Question 1

Why do most solid-state DC motor controls use some method to limit the current to a safe value?

Accepted Answer

If the controller is turned on with full voltage applied to the armature, or if the motor stalls while full voltage is applied to the armature, a very large current will flow. This current can damage the armature of the motor or the electronic components of the controller.

Question 2

The armature of a large DC motor has high resistance.

Accepted Answer

The armature of a large DC motor has low resistance in order to have a large current flow through the coils and produce a powerful magnetic field.

Question 3

How is a DC motor operated below normal?

Accepted Answer

The motor can be operated at below normal speed by applying rated voltage to the field and reduced voltage to the armature.

Question 4

An electrotachometer is connected to the ____________________.

Accepted Answer

The answer of An electrotachometer is connected to the ____________________....

Question 5

In a field failure control, what happens if the voltage falls below a certain level?

Accepted Answer

The answer of In a field failure control, what happens...

Question 6

How is normal speed for a DC motor obtained?

Accepted Answer

The answer of How is normal speed for a DC...

Question 7

A very common method of detecting motor speed is with the use of a(n) ____________________.

Accepted Answer

The answer of A very common method of detecting motor...

Question 8

If load is added to a motor, the motor speed increases.

Accepted Answer

If load is added to a motor, the motor speed decreases because more torque is required to overcome the additional load.

Question 9

The shunt field power supply is generally designed to remain turned on even when the main (armature) power supply is turned off.

Accepted Answer

The shunt field power supply is independent of the main (armature) power supply and is designed to remain turned on even when the armature power supply is turned off. This is to ensure that the shunt field continues to create the necessary magnetic field for the motor to operate when the motor is turned on again.

Question 10

The greatest advantage of using direct current motors is their variable ____________________ characteristic.

Accepted Answer

The answer of The greatest advantage of using direct current...

Question 11

A DC motor is generally operated at or below normal speed.

Accepted Answer

A DC motor is designed to operate efficiently at or below its rated speed, as exceeding this speed can lead to excessive wear, reduced control, and potential damage to the motor.

Question 12

Output voltage control is achieved by ____________________ the SCRs.

Accepted Answer

The answer of Output voltage control is achieved by ____________________...

Question 13

If current flow through the shunt field is interrupted, a compound wound, DC motor will become a series motor and race to high speeds.

Accepted Answer

When the shunt field current is interrupted, the field weakening effect disappears and the motor operates as a series motor, which has a higher speed-torque characteristic. This can cause the motor to race to high speeds and potentially damage the motor or connected equipment.

Question 14

Speed control of a DC motor is much smoother if two separate ____________________, which convert the AC voltage to DC voltage, are used to control the motor instead of resistors connected in series with the armature.

Accepted Answer

The answer of Speed control of a DC motor is...

Question 15

What is an electrotachometer?

Accepted Answer

The answer of What is an electrotachometer?...

Quiz 35: Solid-State Dc Motor Controls