A ladder logic program, which can be used as a warning signal when moving equipment, such as a conveyor motor, is about to be started.

Warning Signal Ladder Logic

The internal output INT_OTE is energized when the START pushbutton SP0 is momentarily actuated.

As a result contact B3/0 across SP0 closes to seal in the output coil INT_OTE.

Also, contact B3/0 on the second rung closes to energize timer coil, and contact B3/0 on the third rung closes to sound the horn.

After a 10 second delay period, the NC timer contact (4:0.DN) opens to automatically switch the horn off.

Pressing the REST Pushbutton SP1 will reset to the initial condition.

Test and Run

Press the start pushbutton SP0, the input address is forced, causing the output for that rung to be true and they will appear in reverse video.

Control contact across pushbutton SP0 closes, sealing in the internal output INT_OTE.

On the third rung, since the condition is true, the output at O: 3/0 is turned on and appears in reverse video.

On the second rung, since the condition is true, the timer is energized.

After 10 seconds timer is enabled opening the timer contact (T4: 0.DN) in the third rung.

This will de-energize the output coil and turn off the horn. The timer-accumulated value is reset to zero.

Author: Dr. Hadi Saadat

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