Special Control Circuits

Question 1

Name the three basic types of timing devices:

Answer 1

Spring-wound interval timers
Mechanical and electronic time switches
Timing Relays

Question 2

State an application of a Mechanical Timer:

Answer 2

Security Lighting
Landscape irrigation
Controlled Parking receptacle circuits

Question 3

Spring-wound interval timers and time switches are reliable, inexpensive and commonly used. T or F?

Answer 3

True

Question 4

What sort of a timing device can have their operation controlled Pnematically (air pressure) or by a fluid-filled dashpot?

Answer 4

Timing Relay

Question 5

Electronic Timing Relays are smaller, more accurate, versatile and more cost-effective than pnematic or dashpot relays. T or F?

Answer 5

True

Question 6

Delay on release is another name for what basic timed-contact function?

Answer 6

Time Delay on De-Energization (TDOD)

Question 7

TDOE can allow time delays of 0.05 seconds to 300 hours. T or F?

Answer 7

True

Question 8

What timing functions can have their relay contacts change position immediately?

Answer 8

TDOD
Interval Timing
Repeat Cycle Timing

Question 9

Name the other timing functions apart from TDOE and TDOD:

Answer 9

Interval Timing
One-shot Timing
Repeat Cycle Timing

Question 10

Multi-function timing relays may offer a reset terminal as a well as a _______ terminal.

Answer 10

Start.

Allows for a remote manual reset of the timing sequence or, if connected to an automatic pilot device, feedback is provided to the relay for automatic-process-condition control.

Question 11

Why is a timing relay used in a Wye/Delta starter?

Answer 11

To allow the motor to come up to speed before it automatically changes over to Delta.

Question 12

Describe Mechanical Friction Braking:

Answer 12

Connect a friction brake mechanism onto the motor shaft. The solenoid coil of the brake release is connected in parallel with the motor power leads and becomes energized when motor is energized.

Question 13

To apply dynamic braking, a braking resistor is placed across the armature. T or F?

Answer 13

True

Question 14

A motor can be stopped faster if it is connected in such a way that it acts as a generator. This is called:

Answer 14

Dynamic braking or magnetic braking

Question 15

The amount of braking can be controlled by changing the value of the braking resistor, which in turn changes armature current. This type of braking is for:

Answer 15

Dynamic Braking for DC Motors

Question 16

Dynamic Braking of AC Motors is called:

Answer 16

DC injection braking; dc current is applied to the stator winding of the motor

Question 17

An application that requires immediate stopping would need what method of braking?

Answer 17

Plugging : reverses the supply to two of the windings

Question 18

Anti-plugging generates a large amount of heat in the rotor due to the kinetic energy of the rotor and the coupled load. T or F?

Answer 18

False. This describes Plugging

Question 19

An Anti-Plugging switch is controlled by the rotation of the motor shaft. T or F?

Answer 19

True

Question 20

What sort of application would require an Anti-plugging braking method?

Answer 20

An application that requires the motor or load to coast to a stop before it can be reversed.

Question 21

A control circuit carries the electric signals responsible for directing the performance of a control device. T or F?

Answer 21

True

Question 22

Transformers dont have internal impedances. T or F?

Answer 22

False

Question 23

Indoor transformers have to be enclosed style. T or F?

Answer 23

False. Indoor transformers can be enclosed style or open style.

Question 24

If the higher voltage of 480 is required on the primary side of a 240/480V Transformer, the windings are connected in parallel. T or F?

Answer 24

False. To acquire 480 on primary it should be connected in series, if you wanted a 240 value, it would be connected in parallel.

Question 25

What type of fuse is recommended to protect a control transformer?

Answer 25

Time Delay