# What is Control: Definition and 1000 Discussions

Control theory deals with the control of dynamical systems in engineered processes and machines. The objective is to develop a model or algorithm governing the application of system inputs to drive the system to a desired state, while minimizing any delay, overshoot, or steady-state error and ensuring a level of control stability; often with the aim to achieve a degree of optimality.
To do this, a controller with the requisite corrective behavior is required. This controller monitors the controlled process variable (PV), and compares it with the reference or set point (SP). The difference between actual and desired value of the process variable, called the error signal, or SP-PV error, is applied as feedback to generate a control action to bring the controlled process variable to the same value as the set point. Other aspects which are also studied are controllability and observability. This is the basis for the advanced type of automation that revolutionized manufacturing, aircraft, communications and other industries. This is feedback control, which involves taking measurements using a sensor and making calculated adjustments to keep the measured variable within a set range by means of a "final control element", such as a control valve.Extensive use is usually made of a diagrammatic style known as the block diagram. In it the transfer function, also known as the system function or network function, is a mathematical model of the relation between the input and output based on the differential equations describing the system.
Control theory dates from the 19th century, when the theoretical basis for the operation of governors was first described by James Clerk Maxwell. Control theory was further advanced by Edward Routh in 1874, Charles Sturm and in 1895, Adolf Hurwitz, who all contributed to the establishment of control stability criteria; and from 1922 onwards, the development of PID control theory by Nicolas Minorsky.
Although a major application of mathematical control theory is in control systems engineering, which deals with the design of process control systems for industry, other applications range far beyond this. As the general theory of feedback systems, control theory is useful wherever feedback occurs - thus control theory also has applications in life sciences, computer engineering, sociology and operation research.

View More On Wikipedia.org
1. ### Where is the 'Origin' on a Bode Plot?

Wasn't sure where exactly to post this. It isn't a homework problem. I am studying for my Fundamentals of Engineering exam and am struggling with control system problems. Can someone tell me where exactly the origin is on a Bode Plot? I understand the general concept of poles and zeroes but I...
2. ### Stability of LTI systems with control

Hello, I'm interessed by the following LTI system with control u : x' = Ax +Bu and x(k+1) = Ax(k) + Bu(k). In this paper (section 3): https://proceedings.neurips.cc/paper/2020/file/9cd78264cf2cd821ba651485c111a29a-Paper.pdf They seems to say that only A needs to be stable to get a...
3. ### Modelling Guy Needing Refresher

Hi everybody. I like to model dynamical systems, but over the last few years, I've been busy implementing simulations, without actually deriving their equations of motions. I'm thus here to check with members whether some systems for which I wrote the equations of motions are actually corrects.
4. ### Trouble solving for end state of two control volumes in a rigid tank

TL;DR Summary: Struggling to structure the problem and derive an analytical solution for gas expanding into other gas in a rigid tank. Preferred formulation is fixed control volumes. This is not a homework problem. The problem: Two control volumes (A and B) are in a rigid tank filled with air...
5. ### Electronics How to control a stepper motor in closed loop (PID) in arduino?

Hello, What I have I have a NEMA17 stepper motor driven by a DRV8825 driver module, an arduino uno, a multiturn potentiometer. What I want to do I want to control the stepper motors in a PID closed loop. The motor shaft will be connected to the potentiometer and I will be sure that the motor...
6. ### B Why don't neutrons bind into large out of control masses?

I'm trying to understand why neutrons don't just continually bind into large masses. As I understand it proton binding in a nucleus is governed mostly by the strong nuclear force which attracts at close distance and electromagnet force that repels. So for protons to bind, they must have enough...
7. ### B Simple yet effective way to reliably control the DC Motor speed?

As a part of our physics high-school self-study, we are making a stroboscope. We have a small 5-V DC motor that powers the strobe disk. It works as expected, but, clearly, the motor makes the disk spin at a constant speed. Is there an easy, but effective and reliable way to control its speed...
8. ### Engineering Can I use root locus when the input is the negative feedback?

