TABLE OF CONTENTS This chapter deals with the basic passive components in ac circuits, and will help you become familiar with these devices and understand their application in instrumentation.
This chapter discusses the following:
Use of impedance as opposed to resistance in ac circuits
Equivalent circuit of a combination of components in ac circuits
Effective impedance to current flow of components in ac circuits
Time delays and time constants
Concept of phase angle
Resonant frequency
Concept of filters
AC Wheatstone bridge
Magnetic fields, meters, and motors
Transformers
Three basic components, resistors, capacitors, and inductors, are very important elements in electrical circuits as individual devices, or together. Resistors are used as loads, delays, and current limiting devices. Capacitors are used as dc blocking devices, in level shifting, integrating, differentiating, frequency determination, selection, and delay circuits. Inductors are used for frequency selection and ac blocking, in analog meter movements and relays, and are the basis for transformers and motors.
When a dc voltage is applied to a capacitor through a resistor, a current flows charging the capacitor (see Fig. 3.1 a). Initially, all the voltage drops across the resistor; although current is flowing into the capacitor, there is no voltage drop across the capacitor. As the capacitor charges, the voltage across the capacitor builds up on an exponential, and the voltage across the resistor starts to decline, until eventually the capacitor is fully charged and current ceases to...
