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LCD storage scopes are low cost performers

Posted: 02 Nov 2004 ?? ?Print Version ?Bookmark and Share

Keywords:model 6810cn? model 6810mn? protek test and measurement? oscilloscope? rf spectrum analyzer?

Protek Test and Measurement is one of those smaller test-and-measurement vendors that you don't hear too much about. Nonetheless, the company has been successfully offering a line of relatively low-cost test gear for more than 10 years now.

In addition to oscilloscopes, Protek has RF spectrum analyzers, signal generators, sweep generators, and frequency counters in its product line-up, as well as instruments such as LCR meters, DMMs, clamp-on ammeters, sound-level meters, and even digital-display lab-type power supplies.

Low cost, but powerful

With its latest imported wares, Protek joins a number of vendors offering inexpensive digital storage oscilloscope capabilities. While many competing scopes rely heavily on a host PC for number crunching and display purposes, Protek's LCD-equipped scopes can work standalone, or in conjunction with a computer.

These sampling scopes should appeal to you if you're involved with equipping an engineering school lab, or a production-line application where they may be subject to some abuse.

When you consider their price tags, their menu-driven interfaces, soft keys, and high-res displays (features you'd expect on much more costly boxes), Protek's instruments shape up as remarkable bargains. Support, maintenance, and repair may be another matter, but I'll leave those cost-of-ownership matters up to you to resolve with Protek.

Mono or color

Kudos to Protek for offering two versions of its dual-channel digital scopes. If you want to go all out, you can choose the Model 6810CN, with its 5.7-inch VGA LCD. It's priced at about $1,300, including a pair of probes.

If you're on a budget, though, and don't mind looking at signals on a monochrome screen, the Model 6810MN should fill the bill, and save you a few dollars (about $135) in the process. While that difference may seem trivial to some scope buyers, in this price range it's a meaningful percentage of overall instrument cost.

USB connectivity

In step with the times, both of these oscilloscopes include plug-and-play USB connectivity. With that, you can operate almost all front-panel controls from a Windows PC. USB also lets you offload waveform data into PC files.

And, as the company's press statement notes, you can also optionally add modules to implement RS-232 serial I/O (operable from 300bps up to 38.4kbps) or even IEEE-488.2/GPIB interfaces. The RS-232 module costs about $320. The talker/listener GPIB option will set you back about $450.

Again, having these communications options can cost-effectively tailor one of these low cost boxes to your application, depending on what you need. The options make the 6810CN and 6810MN scopes applicable for manual bench-level use, in automated test suites, and in PC-hosted environments.

Speaking of options, Protek's datasheets indicate that a flash array is an option, but Protek applications engineer Roy Taffaro says that the company isn't supplying the flash card option. Taffaro says Protek is supporting a special Pass/Fail module, however. The Pass/Fail option can come in handy if one of these scopes is to be used by a semi-skilled operator, or in production-line settings.

Conventional look-and-feel

In use, both instruments impart the look and feel of conventional bench scopes, with no surprises. However, you can also run Protek's optional Ultra-Scope software to get more functions. It comes on a CD-ROM, runs on any Windows PC, and costs $146.

From the front panel, you can set the sweep rate from 50s/div out to a fast 2ns/div, in the conventional 1-2-5 sequence. What's more, a zoom feature takes the sweep down to 10ps, if need be. Accuracy is rated to be within 100ppm, with a resolution of 40ps in non-zoom modes. The 100ppm accuracy is attributable to the use of a TCXO (temperature-compensated crystal oscillator) timebase. Stable TCXO references are nifty features in instruments in this price range.

In use, you can acquire 4,000 samples/channel, using a number of internal and external triggers. The high-Z 8-bit input channels accommodate analog signals in ranges extending from 2mV/div up to 5V/div, with choice of AC or DC coupling. Accuracy of these inputs is rated at 3 percent.

Not mentioned in Protek's release notes is the fact that these instruments offer a variety of automatic measurement modes and math operations. Auto measurements include peak-to-peak amplitude, RMS, and max/min measurements. You can also automatically measure average and overshoot levels, frequency and period, pulse widths, rise times and fall times, delay times, and duty cycles, to name a few.

Math operations include adding or subtracting both channels, and multiplying them. As the press release notes, you can also make spectral measurements using the system's FFT (fast Fourier transform) functions.

The FFT mathematically computes frequency from stored time-domain information. In use, you can do a 1024-point FFT with choice of Hanning, Hamming, Blackman-Harris, or rectangular weighting. The use of four FFT windows gives you tradeoffs between amplitude accuracy and frequency resolution.

- Alex Mendelsohn


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