Years of working with GPIB has taught me many things, but the most important has been that when it works, it's great, when it doesn't, it's very frustrating. 10 meters might be a problem, but I doubt it. GPIB will usually work 25-50% beyond the written specs, especially with so few instruments on the bus. Here's my suggestion:
1) Did you loop the GPIB chain by mistake? GPIB won't work this way. It will only work daisy-chained. 2) Move the instrument at addr 1 to another address. GPIB addresses 0 and 1 are usually reserved for the controllers. While setting an instrument at 1 shouldn't cause and issue if you're using a single controller at address 0, it might. I always avoid setting an instrument at address 1. 3) Take all the instruments off the bus. Then put them back on one at time, scanning the bus each time. Then do the 4 combinations of 2 instruments. Then do the combinations of 3 instruments. Finally, try all 4 again. This way you can isolate the problem to more certain situations. My guess is it's either a bad GPIB cable (but not necessarily the one attaching the last instrument) or a bad GPIB controller in the 4th instrument. Less likely, but still possible is a bad GPIB main controller. If you do all this and still have problems, respond with the results and I'll try to help more. Hope this helps. Dave.
