Chapter 6 Electromechan e r m m c a a ni cal a S Sy s st ems e s 157 7 Copyright Goodheart-Willcox Co., Inc. Copyright Goodheart-Willcox Co., Inc. 3. Construct the circuit shown. Be sure that the variable dc power supply is adjusted to zero. The multimeter should be adjusted to measure dc current on the highest range. 4. Slowly adjust the variable dc power supply from zero until the 6V lamp is turned on. Record the current measured by the multimeter when the relay is energized. This is the pickup current. 5. Slowly adjust the variable dc power supply toward zero until the 6V lamp is turned off. Record the current measured by the multimeter when the relay de- energized. This is the dropout current. 6. Turn the variable power supply off. 7. Alter the circuit as shown. 8. You will notice that the only difference in the two circuits is the type of contacts used. In step 3, the normally open contacts were used. In this procedure, the normally closed contacts are used, causing the lamp to remain on until the relay is energized. 9. Adjust the variable dc power supply and record the pickup and dropout currents as you did in steps 4 and 5. + + NO NC 6 V lamp 6 V battery Relay coil R1 1K mA Goodheart-Willcox Publisher Circuit using electromagnetic relay. + + 6 V lamp NO NC 6 V battery Relay coil R1 1K mA Goodheart-Willcox Publisher Circuit with relay contacts reversed.