Page 1161 - The Mechatronics Handbook

45

Measurement

Techniques: Sensors

and Transducers

45.1 Introduction
45.2 Motion and Force Transducers
Displacement (Position) Transducers • Velocity
Transducers • Acceleration Transducers • Force
Transducers
45.3 Process Transducers
Fluid Pressure Transducers • Fluid Flow Transducers
(Flowmeters) • Liquid Level Transducers • Temperature
Transducers
Cecil Harrison 45.4 Transducer Performance
University of Southern Mississippi 45.5 Loading and Transducer Compliance

45.1 Introduction

An automatic control system is said to be error actuated because the forward path components (comparator,
controller, actuator, and plant or process) respond to the error signal (Fig. 45.1). The error signal is developed
by comparing the measured value of the controlled output to some reference input, and so the accuracy
and precision of the controlled output are largely dependent on the accuracy and precision with which
the controlled output is measured. It follows then that measurement of the controlled output, accomplished
by a system component called the transducer, is arguably the single most important function in an
automatic control system.
A transducer senses the magnitude or intensity of the controlled output and produces a proportional
signal in an energy form suitable for transmission along the feedback path to the comparator. [The term
proportional is used loosely here because the output of the transducer may not always be directly
proportional to the controlled output; that is, the transducer may not be a linear component. In linear
systems, if the output of the transducer (the measurement) is not linear, it is linearized by the signal
conditioner.] The element of the transducer which senses the controlled output is called the sensor; the
remaining elements of a transducer serve to convert the sensor output to the energy form required by
the feedback path. Possible configurations of the feedback path include:
• Mechanical linkage
• Fluid power (pneumatic or hydraulic)
• Electrical, including optical coupling, RF propagation, magnetic coupling, or acoustic propagation

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