8.1 Introduction

Noncontact sensors and measurement devices those that monitor a target without physical contact provide several advantages over contacting devices, including the ability to provide higher dynamic response to moving targets, higher measurement resolution, and the ability to measure small fragile parts. Noncontact sensors are also virtually free of hysteresis, the error that occurs with contacting devices at the point where the target changes direction. With these noncontacting sensors there is no risk of damaging a fragile part because of contact with the measurement probe, and parts can be measured in highly dynamic processes and environments as they are manufactured.

Noncontact sensors are based on various technologies including electric field, electromagnetic field, and light/laser. Two complementary sensor technologies will be discussed in detail in this chapter: capacitive electric field based, and inductive (eddy current) electromagnetic field based.

Figure 8.1.1: Noncontact sensor system.

A capacitive or inductive sensor consists of a probe, which is the actual physical device that generates the sensing field, and a driver, the electronics that drive the probe and generate the resulting output voltage proportional to the measurement. In some sensors, the driver is physically integrated in the probe itself.

Capacitive and inductive noncontact sensors have many similar characteristics as well as some characteristics unique to each technology. In the following pages we will discuss those things which are common to each of the technologies, compare those things which are different, and look at applications for each and at the unique...