Deck 35: Solid-State Dc Motor Controls

Question 1

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

Answer 1

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.

Answer 2

False

Question 3

How is a DC motor operated below normal?

Answer 3

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 ____________________.

Question 5

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

Question 6

How is normal speed for a DC motor obtained?

Question 7

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

Question 8

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

Question 9

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

Question 10

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

Question 11

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

Question 12

Output voltage control is achieved by ____________________ the SCRs.

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.

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.

Question 15

What is an electrotachometer?