Instrument Control (GPIB, Serial, VISA, IVI)

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GPIB bus insulation fiber optics

What is the cheapest solution to avoid ground loops, electrical perturbation,... between
my computer and sensitive instruments controlled by GPIB?
I can probably use two GPIB140A fiber optic extender, but I DONT need a long optical fiber
between the computer and instruments. Is there some compact GPIB controller, which electrically isolate the bus lines?
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We do offer a controller that connects to the PC through ethernet (P/N 778209-01).

Note that on some the desktop boards, such as the at-gpib/tnt there is a jumper labeled W1, This jumper is used to short the signal ground line (pin24) and shield line (pin12). These two pins are shorted in order to help reduce noise. Most gpib devices short these two lines internally. These desktop boards also short these lines by default. Therefore, if a jumpered board or one of these devices mentioned above exist somewhere on the GPIB bus, the two lines will be shorted throughout the entire system. The user has the option to disable this short in the case of a potential ground loop.

To fix ground problems on the PCI-gpib you can remove resistor R12. This will take it out
of CE spec, so make a note of it. Removing this resistor is the equivalent of removing jumper W1 on the boards listed above.

PCMCIA cards, on the other hand, do not short these lines internally. Furthermore, the PCMCIA GPIB cables are inherently noisier. If these two ground lines are not shorted anywhere on the bus, there may be communication problems. Data may not be transmitted correctly. The ibwrt function, for example, may return a timeout (EABO) because data is not getting across the bus.

The way to resolve this problem, if it occurs, is to pop the top off of the PCMCIA card and shunt the resistor R5. Or, just connect another device onto the bus. Since most of the time laptops are run off of a battery, there is no worry about ground loops so shunting the resistor should work fine.

You can order these products at ni.com/catalog.
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