What is Feedback: Definition and 245 Discussions

Feedback occurs when outputs of a system are routed back as inputs as part of a chain of cause-and-effect that forms a circuit or loop. The system can then be said to feed back into itself. The notion of cause-and-effect has to be handled carefully when applied to feedback systems:

Simple causal reasoning about a feedback system is difficult because the first system influences the second and second system influences the first, leading to a circular argument. This makes reasoning based upon cause and effect tricky, and it is necessary to analyze the system as a whole.

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  1. E

    Engineering Unable to model Transresistance amplifier with feedback correctly

    I spent the whole day trying to figure why transresistance amplifier modelled with z-parameters does not match with nodal analysis results but I sill can't figure out. I desperate need help on this... I write down step by step what I did for a very simple transresistance amplifier here and hope...
  2. P

    Praise My feedback, one month and half experience in PF so far

    Hello everybody I have being in PF for about one month and a half and I would like to share my advice on my experience on the site so far. I am still figuring out how it works and what is the best use of this site. Due to some setbacks I have mixed feelings but still positive on continuing...
  3. K

    What Are Trophy Points and How Do They Work?

    Sorry, but what on Earth are trophy points for? I can see that they get awarded for meritorious behaviour - like joining PF in the first place - but when you've got them, what can you do with them? Or are they like any other trophy that you put on a shelf to gather dust? I just got one for...
  4. Frabjous

    Where Can I Find a Complete List of Mentors and Advisors on Physics Forums?

    The mentor list in https://www.physicsforums.com/help/mentorforums/ is not complete. Shouldn’t there also be a list of various advisors near here?
  5. J

    Equation that describes positive/negative feedback

    Hi, Curious if there is an expression for a negative feedback system that experiences phase shift. For example, at 0 degree phase shift, the additional gain is 0 because it is fully negative feedback. At 180 phase shift the additional gain is infinite because you have full positive feedback. Is...
  6. A

    I need feedback on MCQ test in IJSO style

    Solutions are also attached as a file
  7. A

    I need help with the website -- where should I post these threads?

    I like creating physics and chemistry problems and i want some feedback on them. What is the most appropriate forum to post them and ask for oppinions?
  8. J

    I JC Model in Python: Advice & Feedback Needed - Jon Poplett

    Good afternoon! I am fumbling my way through setting up a JC model in python, I was hoping I could get some feedback on it please. I just want to make sure everything looks good and the data I am collecting is valid. Any advice or feedback would be very welcome...
  9. curiousPep

    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...
  10. A

    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...
  11. mark_bose

    How to explain the effect of temperature profile on feedback coefficient?

    Hi all, I'm trying to derive fuel temperature coefficient in a TRIGA reactor using a monte carlo code. When i do that, if i assume a radial temperature profile along the core, i obtain smaller value (-7pcm/K) than the one achieved with uniform temperature (-9pcm/K). More in detail: in my case...
  12. P

    Engineering Finding out the input impedance in a negative feedback op-amp

    In this case, there is negative feedback. ##V_{out}## is almost equal to ##V_{in}## in this case. But I really can't understand how to even proceed to find out the input impedance in this case, from the equation I know. Can someone help me out in figuring how should I proceed?
  13. S

    Feedback and "Advertisements" do not work

    I am still trying to find somewhere to post to report this problem. If try to visit and post in Feedback, or if I try just to VISIT the "Advertisements" topic there, the only page that loads is this: "Page could not be loaded,... " and I cannot even post the whole page message here because...
  14. PainterGuy

    Engineering State feedback gain for observer/estimator

    For the state equations given above calculate state feedback gain k so that the state feedback system has -1 and -2 as its poles. Then, find TF from r to y for the given state feedback system. Then create a 2 dimensional estimator where the poles of estimator are -2±2j. Finally calculate TF from...
  15. Eclair_de_XII

    LaTeX Feedback on my LaTeX code please

    \newcommand\func{\(f\)} \newcommand\myset[1][math]{\ifthenelse{\equal{math}{#1}}{\(K\)}{K}} \newcommand\diff[4]{\(|#1-#2|#4#3\)} \newcommand\ball[3]{\diff{#1}{#2}{#3}{<}} \newcommand\Fllab[2]{\diff{f(#1)}{f(#2)}{\epsilon}{\geq}} \newcommand\term[2][n_k]{\({#2}_{#1}\)}...
  16. M

    I Checking for negative feedback in a circuit

    This is the circuit in question. During lecture, when checking whether this was negative feedback, my instructor said that if the v_out increases, then v- increases as well, which would lead to the next v_out decreasing because v_out = A(v+ - v-). I get how if v- increases the next v_out would...
  17. J

    Electronics Designing a buck converter with feedback and a regulated output

    I had a bunch of questions regarding the feedback component as well as the feedback mechanism itself. 1. I am using the attached schematic as reference for my design. As per the LM2576 module data sheet, it can handle a maximum current of 3 A whereas I need the IC to handle at least 15 A...
  18. Ntip

    Feedback controller design for boost converter

    I recently started looking into a boost converter design that would be no load most of the time which causes it to operate in DCM. After calculating the duty cycle D, it is dependent on Vi, Vo, L, f, and R. The load R and output voltage Vo are fixed, but I would like to vary the other parameters...
  19. joey13

    Could electricity power a rocket? Feedback appreciated!

