PLC Programming Fundamentals – ONS One Shot Instruction

The ONS, also known as the One Shot, instruction will allow the rung to execute once if the data leading to it is true. The instruction will not let the rung to evaluate again until the input is set back to LOW and then HIGH. The One Shot instruction is extremely useful when you need to execute a certain instruction once. A common example would be saving initial parameters of a process when it’s initialized. The ONS is found on the input side of a ladder logic rung structure.

This is a companion discussion topic for the original entry at