Most process control and monitoring applications will have one or more of these fundamental controls:
Simple control is where a control output is simply turned on or off. A single discrete output is used to control the process and typically two discrete inputs are monitored. Although this type of control system is quick and easy to implement, the control is rather crude (hard to closely maintain a setpoint). A good example is the thermostats used on home water heaters, air conditioners, and even your car's cooling system.
With proportional control, analog inputs and outputs are used to maintain an exact setpoint. The controller is typically a PID controller.
Although level, pressure, temperature, and flow are the most common -- almost any parameter that can be measured can usually be controlled. You can control pH, salinity, oxygen concentration, percent solids, chemical composition, etc.
The process engineer (expert) will know what variables have to be controlled and how to control them. Your job as the systems integrator is to accurately measure the process variable (PV), set-up a PID controller, and tune the PID controller.
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