Labview setup - differential volts 6225 ?

[asquit]

HI, I've got a simple stub here which I want to make differential voltage measurements with a pci - 6225 , one SCC and one SCB module, External clock, external trigger. it runs, but the waveforms I get back are 16 single ended , not the 8 diff I want . The answer must be simple, I don't see and differential examples nor help, but point me to the FAQ if you know of one...

thanks

Alex

[Margaret F.]

Hello!

Thank you for posting to the NI Forums! Differential measurements as I'm sure you know references one terminal to another instead of to ground. So, when we set up a differential task, the first half of the channel count of a card will be referenced to the latter half making the latter half unusable for input.

The reason that you are seeing 16 channels is becuase you have chosen 16 channels in the first half of the channel count, so they are all usable. So, currently you are inputing on 16 channels that are being referenced to 16 channels in the second half of the channel count. If you want 8 channels differential, just pick 8 channels in the first half of the channel count. If you set up a differential task and then choose for instance channel 55 of  your 6225, LabVIEW will throw an error becuase that channel is not available in differential mode.

Hope this helps!

[asquit]

Alas, it seems the lack of signal on the input chans seems to be a new new hardware problem , possibly with the SCC-68 connected to channel 0. Connector 1 has an SCB-68 , and I can see a signal in differential mode with ai48 , which is on the SCB-68, right ?  No signals in ai0:8 nor ai16:23 when the same input is applied to them. Do I need to address differential channels differently when an SCC-68 is connected ? there are no expansion mods installed. 

thanks for your help

[Margaret F. · Accepted solution]

Hello,

Can we try swtiching which connector the SCC-68 and SCB-68 are connected to? This would help us determine if there is a problem with these connectors. Let me know!

[asquit]

Thanks, but I've found the problem, upstream of my stuff alas. I was getting signals, and they were just noise. all better now,talk, people ! 

sorry to trouble you

Alex