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PXIe 6366 Analog Input Drift
Aryce
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06-01-2018 01:17 AM
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Hey everyone.
I have a PXIe 1078-chassis with a PXIe 8820 EC, and using a PXIe 6366 DAQ card with a BNC-2110 connector block.
I am taking readings from Analog Input ports 0 and 1, and they work fine, But when I disconnect the BNC cable from those ports, the readings start drifting up until it saturates at the highest value.
In my case, I have a flow controller reading acquired at port 0, and the range is from 0 to 100. When the flow is off, I get a noisy signal centered around 0.02 (an acceptable error) but when I disconnect the BNC cable, the value being read starts climbing in an exponential fashion all the way to 102.73, where it saturates, and the signal in the graph is a straight line - no noise at all.
Any suggestions? Thanks.
_Bryan
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06-06-2018 10:38 AM
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Why do you disconnect the BNC cables from the ports?
I am going to guess that you have the channel switches (below the BNC connections) in the GS position. When you remove a cable try putting the switch in the FS position. When in the GS position the equipment is looking for a grounded signal. With no cable connected the readings will just float to whatever it wants to. The FS position will reference the signal to ground and keep the signal at zero.
http://www.ni.com/pdf/manuals/372121f.pdf
Take a look at page 5.
06-07-2018 04:18 AM
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Because I I don't need those equipment for other experiments. Some need 3 connections, some need only one. What I meant is that if I were reading the free analog input ports, this happens. And my code is generic for all these experiments, and hence it reads the unconnected ports as well.
All my signals are take in FS mode; none of the switches are in GS.
_Bryan
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06-07-2018 09:04 AM
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OK, you have a few options then.
There are BNC grounding caps that you can put on the channels that are disconnected. The cap will ground the + side of the signal and keep it from drifting.
You could also modify your program to show the plot visibility checkboxes then you can hide the channels you do not want to see on your chart. A good exercise would be to ask the user how many channels they want to use when the program starts, then have the program only use the number of channels selected. That will also help clean up any data files you might be saving by only recording the channels you are using.
But it is hard to say what program changes to make without seeing your program.
