Chapter 6 Electromechan e r m m c a a ni cal a S Sy s st ems e s 153 Copyright Goodheart-Willcox Co., Inc. Copyright Goodheart-Willcox Co., Inc. Activity 6 -6 Solenoids Objectives A solenoid is an electromagnetic coil with a movable core constructed of a magnetic material. The core or plunger is sometimes attached to an external spring. This spring causes the plunger to remain in a fixed position until moved fi by the electromagnetic fi eld created by current applied to the coil. This external fi spring also causes the core or plunger to return to its original position when the coil is de-energized. Solenoids are used for a variety of applications. For example, most door chime circuits use one or more solenoids to cause the chime to sound. Many gas and fuel oil furnaces use solenoid valves to turn the fuel supply on or off automati- cally on demand. Most dishwashers use one or more solenoids to control the flow fl of water. The solenoid is representative of the many types of electromechanical control devices used in conjunction with robotic systems. In this activity, you will learn the basic operation of the solenoid by observing a solenoid as it is used to operate door chimes. Equipment and Materials • Digital multimeter. • Door chimes (low voltage, 6–24V). • Variable dc power supply. • Air-core coil (200 turns, No. 24 wire) or equivalent. • Cold-rolled steel core, 3/4″ diameter, 6″ ″ long or suitable substitute. ″ • SPST switch. • Connecting wires. Procedure 1. Adjust the multimeter to measure resistance. Measure and record the resistance of the air-core coil to be used in this activity. 2. Connect the circuit as shown in the following. + 40 V Air-core coil SPST Goodheart-Willcox Publisher Solenoid test circuit.