Why does the PCS0902 have a large capacitance while testing the capacitance of the liquid in a plastic test tube?

Capacitance noise is large, and the contact value is only 4PF?


The plastic test tube is placed side by side on the test tube rack, and the test tube rack is ungrounded, resulting in abnormal measurement values.

Test tube ungrounded; The frame is ungrounded; Will lead to measurement interference noise. Therefore, it is important to ground both the rack and the bottom of the test tube during the test.