12 Electromechanics
12.1 Basic Principles of Electromechanical Energy Conversion
12.2 emf Produced by Windings
12.3 Rotating Magnetic Fields
12.4 Forces and Torques in Magnetic-Field Systems
12.5 Basic Aspects of Electromechanical Energy Converters
12.6 Learning Objectives
12.7 Practical Application: A Case Study—Sensors or Transducers
Problems
12.1 BASIC PRINCIPLES OF ELECTROMECHANICAL ENERGY CONVERSION
Energy available in many forms is often converted to and from electrical form because electric
energy can be transmitted and controlled simply, reliably, and efficiently. Among the energy-
conversion devices, electromechanical energy converters are the most important. Electromechan-
ical energy conversion involves the interchange of energy between an electric system and a
mechanical system, while using magnetic field as a means of conversion.
Devices that convert control signals from one form to another are known astransducers, most
of which have an output signal in the form of electric energy. For example, a potentiometer is used
to convert a mechanical position to an electric voltage, a tachometer generator converts a velocity
into a voltage (dc or ac), and a pressure transducer indicates a pressure drop (or rise) in terms
of a corresponding drop (or rise) in electric potential. Thus, a transducer translates the command
signal appropriately into an electrical form usable by the system, and forms an important part
of control systems. Electromechanical transducers form a link between electric and mechanical
systems.
When the energy is converted from electrical to mechanical form, the device is displaying
motor action.Agenerator actioninvolves converting mechanical energy into electric energy. The
electromechanical energy-conversion process can be expressed as
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