Simple PLC Flasher

 

This is a very simple ladder diagram that flashes the "Output". The "Output" is turned off for a period of time then turned on for a period of time and the sequence is repeated.

The "Init" contact is initially zero and by putting it normally closed it will enable the on delay timer "T1" which determines the flashing off time. When "T1" set value is counted, the contact "T1" will be turned on and the "Output" will be also turned on.

When the "Output" is on, the on delay timer "T2" which determines the flashing on time will be enabled and so "T2" contact will be on which results in turning "Init" contact on.

When "Init" is on, timer "T1" will be off because "Init" which enables it is normally closed. When "T1" is off the "Output" will be off and so timer "T2" will be off and "T2" contact will be off which results in turning "Init" contact off.

When "Init" contact is off the sequence is repeated as timer "T1" will be enabled then the "Output" after "T1" counts .. and so on.

Using only one timer:

 

Here the flasher is done using only one on delay timer, but both on and off times are the same.
Initially "Init" is off so by putting it normally closed it will enable the on delay timer "T1" and after counting to its set value "T1" will turn on "Init".
With "Init" on and the contact "Output" off the coil "Output" will be on.
In the next scan cycle "Init" is on from the first cycle so the normally closed "Init" will be off and the timer "T1" will be deactivated and the coil "Init" will be off.
From the previous scan the "Output" was on so the normally closed contact "Output" will be disconnected and the normally open contact "Output" will be on.
With "Init" off and "Output" contact on the coil "Output" will be energized.
In the next scan cycle "Init" is off so it will enable "T1" and hence "Init" coil will be energized.
With "Init" on the "Output" coil will be off and all starting conditions are returned so the sequence is repeated.

Finally I hope this program was useful for you.

Good bye.