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GPIB: The death that never occurred

-April 03, 2014

In the May 1994 issue of Test & Measurement World, I stuck my neck out and wrote Look over your shoulder, GPIB where I predicted that the venerable instrument bus would be overtaken by Ethernet and the Parallel Port. Then in April 2003, I wrote GPIB still rules, for now to see if things had changed.

National Instrument USB-to-GPIB converter Then in 2006, I was Wondering about instrument buses when someone commented "There is no logical reason to throw away GPIB. We have too much legacy and investment to just toss it. But going forward, LAN and especially LXI address applications that GPIB, and in some case USB, could never adequately address."

Things did change since my first article. The Parallel Port vanished, replaced by USB and yet, GPIB has defied the odds and kept going. I'm getting mixed signals now, but GPIB still has plenty of life left. For example, Keithley Instruments recently released two power supplies aimed at automated test. The company went so far as to mention GPIB in the headline of its February 18 press release: "Keithley Adds Two GPIB-Programmable Power Supplies to Series 2200 Line."

In contrast, Agilent recently released arbitrary waveform generators that don't have GPIB as a standard feature. Ethernet and USB are standard.

Is GPIB king of the instrument buses? To find out, I spoke with Agilent, Ametek Programmable Power, and National Instruments. As a general rule, GPIB is still widely used for automated test systems that need a variety of instruments. "GPIB is still entrenched," said Katie Collette, Product Marketing Engineer – Instrument Control at National Instruments. She explained that NI often hears that GPIB is still the choice because "it just works."

Despite the fact that Agilent chose to leave GPIB off of some new instruments, Market Segment Manager Doru Popescu concurs that GPIB is still a popular choice among test engineers, saying:

It {GPIB] remains the most common available interface when assembling a test system. It is robust, predictable, and typically fast enough for most applications. There is also a comfort level with using GPIB, coupled with some perceived questions generated by the newer LAN/LXI such as flimsy cables/connectors, treading on IT territory, dynamic addresses, latency, and so on. Availability of multiple interfaces on newer instruments along with various adaptors have also taken the urgency away from migrating. Surprisingly, given the choice of connecting an instrument capable of LXI, USB and GPIB, more than half the users worldwide still choose GPIB for systems.

GPIB is still popular among test engineers in the aerospace and military industries because their products have long life cycles; 20 years is not uncommon. Test equipment manufacturers are trending toward making GPIB an option to minimize the cost of the basic instrument.

When asked "Which types of instruments tend to still use GPIB?", Bill Ruff, Divisional VP, Marketing and Business Development at Ametek Programmable Power replied "We are still seeing GPIB options being specified across our DC and AC product families. I believe that in general, instruments required to provide more time-deterministic measurements may be opting for GPIB. The LAN alternative may be an instrument with 1588 capability."

From Ruff's response, it appears as though LAN with IEE 1588 can match the deterministic performance of GPIB, which uses hardware handshaking. But, your instrument must have IEEE 1588 capability. Ruff provided a graph showing the percentage of Amektek's SG series of DC power supplies that use GPIB, LAN, and neither bus.

In 2013, 15% of SG Series of DC power supplies shipped with GPIB, equal to that of LAN ports. Source: Ametek Programmable Power

Although GPIB is still high on the list of instrument buses for ATE, it's losing ground to USB in bench troubleshooting. For one thing, you don’t need a converter. The same often goes for Ethernet. It's easy, it works, and every computer has it. That's often fine for engineering applications, but in a production setting, many engineers opt for GPIB because of the robust cables and connectors, no latency issues, and no IT issues.

Many instrument drivers will work with any hardware. In automated test applications that use the VISA (Virtual Instrument Software Architecture) software layer, you need only tell VISA which bus to use. The higher-layer instrument drivers simply pass instructions to VISA, which handles the rest.

Which cabled instrument interface do you use for bench or production test?

Also see
What's up with USB in test systems?"
Keep those legacy GPIB cards or upgrade?
Using LAN in Test Systems: Setting Up System I/O
The ATE industry's hybrid theory
How do you connect your oscilloscope?
Build a USB-based GPIB controller
Using USB in the Test and Measurement Environment

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