The function of input in a PLC (Programmable Logic Controller) is to collect signals from field devices and send them to the PLC’s processor for decision-making. Inputs are the eyes and ears of the PLC — they tell the controller what’s happening in the machine or process. These signals come from devices like sensors, push buttons, limit switches, and temperature transmitters. The PLC reads whether these inputs are ON or OFF (in digital form) or measures variable values like temperature or pressure (in analog form).
Once the input data is received, the PLC processes it according to the program logic. For example, if a sensor detects an object, the input turns ON, and the PLC decides to activate an output like a conveyor motor. Without accurate input signals, the PLC cannot make correct decisions. In short, the main function of PLC inputs is to provide real-time information from the field so that the controller can monitor conditions and execute the right actions automatically.