Summary Review of Units 5-11 (DC Motor Controls)

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OBJECTIVE

  • To give the learner an opportunity to evaluate the knowledge and understanding acquired in the study of the previous seven units.

A. Complete the following statements.

1. A dc motor starter is designed to limit the ____

2. A three-terminal starting rheostat provides protection for a shunt motor.

3. Since the holding coil of a four-terminal rheostat is connected across the source, this type of rheostat provides protection to a motor.

4. A four-terminal rheostat may be used with a motor for which a wide range of ____ control is required.

5. Series motor starters provide either ___ protection or protection.

6. A drum controller is used when the operator has __ control of the motor.

B. Select the correct answer for each of the following statements and place the corresponding letter in the space provided.

7. The three-terminal starting box can be used with all but the:

a. compound motor.

b. shunt motor.

c. series motor.

8. Interpretation of automatic circuits requires the recognition of:

a. color. c. parallel circuits.

b. rating. d. electrical circuit symbols.

9. A piece of apparatus which contains a minimum of one set of contacts operated by a coil is called a:

a. motor. c. relay.

b. magnet. d. dynamo.

10. Normally closed contacts are

a. open at all times.

b. open when the relay coil is deenergized.

c. open when the relay coil is energized.

d. closed when the relay coil is energized.

11. An elementary automatic motor controller circuit diagram shows the:

a. actual wiring layout.

b. schematic motor diagram.

c. actual sequence of operations of the entire circuit.

d. sequence of operations of the starting circuit only.

12. One type of automatic controller operates on the basis that the counter emf generated in a motor

a. increases the starting current.

b. energizes a starting relay.

c. de-energizes a starting relay.

d. reduces the field current.

13. Another type of controller accelerates the motor in steps by:

a. using a series of thermal elements.

b. allowing starting resistor voltage drops to energize relays.

c. operation of relays controlled by speed.

d. cam controlled relays.

14. A controller is called a series lockout relay starter because the:

a. starting resistors are bypassed and locked out.

b. relays are all connected in series.

c. relay coils are connected in series with the armature and cause each relay to lock out (open).

d. relay coils lock themselves out of the circuit.

15. A remote-controlled motor reversal requires:

a. one relay with two contacts.

b. two single contactor relays.

c. two double contactor relays.

d. two interlocked relays.

16. The principle of dynamic braking involves a. the use of a dynamo as a brake.

b. the use of an electromagnetic brake connected across the motor armature.

c. connecting a low resistance across the motor armature.

d. connecting a brake relay across the armature.

C. Complete each of the statements at the left by selecting the letter(s) of the appropriate phrase or phrases from the list at the right.

17. Undervoltage protection is provided in

18. Dynamic braking is used for

19. Multiple-step acceleration is used for starting

20. Automatic starters provide more uniform acceleration than

21. A sealing circuit's used in

a. quick stopping.

b. large motors.

c. a three-terminal starting rheostat.

d. a four-terminal starting rheostat.

e. small motors.

f. series motors.

g. manual starters.

h. control circuits.

22. Match each of the following symbols with its description at the right.

1._Normally closed pushbutton

2._Thermal motor overload relay

3._Shunt relay coil

4._Normally open contact

5._Fuse

6._Normally closed contact

7._Normally open pushbutton

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