Tall and shallow or short and deep?

In January and February, LeCroy and Tektronix introduced oscilloscopes that feature large displays and shallow footprints (Ref. 1). Design engineers like this tall form factor because the instruments use little bench space. But what about test-system builders? Taller scopes consume scarce rack space while leaving the space behind them potentially unused. To find out what oscilloscope form factors work best in test systems, I spoke with several test-system integrators.

Jay Nemeth-Johannes, CTO of CompleteTest, was more open to tall scopes. "The Tektronix DPO7000 is 17.75 in. wide, so it should fit nicely into a rack. If the system needs another tall instrument," he noted, "it may fit nicely side by side with the new large-screen scope. Instruments that don't fit in the traditional 19-in. rack are nothing new." He expressed some concern about vertical space consumed by the tall form factor. "If a physical display is important, then get a scope that's easy to use. If not, then use a modular scope and a virtual display."

The traditional short and deep oscilloscope form factor saves rack space over tall scopes designed for the bench. Courtesy of Instrumentation Engineering.

Brooks isn't alone in his sentiment. "PXI digitizers and scopes are available from several suppliers," added N.D. "Buck" Smith, principal at Cal-Bay Systems. "They typically have 14-bit or 16-bit resolution and sample at up to 200 Msamples/s. Other PXI scope cards with 8-bit resolution sample much faster."

While modular scopes offer an alternative to box scopes, IE's Schlenker likes boxes because he can operate a scope offline to troubleshoot the system. "The best solution is to eliminate the display but provide a VGA output," he said. His colleague, senior software engineer Asish Shah, offered an alternative. He'd like to see a no-display scope that contains an Ethernet port and a Web server so he can operate the scope with a browser.

As I see it, the biggest problem with using a tall scope in a system isn't the form factor but the computer interface. IEEE 488 is still the I/O bus of choice for test-system builders because of its large installed base. An IEEE 488 port is standard on the DPO7000, optional on the LeCroy WaveRunner Xi, and not available on the DPO4000. I expect IEEE 488 ports to slowly disappear as designers switch to USB or Ethernet.