Deck 23: Solid State Control of DC Motors

Question 1

A very common method of detecting motor ____ is with the use of an electro-tachometer, a small permanent-magnetic generator connected to the motor shaft.

A)speed
B)temperature
C)use
D)rotation

Answer 1

A

Question 2

DC motors are generally operated at or above normal speed.

Answer 2

False

Question 3

Another method of controlling the voltage to the shunt field is ____, accomplished by connecting a power transistor in series with the shunt field.

A)silicon-controlled modulation
B)pulse length modulation
C)silicon modulation
D)pulse width modulation

Answer 3

D

Question 4

Shunt field power supplies intended for motors that operate above normal speed must be capable of delivering less than rated voltage.

Question 5

The ____ of a field loss relay (FLR) is connected in series with the shunt field.

A)armature
B)coil
C)phase shift control
D)diode

Question 6

A shunt field power supply converts direct current into alternating current with a rectifier.

Question 7

When a phase-shift control unit senses a voltage decrease, it increases the voltage supplied to the armature until the electro-tachometer is again producing the present output voltage.

Question 8

Normal speed for a DC motor is obtained by operating the motor at ____ rated voltage applied to both the armature and shunt field.

A)one-fourth of
B)one-half of
C)full
D)twice the

Question 9

Silicon-controlled rectifiers (SCRs) control voltage by turning on at different times during the waveform.

Question 10

One method of sensing current is to insert current transformers in the three-phase power lines supplying power to the solid-state controller.

Question 11

Some motors intended for ____ operation contain two separate shunt fields; one field is connected to a variable voltage power supply, and the other is connected to a constant voltage power supply.

A)overspeed
B)normal
C)intermittent
D)underspeed

Question 12

The amount of voltage drop across the sense resistor is ____ the current flow through the resistor.

A)less than
B)greater than
C)proportional to
D)one-half

Question 13

Feedback control occurs when an electro-tachometer feeds a signal back to the phase-shift unit.

Question 14

Power to an armature is generally supplied by a four-phase, full-wave bridge rectifier.

Question 15

The armature of a large DC motor has a very low resistance, typically less than ____.

A)one ohm
B)two ohms
C)three ohms
D)four ohms

Question 16

DC motors used in industry are never controlled by solid-state controllers.

Question 17

Shunt field power supplies are never left energized when the motor is not in operation.

Question 18

A(n) ____ commutating diode is connected in parallel with an armature to help reduce electrical noise produced in the armature.

A)reversed
B)biased
C)reverse-biased
D)inverse

Question 19

One method of controlling the voltage to a shunt field is to replace ____ of the diodes in the rectifier with silicon-controlled rectifiers (SCRs).

A)one
B)two
C)three
D)four

Question 20

Most solid-state controllers for DC motors have the ability to maintain a constant motor speed when load is ____ the motor.

A)added to
B)removed from
C)proportional to
D)added to or removed from