Voltage on unconnected pins

[romesh]

I am trying to read 10 pressure sensor inputs using USB6218 channel a0 - a9 and a labview application. To start with I just connected one input(ch a0), but on my labview application I configured my DAQ assitant for reading 10 channels, Finite samples (while loop), 10 samples to read at 100Hz. I read all the pressure samples on my channel 0 took an average and determined whether there is any leak on my cards by comparing it to a threshold. The result was as I expected on channel a0 but in addition to that I get few false positives on the unconnected inputs (read random voltage though there is nothing connected to those pins).Is it possible to detect this condition in Labvew application when it happens in manufacturing line. I would like to solve this in FMEA when no card is connected to the input channel. Please need some advice.

[RavensFan]

This isn't the correct forum for this question as this forum is for fieldpoint or compact fieldpoint devices.  You will want to post in the Multifunction DAQ board.

But what you are seeing is a phenomenon known as ghosting.  Try searching on that term.  Basically, when you try to read the unconnected channel, you are seeing remnants of your previous read because you have an infinite impedance input which prevents the A/D converter from discharging completely.

What does "FMEA" mean?  I don't understand what your application is.  What card are you talking about on what manufacturing line?

[Margaret F.]

Hello,

If I am reading your post correctly, you are seeing a voltage reading on channels that you do not have anything connected to. This is the behavior of any open analog channel. The voltage will inevitably float. You could detect this in LabVIEW by writing some code to read these "empty" channels and handle the non-relevant data however you would like.

I too am unfamiliar with FMEA. Can you elaborate?

Thank you,