# The differences between manipulated variables and control variables

In control theory, are manipulated variables and control variables the same concept or is there a subtle difference between them?

Manipulated variables and control variables are the same concept. They are the variables that are used to control the process, e.g. the output of the controller. I'm not sure why there are two different names for the same thing, but I guess it's because the industry and academia often develop different lingo because they have different goals.

The variable that is subject to control is called the controlled variable by some people. It shouldn't be confused with the control variable. I prefer to use the name process variable (PV) instead of controlled variable.

• I wonder why i sometimes see control and manipulated variables together such as here (In the HTML version) and many other examples. Dec 29 '17 at 12:12
• I don't even see the abstract, that's the problem. I only get the login page. Anyway, by searching I found this article. It uses the name control variable for y and manipulated variable for u, but also uses controlled variable for y. So it's poor wording in my opinion. It should've used controlled variable everywhere for y. The same goes for most of the other results I looked at. Safest bet is probably to look at the variable names: u is process input and y is output. Dec 29 '17 at 13:19
• Apology, here is the screenshot. Dec 29 '17 at 13:28
• It uses control variables where it should have used controlled variables. Dec 29 '17 at 14:01
• Language is inprecise its not just industry vs academia. Its person to person. Language barriers, different subcultures of field, historical reasons and all come to play. Dec 29 '17 at 14:16

Manipulated variable and controlled variable are not necessarily the same thing. For example, take a water tank level control system where make up water flow into the tank is the manipulated variable and tank level is the controlled variable. There are many other examples besides this one.

• Many thanks. You are talking about controlled variable. But I mean control variable not controlled. Jan 2 '18 at 2:35