GPIB-USB-HS and usb isolator

[_zeyol_]

Hi all !

I'm trying to control an aglient scope with a labview program.

everything works fine, but for my application the scope needs to be at a different ground than the computer.

so I bought a usb isolator : http://www.bb-europe.com/product_family.asp?FamilyId=651

but when I plug the scope through it, it isn't recognised anymore by windows. If I plug the GPIB-USB-HS alone it isn't recognized neither.

The GPIB standard speed is 1.8Mbits/s so I choose the UH401SL (Low speed), and the GPIB-USB-HS is compatible with USB 1.x so for me it's not a problem of transfert speed...

any ideas ?

thx

[SAMUEL_NIF]

Hello,
Did you try this KB ?
http://ae.natinst.com/public.nsf/web/searchinternal/12619aaeda596b5f862576cd00742c44?OpenDocument
Regards

[_zeyol_]

thanks, but the link doesn't work for me...

I solved the problem a few time ago : it wasn't a speed issue, but a power issue. indeed, the GPIB-USB-HS needs to be powered by the computer, so it requires 500mA, but the USB isolator is powered by the USB port too, and can provide only 100mA to its down port.

so with an high speed isolator equiped with an external power the problem was fixed 🙂

[JasonSmith · Accepted solution]

Power would have been a problem, but speed probably was as well. The GPIB-USB-HS is designed for USB 2.0 High Speed, but also works with USB 1.1 Full Speed(12 Mbits/s). It was not designed to work with USB Low Speed, because most computers with USB implemented USB 1.1 or later. It is virtually impossible to find a USB port that doesn't support at least Full-Speed, but apparently this isolator is an exception. Low-Speed is generally reserved for devices with bandwidth needs approaching zero, such as keyboards.

I should also point out that the maximum speed of the GPIB-USB-HS is 1.8 Mbytes/s, which is 14.4 Mbits/s, before factoring in USB protocol overhead or traffic from other USB devices on the system. This puts it slightly above the capabilities of USB Full-Speed, and far above what can be supported with USB Low-Speed.

-Jason S.