Analog Input baseline changes when digital output done in parallel

[dsavir]

Hi all,

We are using a USB 6008 DAQ to run a simple system. AI6 is connected to a motion sensor; digital outputs control a pump. We noticed that if we read from AI6 without performiong additional tasks, the baseline is ~0.17V and when motion is detected it goes down to 0.13V. However, if we read from AI6 while performing digital output at the same time, the baseline goes down to ~0.14V and when activated it goes down to ~0.1V, i.e. the baseline changed by 0.03V. Are we doing something wrong or is this expected behavior?

Thanks,

Danielle

[johnsold · Accepted solution]

Danielle,

You may have a ground loop. If the current from the pump or even the digital control for the pump runs through the same ground conductor as the signal from the motion sensor, the voltage drop in the common conductor due to the pump current could cause an effect like you are reporting.

Lynn

[dsavir]

Thank you! I will check.

Danielle