How sensors uses in real time process control

Sensors send data (through an analogue to digital converter - ADC) to a microprocessor or computer that decides whether or not to take action (based on comparison with stored data). If a change is required to be made, computer/microprocessor transmits signals (through a digital to analogue converter - DAC) to devices being controlled and alters their status (for example turn a heater on if a temperature sensor indicates that a temperature is too low) - actuators are often used to open valves, turn on equipment etc. As this is continuously monitored, eventually the temperature will equal the stored value in computer/microprocessor - this will then cause the heater to be turned off.