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GPIB-USB-B Grounding and Isolation

Hardware: GPIB>>External Controllers/Convertors>>GPIB-USB-B, Signal Conditioning Other>>6B Series

Problem:
I have a system setup where the PC that holds the GPIB-USB-B is grounded at a different potential than the GPIB instrument I am using. I have used PCI-GPIB in place of the GPIB-USB-B in the same PC for years without issues, but I had to send the GPIB-USB-B in for repair. Is there a problem with the grounding?

Solution:
Yes. The GPIB hardware does not have isolation built into it. If you have a system where there are different ground potentials involved, the voltage difference could surge through the GPIB hardware and cause damage. The same could happen for the PCI-GPIB and the PC, but the voltage difference may be at a level where the PC chassis served as an alternate path to ground, which could explain why the PCI-GPIB did not have problems.

To prevent further damage to the GPIB hardware or other components in your system, do any of the following:

  1. Buy a GPIB-120A, which can provide up to 1600 V electrical isolation between GPIB systems. These are available at ni.com.
  2. Buy a pair of GPIB-140A units, which extend a GPIB system using fiberoptics. Since the GPIB signals at each end are transformed into fiberoptic signals, each unit can reside at a different ground potential. These are also available at ni.com.
  3. For the GPIB-USB-B, use a USB isolated hub. National Instruments does not sell these, but there should be many available for sale elsewhere on the web or in local stores.
  4. Change the system setup so that all components in the system share the same earth ground to eliminate the possibilities of voltage differentials running through the system.


Related Links:
Product Catalog: GPIB-120A Expander/Isolator

Product Catalog: GPIB-140A Extenders

KnowledgeBase 2WSFACDS: GPIB-USB-B No Longer Functions After Cycling the Power or Disconnecting the Instrument

KnowledgeBase 2TU8722Y: Do the ports of the ENET or USB Serial boxes provide isolation?



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Report Date: 06/16/2004
Last Updated: 12/09/2005
Document ID: 3AFDDRYF

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