Timer are used in PLC program to introduce some delays in a logic transition.
On-Delay Timer
For an On-delay timer two different types of contact.
NOTC - Normally opened,timed -closed.
This timer is normally open and that is going to take some time to close.
Contact is open when the relay coil (Timer Input for PLC programming) is de-energized.
When the relay is energized there is a time delay in closing.
NCTO - Normally-Closed,Timed -Open
This timer is normally closed and that’s going some time to open.
Contact is closed when the relay coil is de-energized
When the relay is energized,there is a time delay in opening.
Off delay Timer
NOTO (Normally Open,Timed Open) -
Contact is normally open when the relay coil is de-energized.
When the relay coil is energized,the contact closes instantly.
When the relay coil is de-energized,there is a time delay before the contact open.
NCTC - Normally Closed,Timed Closed Contacts
Contact is normally closed when the relay coil is de-energized.
When the relay coil is energized,contacts opens instantly.
When the relay coil is de-energized,there is a time delay before the contact open.
