Noise when sampling fast from different channels from one MCC device to another

[msmith]

Hi - I have a USB-3100FS that sends out 3 analog outputs. They go to 2 places, one is a recording device that samples at 30 kHz and another is to a breakout box attached to a MCC PCIe-DAS1602/16 board via its analog inputs (which I use for real time sampling to control an experiment). What I see is the following - when I run code on the computer with the PCIe-DAS1602 board that samples slowly (let's say 10 Hz), everything is fine and I have no issues. However, when I sample rapidly (let's say 10kHz) from two or more of the outputs of the USB-3100FS, I see noise on all of the lines from which I sample (which makes it to the recording device, and I can see it in real time). So essentially, rapid sequential sampling from the USB-3100FS outputs introduces noise. This is entirely predictable from code. If I don't run the code on the PCIe-DAS1602 to do the sampling, everything is fine. As soon as I sample quickly (and it has to be going back and forth between 2 or more channels, and doing it fast) the problem is introduced.

The question is this - is there something I should do to remove this noise? My suspicion is that I need to setup better grounding between my devices, potentially making sure the USB-3100FS and the PCIe-DAS1602 are grounded together. But I'm not sure and would like some guidance.

Thanks!

[Fausto]

Hello @msmith.

The MCC USB-3101FS has a low output impedance of 0.1 Ohms and an output update rate up to 100 kS/s per channel.

The MCC PCIe-DAS1602/16 has an input impedance of 10 MOhms and an aggregate sampling input rate of 100 kS/s, since the analog inputs are multiplexed to the ADC.

What is the output rate and output range of the signals from the MCC USB-3101FS channels?

Configure the analog input channels on the MCC PCIe-DAS1602/16 board for differential mode.

What is the input range of the analog input channels on the MCC PCIe-DAS1602/16 board?  Choose a narrow range.

Regards,

Fausto

[msmith]

The output rate is about 1 kHz, and the range is +/-5V typically (though we've also tried +/- 10V). I configured the PCIe-DAS1602 for differential and that didn't seem to help. I am using comedi in Ubuntu to read from the board, and have been working to specify the input range as well.