How to program labview to read data channel by channel?

[Xiaotong0428]

Hello,

    I was trying to measure 36 differential voltage channels with USB 6255 and found the noise to be high. I think the problem is due to the crosstalk when scanning between channels. Is there a way to program the labview so that I can read all data from channel 0 and then go to other channels? Thanks.

[GerdW]

Hi Xiao,

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@Xiaotong0428 wrote:

I was trying to measure 36 differential voltage channels with USB 6255 and found the noise to be high. I think the problem is due to the crosstalk when scanning between channels.

Is there a way to program the labview so that I can read all data from channel 0 and then go to other channels?

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So when you read only one channel then there is no (substantial) noise?

Anyway: surely you can read from one channel only. All you need to do is to configure your DAQmx task correctly…

What exactly do you mean when you write "read ALL data"?

[crossrulz]

Here are some ideas for eliminating ghosting: How Do I Eliminate Ghosting from My Measurements? 

My preferred solution is the third item given: use a Voltage Follower op-amp configuration to lower the source impedance for all of your channels.  This allows the muxed ADC capacitor to properly charge/discharge before taking a reading.

[Xiaotong0428]

Hello, thanks for your reply. I want to try the example 2 second case (figure 1, read all 100 points from channel 0 and then channel 1) to decrease the noise from the software side by avoiding settling time between channels. My current labview program is like figure 2. The daqmx read configuration is Analog->Multiple channels->Multiple samples->1D wavefrom(Samples). So I think the program is doing as the case 1 of example 2(read one point of channel 0 and then channel 1 until finishing 100 points of all channels).

[Xiaotong0428]

Hello, thanks for the advice. I think changing the hardware might be a little difficult for me so I want to try software change first like decreasing the sample rate, just to reduce the influence of settling time between channels. If that doesn't work I will add voltage folloer to decrease the impedance.