In a traffic light control system, the PLC works as a central controller that senses the inputs from the traffic lights and other sensors, and then outputs signals to control the lights. The PLC is programmed to follow a specific logic, which is designed to optimize traffic flow and safety. 

PLCs are used in machine tools to control the movement of the machine's axes, the spindle, and other auxiliary devices. The PLC receives input from sensors on the machine tool, such as limit switches, encoders, and pressure sensors. The PLC then uses this input to determine the next action to take, such as starting the spindle, moving an axis, or turning on a coolant pump. 

The purpose of a temperature control system is to maintain a device at a constant temperature. Two types of actuators are commonly used to precisel y control the temperature of optics, lasers, biological samples, or other temperature sensitive devices. One is a thermoelectric, or Peltier device.