Problem: Differential mode, measures 1.4 V, USB 6009

Hi everyone

I'mmeasuringcharging and dischargingtwo capacitors, individually.

I'm using the USB 6009;

Two capacitors, twographs, two analog inputs(AI0 +, AI01-) and(Al1 +, Ai1-);

I configuredin differential mode; ok

Problem:

When acapacitor isswitched off, it measures1.4V