Double Sheet Detection

Capacitive sensors’ sensitivity to nonconductive materials enables them to measure thickness/density of papers, plastics, and other nonconductive materials. This aspect of capacitive sensors allows them to easily detect the difference between a single sheet of material and multiple sheets. Multiple feeds, or double sheets, can be a problem in myriad applications.

The capacitive sensor is placed above a grounded conductive surface which acts as a reference for the sensor. The sheets are then passed through the gap between the sensor and the reference surface. A single sheet will produce a small change in the sensor output; double sheets or multiple sheets will produce a greater output. The size of the capacitive probe’s sensing area and the distance between the probe and the reference surface determine the sensitivity to sheet thickness variations. The CPA100 is a common, low-cost choice for this application.

This application is used in copiers, printers, mass mailing assembly, currency counters etc.