2-1
CHAPTER 2
SERVOS
LEARNING OBJECTIVES
Upon completion of this chapter you will be able to:
1. Define the term "servo system" and the terms associated with servo systems, including open-loop
and closed-loop control systems.
2. Identify from schematics and block diagrams the various servo circuits; give short explanations of
the components and their characteristics; and of each circuit and its characteristics.
3. Trace the flow of data through the components of typical servo systems from input(s) to
outputs(s) (cause to effect).
SERVOS
Servo mechanisms, also called SERVO SYSTEMS or SERVOS for short, have countless
applications in the operation of electrical and electronic equipment. In working with radar and antennas,
directors, computing devices, ship's communications, aircraft control, and many other equipments, it is
often necessary to operate a mechanical load that is remote from its source of control. To obtain smooth,
continuous, and accurate operation, these loads are normally best controlled by synchros. As you already
know, the big problem here is that synchros are not powerful enough to do any great amount of work.
This is where servos come into use.
A servo system uses a weak control signal to move large loads to a desired position with great
accuracy. The key words in this definition are move and great accuracy. Servos may be found in such
varied applications as moving the rudder and elevators of a model airplane in radio-controlled flight, to
controlling the diving planes and rudders of nuclear submarines.
Servos are powerful. They can move heavy loads and be remotely controlled with great precision by
synchro devices.
They take many forms. Servo systems are either electromechanical, electrohydraulic, hydraulic, or
pneumatic.
Whatever the form, a relatively weak signal that represents a desired movement of the load is
generated, controlled, amplified, and fed to a servo motor that does the work of moving the heavy load.
Q-1. What is a servo?
CATEGORIES OF CONTROL SYSTEMS
A control system is a group of components that are linked together to perform a specific purpose.
Generally, a control system has a large power gain between input and output. The components used in the
