Chapter 5 - Displacement Measurement

Abstract

This chapter discusses the various sensing methods used for displacement measurement. Common terms are introduced followed by the two most common forms of displacement interferometry: homodyne and heterodyne. Double pass, differential and swept-frequency absolute distance interferometers are also covered. The various sources of errors associated with displacement interferometry are presented, including thermal, cosine, deadpath and periodic error. Other forms of displacement sensors are then discussed, along with their error sources, including strain sensors, capacitive sensors, eddy current and inductive sensors, optical encoders and optical fibre sensors. Lastly, the calibration of displacement sensors is discussed using both optical and X-ray interferometry.