I have used root locus before but my confusion now is that the input is the negative feedback. Usually when I have negative feedback I consider the the error between the input (ideal) signal and the observed signal. Also, in this case what is the tranfer function since u = -k*y, and what does...
9. ### Engineering How to implement a transfer function in Simulink with variable coefficients?

The implementations for the two filters in simulink are as follow: For the first filter: For the second one: The obtained results have values of 10^-12, while the expected results should be between 10^-3 - 10. Since it's the first time when I try t implement a tf with variable coefficients I...
10. ### I In a closed loop system with a pump, how can we control the pressure?

How can we control the pressure of the water inside a closed loop system (chiller system for example)? Let´s say, we have a pump curve and an system resistance curve that can be modified (through opening or closing some valves) In everywhere, what I see is that the intersection of the system...
11. ### B Exploring Attitude Control of Satellites & ISS

I tried a Google search on this question, and got mixed results. I was curious if satellites (and the ISS) have to burn power to stay pointed at Earth, or if any were able to use passive tidal locking instead. I did find that satellites in geosychronous orbit are less likely to use tidal...
12. ### The use of Riccati equations in optimal control theory

I know that linear control theory, in the form ##\dot{x}=Ax+Bu##, ##\dot{u}=Cx+Du##, can be put in the form of a matrix Riccati equation. But is there really an advantage to doing so?
13. ### Electric chain hoist: need help with control circuitry

I have been given an electrical chain hoist to repair. The symptom is that it suddenly stopped working. I have checked the motor's windings and they each show similar DC resistance of 0.0018 ohms. I have attached the schematic (dunno why it was rotated 90 degrees during the upload). The hoist...
14. ### This is a 3D model I made of a nuclear power plant control room

I spent the past several weeks making this 3D model of a nuclear power plant control room.
15. ### Solving the Rewinding Tension Control Puzzle: A Production Engineer's Story

So, this problem is going to require some explaining.. I'm a Production Engineer who's recently started working at an adhesive tape converter/distributor and I've been working on an industrial rewinding machine for films, tapes, foams etc. The tapes I rewind range from 0.2mm - 3mm thickness...
16. ### Where to find detailed control panel pictures of nuclear plants?

Hello, I would like to know where I can find detailed control panels pictures of nuclear plants. Not necessarily the complete control room but the main panels. I need to be able to read switches, alarms lights, etc... Have a nice day! Thanks
17. ### Understanding Feedback Control in Klystrons

I was puzzled when I thought about what happens to a klystron when it's output is fed back to it's input. This doesn't apply to magnetrons because they cannot be driven like amplifiers so they are oscillators by definition. I've dealt with audio amplifiers mostly and there almost always...
18. ### Android: API to control battery protection mode?

My new Lenovo tablet has a "battery protection mode". This is useful for example when you want to leave it on charge almost permanently, in which case the protection mode will charge and discharge between 40% and 60% in order to maximize battery life. Is there an API that can enable/disable...
19. F

### Courses How useful is control theory in computational neurosciences?

Hello, I have the opportunity of choosing an elective course on control theory before embarking for my master's program in computational neurosciences and I am weighing the pros and cons. I am looking for advice from PF members who specialized in this field. Since I have chosen enough courses...
20. ### Engineering Advanced control systems, state-space controllers

------------EDIT---------------------------------------------------------------------------- Check comment #7 for neater and faster explanation of the question statement --------------------------------------------------------------------------------------------- The symbols represent: H, water...
21. ### Control the speed of a motorcycle

As the summary indicates I want to control the speed of a petrol bike upto 60Kmph, so that it does not go beyond that. Now my questions are can it be controlled electrically, most probably I may want to control the throttle, but how to do it? What all sensors I may require one I can think of is...
22. ### Engineering How do I use Simulink to create a control system with a 2nd order ODE?

