time delay relays (TDRs)

No matter what the application is, when a definite-purpose

solution is required, time delay relays (TDRs) can provide

simple, reliable, and economical control. Adjusting the delay

time is often as simple as turning a knob. Providing time-

delayed switching to start a motor, control a load, or affect a

process,

time delay relays (TDRs)

TDRs are typically used in industrial applications

Additionally, they play an important role for targeted logic

needs, such as in a small panel or in sub-panels. They have

a variety of features and operating characteristics, such as

compactness, economy, simplicity, and ease-of-use

time delay relays (TDRs)

On-delay timers

With an on-delay timer, timing begins when voltage is

applied. When the time has expired, the contacts close — and

remain closed until voltage is removed from the coil. If

voltage is removed before time-out, the time delay resets

Time-delay relay contacts

Time-delay relay contacts must be specified not only as

either normally-open or normally-closed, but whether the

delay operates in the direction of closing or in the direction

of opening.

Normally-open, timed-closed

Normally-open, timed-closed. Abbreviated “NOTC”, these

relays open immediately upon coil de-energization and close

only if the coil is continuously energized for the time duration

period. Also called normally-open, on-delay relays.

Normally-closed, timed-open

Normally-closed, timed-open. Abbreviated “NCTO”, these

relays close immediately upon coil de-energization and open

only if the coil is continuously energized for the time

duration period. Also called normally-closed, on-delay relays.

Off-delay timers

When using an off-delay timer, nothing happens when voltage

is applied. Closing the control input causes the contacts to

transfer Opening the control input causes timing to begin,

and the contacts remain closed. On time-out, the contacts

transfer. Closing the control input prior to time-out causes

timing to reset.

Normally-open, timed-open

Normally-open, timed-open. Abbreviated “NOTO”, these

relays close immediately upon coil energization and open

after the coil has been de-energized for the time duration

period. Also called normally-open, off delay relays.

Normally-closed, timed-closed

Normally-closed, timed-closed. Abbreviated “NCTC”, these

relays open immediately upon coil energization and close after

the coil has been de-energized for the time duration period.

Also called normally-closed, off delay relays.

Off-delay timers

Removing voltage prior to time-out resets the timing and

opens the contacts. In addition, true off-delay timers provide

this functionality (keeping contacts closed) after input

voltage is lost.

practice

question

Time-delay relays are important circuit elements in many

applications. Determine what each of the lamps will do in the

following circuit when pushbutton A is pressed for 10 seconds

and then released:

question