2 - TRANSDUCERS — DISPLACEMENT, REFERENCE AND VELOCITY

Abstract

This chapter discusses displacement, reference, and velocity of transducers. The range of devices available to provide transduction of displacement—rectilinear or angular—is considerably greater than that for any other variable. Moreover, many of these displacement measuring devices form the secondary element in transducers for other variables such as temperature, force, torque, acceleration, tension, liquid flow rate, liquid level, and liquid density. Displacement transducers, which are also known as position transducers, are used primarily as feedback transducers in position control systems, which are called, alternatively, servomechanisms or servo systems. However, other versions of these may be used as reference transducers for a wide variety of control systems, especially, where the reference variable value is to be set manually. Velocity transducers, which are also known as rate transducers, are used mostly as principal feedback transducers in velocity control systems and as secondary feedback transducers in position control systems. The choice of transducer to measure velocity is very limited in comparison with the range available for displacement. This is true particularly in the case of rectilinear velocity, for which there are few devices of any significance manufactured commercially.