Input exhibits peaking on oscilloscope when DAQ is reading the node.

[DKLCEB]

Hi,

I am trying to read data from a node with my DAQ usb-6251. I've also connected the node to an oscilloscope. Whenever DAQ samples data from the node, the oscilloscope shows that the voltage shows peaking. I am wondering why this occurs because it seems to corrupt the correct voltage on the node.

[JÞB]

Input impedance!

Your scope most likely presents a load of 1-10MOhm (or 50 Ohms depending on your setting but I think we can assume you've got the 1-10Mohm option selected  )  The USB DAQ device is a "Student Aid" quality and has an input impedance of @ 140K Ohms.  When both devices are connected together you WILL see a change on the O'scope when the input is gated to the DAC inside the DAQ device.   Basically, you just re-discovered Hiesenberg's "Uncertainty Principle" and found out for yourself that the ACT of observation MUST change the reACTion you wish to observe.