Equation: , where matrix D, C, G and F can be represented by I'm supposed to design a control system that looks like this: I am given that the dynamic model = fcn(D,C,G,dq) where the dq is the same as 𝑞̇ and d2q in the diagram is the same 𝑞̈. The default initial value of [𝑞(0), 𝑞̇(0)] is...
23. ### Looking for Pneumatic control valve information

I am looking to find out if there is a control valve type that will move a duel port cylinder in both directions but then the current to the valve is turned off the cylinder will NOT be locked up. I thought a 5/2 double coil valve would do this but it holds cylinder when current is removed...
24. ### Sliding doors operated by a remote control device

Attached are some Sliding doors images. Can they be operated with a remote control device? The remote control device will have buttons for opening & closing the left and right door. What will be the design & construction changes in the sliding doors so that they can be operated using a remote...
25. ### Engineering Statics project involving shear & moment diagram of a control arm

Part of a project I am working on (part #3…see description below) is asking us to find the internal loads (shear and moment) and draw the corresponding shear/moment diagrams of the control arm shown below. It’s a little tricky to me, because all of the members associated with these type of...
26. ### I Solving Sub-Problem for OpenAI Lunar Lander v2: Seeking Advice

I'm currently working on a pet project which is similar to the OpenAI Lunar Lander v2 (hence the problem is in a 2D context), and seeking help for a sub-problem that's been blocking me for a while. At any instant of time, I'm to find Fe: magnitude of main engine thrust, must be >0 Fs...
27. ### Previously suppressed knowledge to control the masses

I need in my story some examples of previous knowledges or technology that were once kept suppressed in order to control the masses. For example. Flour (to keep people dependent on fruits or vegetables or produce)? Electricity? concept of Pressure? What can you think of? In modern times...

29. ### What is the "observer" in PID control?

Hi, The sentence in red confused me. I've basic knowledge of control theory so, if you can, please keep it simple. I understand that with pole-placement regulator (LPR) and linear quadric regulator (LQR) one can use an observer to estimate the system's internal states rather than measuring...
30. ### How to implement PID control in Arduino w/o using loop function?

Last week I encountered a problem in my graduate project. The project was about designing an autonomous and mobile robot that picks up 9 glass tiles from a stack point and place them into a 3x3 matrix with minimum tolerance. I am using a DC motor with an infinite turn potentiometer for closed...
31. ### Engineering Control block diagram's transfer function

The ac signal is converted to DC signal which is connected to a capacitor to filter the DC signal. The filter DC signal is step down for 12volt to 5 volt using a voltage regulator. The regulated DC signal is connected to a crystal oscillator that converts the DC signal to a square wave signal...
32. ### How do you calculate the series resistance for this Triac control circuit?

Disclaimer: Some of you might easily recognize that the components and circuit I am talking about are related to one of my projects, on which I had posted some months ago. Actually, the circuit is the same as the one in my project, but the one I am posting in this thread actually uses high...
33. ### Does every control system contain an integrator?

Hi, Let's call the box in green a plant. Does every plant consist of an integrator? It has to because when \overset{\cdot }{x}(t) passes through the green box, it becomes x(t). It's an operation of integrator; integrator converts the derivative back to the variable. Could you please guide me?
34. ### 3D model I made of the Fukushima Daiichi control room

I spent the past week and a half making this 3D model using a program called Blender 3D, or the Fukushima Daiichi nuclear power plant control room.
35. ### Conservation of mass: control volume approach question

Summary:: Control volume question that has a brine solution entering a tank and mass accumulates over time. Hello, I'm currently struggling with a control volume approach question that has a brine solution entering a tank. I get to a point where I have a first order differential equation. I...
36. ### Engineering Solving Car Suspension Modeling: Understanding Input Forces and Movement Types

Hello, I'm trying to solve this problem but I'm confused with some things, is correct that in the system there are two input forces, the torque and u(t)? I assumed that the system has two free levels, which are the z displacement and theta (rotational movement), so the system has a linear...
37. ### Shaft Friction Control: Simple Solutions

Hello Everyone, I'm working on a future mechanical structure with a rotating shaft. In this project, I should be able to control the resistance on the shaft but instead of adding some extra weights on the shaft to increase inertia, I don't have any ideas. Does anyone have an idea of simple...
38. ### Steering Effort on Sailboat w/ Hydraulic Rudder Control