    Hi! I'm a high school physics student. I really, really love physics, especially rocket science, and I had an idea about a rocket design, but I don't know how feasible it is. I was hoping you guys could give me some feedback. So I was learning about electricity, and as far as I know, electric...
  20. Jy158654

    How does the negative feedback amplifier below work?

    The book says that " The op-amp multiplies the potential difference between V+ and V- by the open-loop voltage gain to produce Vout." So my first question is, since we say we assume open-loop voltage gain is infinite, so does that mean the Vout produce will be infinite too? Then, the book says...
  21. Nick-stg

    I Interactive Spacetime Diagrams: Get Feedback on What I Built

    I built the tool initially for myself to better understand how Lorentz Transforms and spacetime diagrams work. Then while trying to discuss it with a friend I need to put it online and it snowballed from there. Now I am wondering whether there is any value for others in what I have created...
  22. tanaygupta2000

    What is the effect of feedback on input and output impedances?

    I know that when the feedback is connected, the voltage gain changes by the above formula. But I don't know how to find final values of input and output impedances.
  23. Kaguro

    I Understanding Op-Amp negative feedback

    In an op-amp with negative feedback, say initially the + input has some small positive value and the - input is at 0. Then the op-amp amplifies this difference, and a part of it is fed to the - terminal through resistances. This will increase - and will lessen the difference. My question is...
  24. B

    PID loop with a different command and feedback units / types

    I have a laser and I am adjusting it's position using a motor, and I am reading the laser light intensity at the top and bottom using a sensor. then I divide the top from the bottom and the goal is to get around 0.97%. This is called delta, if delta is too high, you move the motor lower and if...
  25. J

    Oscillator Frequency of a Ring Oscillator with RC feedback

    I'm not sure how will this oscillator work. Assume A is low, so B will be high and the capacitor will charge through B-C- 2Mohm. Now even D has gone high, so A will be high and B will be low and C will discharge. I'm not sure how the voltage divider rule across RC will take into effect. I found...
  26. Z

    Admissions Masters degree letter of motivation feedback.

    This is my motivation letter for the university of Regensburg (Masters). The bad thing is that my grades are above average, not great. And I have little to no research experience due to my BSc school. I avoided useless mumbo-jumbo and flatter so it's going to be short and to the point. I pushed...
  27. J

    Determine the required value of feedback (H) to control the heater output

    Just need a bit of guidance to make sure that I am heading the right way. Question is: Fig 3 shows the block diagram of the control of an electric heating system. The heater is driven from a voltage-controlled power supply, the voltage V1 being derived from a potientiometer. The output...
  28. W

    Linear Feedback Shift register of size 2^7

    From this table: Looking at the 7 row and taking the first entry, 1 This is 000001 Adding back the highest and lowest bit: 10000011 And then the equation would just be x^7 + x +1 ? Or taking the taking the third entry, 7 This is 000111 Adding back the highest and lowest bit: 10001111 And...
  29. C

    Understanding Negative Feedback Systems: Equations, Dynamics, and Activation

    We express such equations by $$\frac{dx}{dt} = \beta - \gamma \cdot x$$, t denotes the time. In this case, γ depends on x, thus the dynamic equation should probably be: $$\frac{dx}{dt} = \beta - \gamma(x) \cdot x$$ 1. Setting the equation to 0 leads to two different cases: If x < K: xST = γlow...
  30. W

    Root Locus of Negative Feedback System

    From my understanding, the root locus is only concerned with open loop gain. I figured this means you would ignore the negative feedback loop and calculate the root locus from just the plant's function Workings: zeros: -1 poles: 0, -2, -2, relative degree = 2 => 90-degree asymptotes meeting...
  31. K

    Calculating controller gain in a feedback loop

    Homework Statement FIGURE 3 shows the block biagram of the control of an electric heating system. The heater is driven from a voltage-controlled power supple, the voltage V1 being derived from a potentiometer. The output temperature, θo is subject to distrubances, θd, because of changes in...
  32. Philip Dhingra

    I Feedback Requested: Special Relativity Simplified by Phil

    I took a stab at simplifying Special Relativity, but I want to be 100% sure I'm not butchering physics in the process. Anybody care to weigh in on that? Here is a draft of my Medium article: https://medium.com/@philipkd/special-relativity-explained-with-a-deck-of-cards-f99bfd873bd5 Thanks, - Phil
  33. kolleamm

