I'm looking for a generic term/process that explains how we can make a closed- loop control system.

The typical elements of a closed loop systems are controller, actuator, plant and sensors.

If you consider a closed loop system with negative feedback loop, it feeds the error to the controller by subtracting the out-put from the desired value.

I'm interested to know how does exactly it happen in real world example?

As far as I know the feedback loop provides an electrical signal, the value that we provide ( the desired value ) is just a string of bits and bytes, so there should be something here right before the controller to do the subtraction operation.

How dose exactly this whole process happen ?

I know engineers design/simulate the whole thing in MATLAB/Simulink or ... . But I don't know the process that turns the simulation into a real ( physical ) final product.

  • $\begingroup$ Look at the mechanism in the tank of a toilet that maintains the water level. That's a closed loop. $\endgroup$
    – Pete W
    Jul 22, 2021 at 20:42

2 Answers 2


Microprocessors. The measured value from a sensor (either an analog voltage or any other digital processed value) provides the microprocessor with the current output of the system. Internally, this has stored the desired setpoint, and computes the next control input by indeed taking the difference of the output and the setpoint using any kind of arithmetric logic unit. Do note however that (assuming the controller is implemented properly) the control signal does not computes derivatives or integrators, but uses previous inputs and outputs in a digital controller sense. This is especially important for slower microprocessors.

These come in many forms, think of industrial PLC units or FPGA's. However, mostly, they are embedded and do not work like your computer's CPU (speaking of software wise). This is because usually, you need a processor that only processes one thing: the controller. Doing so ensures the controllers sampling rate can be kept consistent, which is important to guarantee performance and stability of said controller.

  • $\begingroup$ Questioned answered. I should ask this in another question but, can you tell me if the subtraction ( arithmetic ) operations is hardcoded into the microprocessors ? Or we can program those microprocessors ? while they are in operation or overhaul ? $\endgroup$
    – user14407
    Jul 22, 2021 at 21:28
  • $\begingroup$ As far as I can tell yes, I took a quick peak at the instruction list for the ATmega328p (the microprocessor used in an Arduino), both ADD and SUB(tract) are present instructions. While I expect that one could also just ADD the negative number to achieve the same. Hereby the negative number is expressed using the Two's complement. $\endgroup$
    – Petrus1904
    Jul 23, 2021 at 9:56

I'm looking for a generic term/process that explains how we can make a closed-loop control system.

There's a pretty good definition over on Electronics Tutorials:

A Closed-loop Control System, also known as a feedback control system is a control system which uses the concept of an open loop system as its forward path but has one or more feedback loops (hence its name) or paths between its output and its input. The reference to “feedback”, simply means that some portion of the output is returned “back” to the input to form part of the systems excitation.

Closed-loop systems are designed to automatically achieve and maintain the desired output condition by comparing it with the actual condition. It does this by generating an error signal which is the difference between the output and the reference input. In other words, a “closed-loop system” is a fully automatic control system in which its control action being dependent on the output in some way.

I'm interested to know how does exactly it happen in real world example?

Here's an example which is purely mechanical. No electronics, no bits and bytes and no Matlab.

enter image description here

Figure 1. A mechanical governor. The vertical shaft is driven by the engine and the faster it goes the more the weights are thrown outward and upward (against gravity) causing the lever arm to reduce throttle. Source: Centrifugal governor.

These governors are used on steam and diesel engines such as on diesel generators which must run at constant speed to maintain mains frequency. Note that the feedback is negative. Increase in feedback causes the fuel to be reduced.

The typical elements of a closed loop systems are controller, actuator, plant and sensors.

Element Component
Plant The engine.
Controller The governor and lever.
Actuator The throttle valve.
Sensors The centrifugal weights.

Have a look at Diesel engine speed governor explained to see a US military training film for more on this.

If you can grasp the principle of operation of this it should be easy enough to translate the principles to an electronic control.


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