Data look like coupled

[jeongho20000]

Hi,

I'm trying to collect data from 4 different channels by using USB-6259 BNC and LabView 2009. When I try to collect them through a DAQ assistant, if there is an input from one channel (say channel 0), the data from different channels are also changing. I think that somehow they are coupled each other. I connected my load cell to channel 0, and tri-ax aceelerometer was connected to channel 1-3.

Any ideas or suggestions?

Thanks,

Jeong 

[Norbert_B · Accepted solution]

Jeong,

the issue you describe can have two possible reasons i can think of:

a) Too high sampling frequency. The multiplexer and ADC does not settle within the sample time so you get some kind of crosstalk. This is rather unlikely since the DAQmx driver would create an error if you set the sampling frequency too high.

b) The signal sources have a high impedance. This will create crosstalk because the voltage on one channel cannot be removed by the second channel and therefore influencing the measurement. If this is the reason (i ponder it is), you will have to decouple the signal source and the measurement device by using something like optocoupler....

hope this helps,

Norbert

[jeongho20000]

Hi, Norbert.

could you tell me more about optocoupler? I'm not familiar with it. Is it a sort of built-in VI in LabView?

Thanks,

Jay

[Ben]

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jeongho20000 wrote:

Hi, Norbert.

could you tell me more about optocoupler? I'm not familiar with it. Is it a sort of built-in VI in LabView?

Thanks,

Jay

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No it is a hardware device. Search for "opto-issolators".

Or a simple 741 Op amp configured as a buffer will do the trick.

Ben

[Norbert_B]

Jay,

adding some other possible workaround:

You can insert a "shorted channel" in the scanning between channels you want to measure with. This would help too if the reason for the crosstalk are indeed high outputimpedances of your signal sources.

Norbert