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DAQmx has static readings on some channels



I'm writing a LabVIEW 2010 SP1 program for monitoring and recording and it records voltage readings from some sensors through a pair of USB6008s. I have it set to doing continuous sampling at 250 Hz for noise reasons and with a buffer size of 25 on 4 differential channels per device. The problem that I am having is that I get good readings from channels 1 and 3 on each device, but channels 0 and 2 have unchanging readings around 5.2 volts. The unchanging readings each differ from one another by small amounts. Each device has a single task in the program. Test panels in MAX show that each channel is acquiring correctly in the same conditions. Spy reports show that the problem extends to the buffer. I have switched through four different USB-6008s to no effect. Resets of the computer have no effect.


What could make a data acquisition device report this way?

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Open channels sometimes tends to pick up garbage values. It might sound a silly question, but are all the channels you recording are connected? basically are the channels that are giving you garbage values are by any chance open? other thing you can try is shuffling the inputs to respective channels to rule out if it a channel issue or board issue.

Kudos are (always) welcome for the good post. 🙂
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Please let me know if you are still dealing with this issue, as well as any relevant details you can reply with.  In regards to the first reply, this could also be the issue.  Essentially if you are monitoring an open channel it's basically tied to an infinite resistance and it just going to clip off around the peak input of the Programmable Gain Amp selected range of the device 


Ben N.
Applications Engineering
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