GPIB still rules, for now
Martin Rowe, Senior Technical Editor -- Test & Measurement World, 4/1/2003
The venerable IEEE 488 bus, commonly called GPIB, has long held the top spot as a communications bus for connecting computers to instruments. Other buses have appeared, most notably Ethernet and USB, which some people claim will make GPIB obsolete. In certain applications, these people may be right, but ask most engineers who build test racks which bus they use in new systems, and they'll tell you that GPIB is king.
To find out why GPIB still dominates, I asked several test engineers and other representatives of instrument makers. Jay Nemeth-Johannes, CEO of test-consulting firm Complete Test (www.completetest.com), says that GPIB has plenty of life left. "GPIB will be around for at least another 10 years," he explains, "because there are so many instruments in use today that rely on the bus." He likes GPIB because its connectors and cables provide a ruggedness that you can't get from Ethernet or USB. GPIB connectors and cables are shielded and contain numerous grounds, and you can't easily pull it from its socket the way Ethernet and USB connected grounds can come out.
Test engineers like to use existing equipment and code for as long as possible. Linda Rae, general manager of Keithley Instruments (www.keithley.com), says that GPIB will remain dominant in tests for at least another 10 years. "GPIB has an enormous installed base, and many instruments in use today have GPIB only. Many test engineers have no choice but to use it." Rae says that RS-232 ports will disappear first, replaced by USB or Ethernet ports. But Rae predicts that even 10 years from now, new test racks will rely on GPIB to control instruments.
Agilent Fellow Joe Mueller echoes Raes' thoughts. Mueller says that instruments will have GPIB ports on them for at least five years, perhaps as long as 10 years, though USB and Ethernet ports will appear alongside GPIB. Given that many test instruments stay in service for 10 years or more, engineers will build systems with GPIB communications for 10 years after the last GPIB-equipped instrument leaves the factory.
Despite its widespread use, test engineers seem to have a love-hate relationship with GPIB. Although they see shortcomings in the bus, many test engineers use it anyway. Bill Drago, formerly of L-3 Communications (www.l-3com.com) and now a consulting test engineer, says "I don't like GPIB. The cables are too big, instruments often hang up the bus, and communicating with instruments is too complicated. I'd drop GPIB if I found a better alternative, but I can't take the time to learn how to use another interface."
Fortunately for Drago, he may not have to. The VISA I/O driver lets you use the same instrument commands for GPIB or Ethernet connections. Now, the VISA driver also supports USB. (The May issue of Test & Measurement World will include an article that explains how to use VISA with USB). But until enough instruments come with Ethernet and USB ports, Drago will have to use GPIB.
Martin Rowe, Senior Technical Editor, m.rowe@tmworld.com
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In "Get your
hands around a DMM" (February 2003, p. 12), we stated that the
Protek Model 506 has a nonisolated serial port. The user
documentation and Protek's Web site didn't identify the isolated
port at the time the article went to press. Protek later provided us
with a schematic showing the isolated port and has since updated its
Web site. We also stated that the Model 506 lacked Windows software. The company provides a Windows-based application with each meter. 
