I'm using a GPIB-USB-B interface to control my test rack. The computer is a laptop running XP. When running my application code, I intermittently get an error 28. This is 'EPWR", and the error message says that the GPIB-USB-B has lost power. From the NI 488.2 documentation, "EPWR results when an interface loses power. This often results when the system goes to and returns from a standby state". Standby and suspend are turned off on the laptop, it never powers down. I'm at a loss to figure out the source of my error. Since my application takes several hours to run, this effectively prevents me from running my code. Here are some experiments I've tried so far: - Connect the GPIB-USB-B directly to the PC, or connect it through a powered hub (rated at 500 mA per port). Results: No difference, error still occurs. - Disable all the ACPI functionality that I can in the laptop. Results: No difference. - In the PC's control panel, under System/Hardware/Device Manager, 'USB root hub', when opened, has a 'Power Management' tab. On this tab, there is a checkbox for 'Allow the computer to turn off this device to save power'. I have turned this off. Result: No difference. - Monitor USB +5V with a digital oscilloscope, and see if the +5V supply ever goes away. Result: The power supply is stable, and doesn't trigger off any transients when the error occurs. - Disconnect all GPIB instruments except one, in case there is some problem with cabling or bus loading. I have tried this several times, using different instruments. Result: No difference. - Try a different PC. I have tried this some, and have not seen the error, but I don't have enough test time to be certain. At any rate, monitoring the +5V USB supply with the scope seems to remove any possibility that USB power is really being interrupted, which suggests that the true problem is not what the error message indicates. If anyone has any ideas, or has seen other problems masquerade as error 28, I would be greatly interested in hearing about it. Thanks, Terry N. trnoe@yahoo.com

Instrument Control (GPIB, Serial, VISA, IVI)

Intermittent error 28 with GPIB-USB-B

Hi,

Same problem here. I've got 4 identical test stands and intermittently I get error 28 on all of them. I've tried the hub solution to no avail. This is happening on a GPIB-USB-HS adapter though.

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Instrument Control (GPIB, Serial, VISA, IVI)

Intermittent error 28 with GPIB-USB-B

Re: Intermittent error 28 with GPIB-USB-B