Instek PSS-2005 Issues with GPIB

[sjmoo]

I am trying to interface with an Instek PSS-2005 power supply through GPIB-USB-HS. At first I was having difficulty even finding the device, but that was resolved after I discovered that Instek's LabView drivers were not properly written for this particular model. Now I can consistently make contact with the device through both MAX and LabView, but it doesn't behave consistently. For example, I will send a voltage of 7.14V to the PS (with current maxed at 4.9A) and it will immediately go to the set point, but it won't stay there. It will fluctuate between 7.00V and 7.14V with a favoritism towards 7.00V. This behavior occurs at all voltages and in fact as the set point gets higher the device starts to fluctuate between the set point and 1.00V. This occurs whether I have the PS output on or off. I should also point at that the PS itself reads an error while this is occuring, but when I query through MAX it returns no errors. 

I have attached the very simple code I have been using to troubleshoot. I have a feeling this error is still somewhere in the bad code I got from Instek, but I can't figure out what would cause this. Any thoughts would be appreciated. 

[sjmoo]

I have to ammend my post. I'm starting to think that the device might be timing out, which is why it drops the signal. 

[Albert.Geven]

Hi

I would only send new info to the machine when needed. At the moment you are communicating as fast as LabVIEW can the same value as a setpoint and the same boolean for enable output.

Maybe the machine has a hard time to control and communicate at the same time?

My advise: Check the previous value to the actual one and only send when there is a difference.

[sjmoo]

Thank you Albert. That is an excellent point and I hadn't even considered it.