Hello
I'm currently running a NI-USB-6211 connected to an instrument running labview 8.5. What I want to do is measure 1 channel of current and 2 channels of voltage. All are separate physical channels. I am using an express VI to separate the 3 channels on the USB-6211 and I'm trying to plot them on separate stacked waveform charts in such a way that there respond independently (as they should being separate physical circuits). I can ALMOST get this to work. I can measure the current just fine. The problem is with the voltages. If I change the voltage on channel 2, channel 3 responds as well in an equal fashion (eg. increase 5V on channel 2, channel 3 increases by 5V); however if I change the voltage on channel 3, channel 2 responds only slightly (eg 5V increase on channl 3, ~0.05V increase on channel 3). Not the best result, but better than the reverse. Channel 1 is not affected by changes in voltage, but it does affect channles 2 and 3 (current increases, channel 2 and 3 voltages increase). I have no idea why this is happening. I've seen the same thing when I've used only 2 channels (current and voltage). When the current (channel 1) changes, the voltage (channel 2) changes, but when the voltage changes, the current does not. It has to be a problem with the program because I get the same behavior when I physically disconnect channel 3 (for example, it still responds when I change the voltage from channel 2). It seems like it should be a simple setup and a simple fix, but I can't figure it out.
I've included a snapshot of the program. I have it splitting the channels so I can selectively save some data to a file. I've tried simply connecting the express VI to a chart, and that doesn't work either (the voltages affect each other). I've also tried replacing the cluster with an array, but that hasn't worked either. I've tried simulating the data with sine waves and I can get that to work without a problem. I don't know what else I can do.
Thanks for your help.
Jeff