Greetings to everyone, Recently I bought sailboat with rudder which is actuated by hydraulic oil by cylnder and pump at steering wheel. I have been trying to calculate steering effort(feedback) on my hydraulic operated sailboat if I change my current cylnder,but nusucessfully. Problem is that...
39. ### Control Theory: Derivation of Controllable Canonical Form

Hi, I was recently being taught a control theory course and was going through a 'derivation' of the controllable canonical form. I have a question about a certain step in the process. Question: Why does the coefficient ## b_0 ## in front of the ## u(t) ## mean that the output ## y(t) = b_0 y_1...
40. ### Active burn control by using microwaves to control the detonation of the engine

I was thinking the other day, would it be possible to have microwaves heat the air fuel mixture to activation point and have the microwaves bounce back off the gas to be picked up by a computer that generates a 3d image. this 3d image could be used to heat the gas up in a uniform way so as to...
41. ### Comp Sci Calculations regarding slow-start strategy (TCP congestion control)

Like I said, I was taught during the TCP congestion control lecture what is the slow-start strategy, how it works & looks in a very high level, we never saw anything related to parameters and calculations, and after the test she gave the entire class a bonus of 35 points because she knew it...
42. ### Engineering Disturbance in a proportional control system

Hello, I found an old thread related to this question but it doesn't look correct to me so was looking for some guidance. I have equated Qo = (Q2+Q1*G) / (1+H*G) I did this by rearranging Qo=Q2+G(Q1-Q0*H) I then went on to the calculations and found before step disturbance: Qo=...
43. ### 5/3-way proportional directional control valve VPWP

how does a 5/3-way proportional directional control valve VPWP work ? and Information about the 5/3-way proportional directional control valve plss. :cry:
44. ### I Why does "control" mean "coherency" in Wigner's friend paradox?

There we read: "note that if Wigner did not know this phase due to the lack of control of it, he would describe the “spin + friend’s laboratory” in an incoherent mixture of the two possibilities". Why is this the case? Given that the author has propoede neither a citation nor a proof for this...
45. ### How to control volume by hovering & scrolling anywhere in Mac Menu Bar

Homework Statement:: How to control volume by hovering and scrolling anywhere in Mac Menu Bar Relevant Equations:: none Hi,   I use both Mac's and pc's. Mac's are great but here's one thing I can do in my pc's that I have not been able to find how to do in my Mac.   In my pc's (Win7, Win10)...
46. ### Pole placement design, Control Theory

Summary:: Control Theory root equation pole Hi, I ran into a simple question but somehow I can't get it right. My work this far: ## G_0(s) = G(s) \cdot K \cdot \frac{1}{T_I s} = \frac{k}{\tau s +1} \cdot \frac{2\beta \tau -1}{k} \cdot \frac{2\beta^2 \tau}{Kks} = \frac{2\beta^2\tau}{s(\tau s...
47. ### Directional actuator control circuit

Hi there. I want to power and control a linear actuator that is considered heavy duty. I am contemplating either using an an existing control driver or building the circuitry with various components. i want to use these attractive control buttons which are led light up...
48. ### Does creating fire break lines work to control forest fires?

I really don't want to get into politics, I am sick and tired of smelling and breathing the smoke from the forest fire in N Calif even I am living in the silicon valley. Trump said because Calif refuse to clear fire break lines, clear the debriefs, then once the fire started, there is no break...
49. E

### B Control volumes and Reynolds transport theorem

If we consider a system of fixed mass as well as a control volume which is free to move and deform, then Reynolds transport theorem says that for any extensive property ##B_{S}## of that system (e.g. momentum, angular momentum, energy, etc.) then\frac{dB_{S}}{dt} = \frac{d}{dt} \int_{CV} \beta...
50. ### Engineering How does feedback affect the transfer function of an integrating block?

The correct solution is different than my answer, I am not sure where I am going wrong?