Special control Circuits Flashcards
(22 cards)
What are the three basic types of timing devices used in electrical circuits?
Spring-wound interval timers, mechanical & electronic time switches, timing relays
These devices are essential for controlling timing in various electrical applications.
What are the three methods of controlling the timing of a relay?
Pneumatic, fluid dash pot, electronic
Each method utilizes different mechanisms to achieve timing control.
What does TDOE mean?
Time delay on energization
Indicates the delay period before the relay contacts change state after energization.
What does TDOD mean?
Time delay on de-energization
Refers to the delay period before the relay contacts change state after de-energization.
When a TDOE relay is first energized, what is the contact state of NO, NC, and NC IC?
NO: open, NC: closed, NC IC: open
This is the initial state of the contacts upon energization.
When a TDOD relay is first energized, what is the contact state of NO, NC, and NC IC?
NO: closed, NC: open, NC IC: closed
This state occurs immediately after the relay is energized.
When a TDOE relay has timed out, what is the contact state of NO, NC, and NO IC?
NO: closed, NC: open, NO IC: open
Reflects the contact state after the timing period has expired.
When a TDOD relay has just de-energized, what is the contact state of NO, NC, and NO IC?
NO: open, NC: closed, NO IC: closed
This state represents the contacts immediately after de-energization.
Name three additional functions provided by a multi-function timing relay.
Interval timing, one-shot timing, repeat-cycle timing
These functions expand the versatility of timing relays in various applications.
In interval timing, once the timer has expired, what is the state of NO and NC contacts?
NO: open, NC: closed
This describes the change in contact states after the interval timing is complete.
How is the timing period initiated in one-shot timing?
A signal at the start terminal
This signal triggers the timing sequence for one-shot operation.
What is repeat-cycle timing?
A repeating timed change between contact states until the relay is de-energized
This function allows for continuous cycling of contacts based on a set timing interval.
Why is a timing relay used in a wye/delta starter?
To allow the motor to come up to speed before switching to delta
This is crucial for reducing electrical stress on the motor during startup.
What device would be used to turn on a sprinkler system at the same time every day?
Mechanical timer
Mechanical timers are commonly used for scheduling irrigation systems.
What is the correct term for contacts that begin timing when the relay is energized?
Time delay on energization
This term specifically refers to the timing function associated with energization.
Which timing function does not need continuous power to complete timing?
Time delay on de-energization
This function allows timing to complete even after power is removed.
Which timing function is used for a blinking ‘Don’t Walk’ signal?
Repeat-cycle timing
This function is ideal for creating blinking signals in traffic systems.
What happens if a braking resistor burns out in a DC motor using dynamic braking?
The motor comes to a stop due to inertia of the armature and load
This results in a loss of braking effectiveness and potential safety hazards.
What is the most likely result of plugging a motor too frequently?
The rotor bars can melt
Frequent plugging creates excessive heat and stress on the rotor.
How do you wire a 120/240 V primary and 12/24 V secondary transformer for 120 V input and 24 V output?
Primary windings in parallel, secondary windings in series
This configuration is essential for achieving the desired voltage outputs.
What is the maximum size of primary fuse permitted for a 240:120 V, 5 kVA transformer?
30 A
This fuse size is determined by the transformer’s capacity and safety standards.
