll mode, a SCSI interface, and user-defined math operations are options. Starts at $5,370. Yokogawa, (800) 258-2552.
Instrument Combines DSO,
Data Acquisition, Recorder
The DataSYS 7200 Fast Recording Scope is a 200-MHz bandwidth, four-channel, 8-bit resolution, color DSO. A high-resolution mode of operation acquires 12-bit data continuously, recording it to an integral 500-MB hard drive. The instrument also includes a chart recorder mode in which full bandwidth data is written continuously to an integral thermal plotter at speeds up to 50 mm/s. Playback with expansion, compression, and search also are features. From $9,950. Gould, (216) 328-7000.
Emphasizes Ease of Use
The Infinium Series of five DSOs provides a Windows 95 environment for use with complex measurement functions. The front-panel layout closely resembles an analog scope. Windows 95 has the depth to address more complicated functions without requiring specialized training. Specifications range from the Model 54810A two-channel, 500-MHz bandwidth, 1-GS/s sampling rate DSO with 32-kwords of memory to the 54845A four-channel DSO with a 50-W input bandwidth of 1.5 GHz and a 4-GS/s sampling rate. From $9,995. Hewlett-Packard, (800) 452-4844 ext 5257.
Scope Inputs Accept Signals
From Real-Life Applications
The Integra family of four-channel transient and recording digital storage oscilloscopes features color displays, floppy disk drives, direct to writer recording, parameter measurements, and long memories. The Integra 10 is an entry-level, 12-bit resolution model with a monochrome display and a floppy disk drive and differential inputs as options. The 12-bit resolution Integra 20 includes a dual sample-rate acquisition system, GPIB I/O, 500-kHz bandwidth differential inputs, and optional integrated signal conditioning. The 8-bit resolution, 200 MHz bandwidth Integra 60 addresses high-speed transient capture. Integra 10: $7,190; Integra 20: $11,990; Integra 60: $7,990, Nicolet, (608) 276-5600.
PC-Based Scope Offers
The Model PCI-5102 is a two-channel digital storage oscilloscope board with a 20-MS/s rate and 8-bit resolution. It plugs into a host PC having a PCI bus. Standard VirtualBench-Scope software does not require programming to provide a soft front panel. Features include a separate external trigger input, an adjustable trigger level, repetitive sampling up to an equivalent 1-GS/s rate, simultaneous input channel sampling, and a 15 MHz bandwidth. A Real Time System Integration (RTSI) bus has one clock line and seven trigger signals to synchronize multiple devices. A Windows NT/95/3.1-compatible instrument driver is available. With two ×1/×10 probes: $1,295. National Instruments, (512) 794-0100.
Copyright 1999 Nelson Publishing Inc.