    Electromagnetic physical force feedback

    I want to create a small pad consisting of two electromagnets that repel and attract each other, this can give the feeling that something is pushing up against your skin if held. Is this a practical idea?
  34. C

    Understanding the Ideal Op-Amp Negative Feedback Loop

    Homework Statement Hi, Here is what I know about the Ideal Op-Amp. - The open loop voltage gain is infinite - The output voltage is given by the following $$v_o = A(v_+ - v_-)$$ - Only with a negative feedback loop is $$ v_+ = v_-$$ My query is with regards to the negative feedback loop...
  35. F

    Looking for feedback on selecting a good topic

    Homework Statement Choose a technology such as MP3 players, laser, medical imaging, or another that interests you (Other than the cell phone). Research the internet and find out how it is related to the physics of light and waves. In approximately 100-150 words, write a paragraph explaining the...
  36. F

    Examination project of EEG, Opinions and feedback

    Hello! I don't really know how High School ends in other countries but in Sweden it ends with an examination project depending on the programme you've selected. Anyhow we were free to choose one research topic that is related to mathematics, physics, biology and chemistry. I choose the brain...
  37. D

    Differential Amplifier with negative feedback

    Homework Statement [/B] Homework Equations Adiff(single-ended)= 1/2gm*ro||Rd β=R2/(R1+R2) The Attempt at a Solution I am really confused as to how to find A. I know the feedback of the circuits around the R2 and R1, but I don't understand how the open loop gain can be found. Can someone...
  38. ADDA

    Conditional Digital Feedback; is it a good Idea? (Neural Networks)

    In this example: The input multiplier to the artificial neural network, at the bottom of the screen, for each note is determined by an output of an Expectation Maxamazation sequence that converges after ten iterations with input of the artificial neural network's output above a threshhold...
  39. F

    How a positive Feedback Amplifier works?

    In a positive feedback amplifier, as I understand, output of the amplifier is fed back into the input of amplifier, essentially creating a loop. My question is specifically, how the loop does not go in an infinite cycles ? what prevents it from going into an infinite loop ? How many cycles...
  40. mister mishka

    Art My Video Art (fractals, video feedback loops, etc)

    Hey, I just thought I would share some of my video art. They are meant to be visuals going alongside Techno / House music in the nightclubs of Berlin. However I got a lot of ideas from reading up on physics, like diffraction patterns, fractals, polarization of light / materials, lenses, video...
  41. Johny Boy

    A Using feedback in quantum measurements

    If we consider an efficient measurement performed on a system in a pure state. How would we use feedback (by applying to the system a unitary operator that depends upon the measurement result), to prepare the system in the same final state for every outcome of the measurement (this can be done...
  42. Sundog

    Is My Rope Bridge Design Safe? Seeking Feedback on My Plans

    I'm designing a rope bridge that will span around 40 ft over a pond. First off, I know its not recommended to build a bridge like this without having it designed by a professional. However, I plan on overbuilding it and it will not be very high. I'm also thinking about using 3 or 4 ropes to...
  43. N

    MATLAB I with matlab designing a steady state feedback H2 control system

    Hi everyone. I'm designing a steady state feedback H2 control system. Actually, my major is tribology and I have no experience in designing control system. So it is really big problem for me. Anyway, this is my simple model of tribometer which applies normal load on the surface. (is it...
  44. BillTre

    Can Tactile Finger Feedback Enhance Virtual Reality Experiences?

    A http://www.sciencemag.org/news/2017/04/finger-devices-let-users-touch-objects-virtual-reality?utm_campaign=news_daily_2017-04-25&et_rid=33537079&et_cid=1293290 in Science magazine describes two new (to me) approaches to providing tactile feedback to fingers.
  45. B

    Can I acquire the shaft position of my motor using my VFD

    The project I am working on is to design the control system for a shock dynamometer. I am using Labview and communicating to the VFD using Modbus. The shock dyno will look a little something like this; So one of the main objectives in my project is to produce a plot as seen below; The...
  46. The Maker

    I want professional feedback on my work -- Building Model Structures

    Hello, I am The Maker. I am here because I want professional feedback on my work. I have been building things with K'NEX and popsicle sticks since I was little and as a future engineer, I wanted real engineers to evaluate my potential. Please be honest, I am trying to improve my engineering...
  47. Alaguraja

    What's the feedback for an op amp?

    What's the feedback for an op amp? And tell me the formula.
  48. F

    A question regarding electronic negative feedback

    I have a confusion understanding one of the basic assumption used for operational amplifiers which is Vin = 0 or difference of inputs = 0. Take for example an ideal amplifier with inputs V+ and V- V+ = 1 V- = 0.5 * Vout Supply Voltage = +-9 Vin = V+ - V- At start V+ = 1 and V- = 0, providing us...