Intro to Control Systems

There are two types of control systems, open loop and close loop. A control system regulates the behavior of a system using control loops. There is a process variable, which is what is being controlled, and a setpoint which is the desired value of the process variable. In open loop systems, the value of the process variable is ignored when determining control actions. An example of this is a drying machine. Let us assume the drying machine has a moisture sensor, and the amount of moisture would be the process variable. We want the dryer to dry the clothes completely, so the setpoint would be 0. The control action would be turning the machine on and off. In an open loop system, we would ignore the process variable, and just set a timer for how long run the dryer(we would try and calculate it beforehand so the setpoint would be met), so the control action would be independent of the process variable. In a closed loop system, the control action of turning the dryer off would not occur until the process variable reaches the setpoint(completely dry). To do this, the dryer would constantly need to update and check the state of the process variable, thus creating a feedback loop getting feedback from the moisture sensor until the setpoint is reached.