Search FAQs on the left to see if your question has been answered. Click on the dropdown to view all of the documents associated with the product. If you can't find your question, click on Ask a Question

AD7150: Capacitive effects as conductive and non-conductive materials approach the sensor

If a finger, metal or water or other conducting materials approach the
sensor, the capacitance values are decreasing. If a non-coductive plastic item 
approaches the sensor, first the capacitance values are decreasing but at
closer distances
the values appear to be increasing. So it is difficult to distinguish if a
conducting object is
approaching or a non-conductive object is moving away from the sensor.


The same phenomenon happens with both conductive and non-conductive materials.
When a part is initially brought into the electric field, some charge is
diverted to ground and a lower capacitance is measured on the CINx pin. When it
is close enough, the part increases the effective ε and this increases the
capacitance. Conductive materials will divert more charge to ground than
non-conductive materials; therefore the drop in capacitance has a bigger effect
than the increase in ε.