A programmable logic controller (PLC) instruction for a normally open input device is a command that tells the PLC to monitor the status of a specific input point that is normally open.

In industrial automation, normally open input devices are sensors or switches that are in their open state when they are not actuated or triggered. When the PLC instruction is executed, it checks the status of the normally open input device to determine if it has been activated or not.

If the input device is closed, meaning it has been actuated, the PLC will respond accordingly based on the logic programmed into it.

This could include turning on a motor, activating a valve, or triggering an alarm. The normally open input device is wired to the PLC input module, which converts the physical signal from the device into a digital signal that the PLC can interpret.

The PLC instruction for the normally open input device is typically written using ladder logic, a graphical programming language that represents the logic of the control system in a series of rungs. By using PLC instructions for normally open input devices, industrial processes can be automated and controlled with precision and efficiency.

This helps to improve productivity, reduce errors, and enhance safety in manufacturing and other industrial environments.