I was trying to locate some information on capacitive sensors so naturally, I turned to the World Wide Web to see what I could find. As I was looking through the search engine results, I found a link to Sensors Magazine, and a two-part article on capacitive sensors that I highly recommend you read. Capacitive Sensor Operation Part 1: The Basics and Capacitive Sensor Operation Part 2: System Optimization do an excellent job in describing the basics through what you need to consider in applying capacitive sensors.
In addition, I found a terrific online resource called Engineer on a Disk. This web site has a forum, electronic books (check out the ebook: Automating Manufacturing Systems with PLC’s), notes and special materials. What brought me to this site was an excellent overview of sensors called Presence Sensing.
Check out these links! They are very informative and a great resource. Let me know what you think or if you have any other resource recommendations.