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. P

    Feedback needed for an oscillator or multivibrator

    i want to ask why the feed back at multivibrator must be positive feedback ?
  2. Planobilly

    Need feedback on this basic grounding schema

    Hi guys, I am trying to find the best way to lay out a grounding system for a typical tube amp. I had in mind to place the filter caps along the HT rail. I can use either axial or radial caps. The issue with the radial caps is they tend to be too big in diameter.I am trying to get to some...
  3. T

    Operational amplifier with feedback problem

    Homework Statement Homework EquationsThe Attempt at a Solution [/B] Using the equations above, I'm not getting the right answer for beta which is 0.4926 V/A. Is my model wrong ?
  4. B

    Do I need a feedback card to acquire motor RPM from a VFD?

    The VFD I plan on using; DURApulse GS3 series AC drive: https://www.automationdirect.com/static/specs/gs3drives.pdf Model: GS3-22P0 The feedback card accessory for the VFD: https://www.automationdirect.com/static/specs/gs3fb.pdf Hi everyone, I would like to know if I need this feedback card to...
  5. F

    Engineering Shunt feedback amplifier circuit

    Homework Statement The attached figure shows a "shunt feedback amplifier" circuit, and its AC equivalent model. Verify that: r_T = \dfrac{v_{out}}{i_{in}}=\dfrac{-R_B}{1+\dfrac{R_B+r_\pi}{(1+\beta)R_C}} (assuming R_B\gg r_e, where r_\pi=(\beta+1)r_e.) Homework Equations In the...
  6. MacLaddy

    Force Feedback control - Capstone project

    I'm attempting to design a force feedback system for my senior capstone project. It will consist of a single lever that is free to move along a single axis. Imagine a video game joystick, but one that only moves forward and back. I need to mimic a given force profile along the stroke of the...
  7. E

    B I would like to get a feedback on this video

    This is a video on Quantum Mechanics that aims to familiarize people with general interests in physics, with some of the main ideas in quantum mechanics. can I get feedbacks on it, I don't have any subscribers at all, and I'd like feedbacks to know how the video could be evaluated. So that's...
  8. marellasunny

    Reliability of low-cost accelerometers in commercial applications

    My question relates to the reliability of low-cost accelerometers (MMA7455,ADXL345 etc.) in commercial products with a expected life expectancy of 5 years or more. The tilt angle reading from the accelerometer will be used as a feedback parameter to orient a single-axis plate-reflector...
  9. R

    Studying Looking for some basic feedback on math book to learn next

    Hello,I started learning math at 29, I went through the high school curriculum in Ontario taking the advanced math courses route. The last book I studied was "nelson calculus and vectors" (Table of Contents)http://www.nelson.com/secondarymath/calculusandvectors/table.html( Curriculum...
  10. JasonHathaway

    Reduce T-Network Feedback Resistance

    Homework Statement Reduce the feedback resistance for the following T-Network Homework Equations Basic circuit analysis (Thevenin maybe?) The Attempt at a Solution My first though was to use Thevenin, and actually I've found some book used that method:
  11. vtechno1729

    Automotive What is a good linear actuator that has force feedback?

    Where can I find one of these? That is, are there linear actuators where I can specify the force it should apply and it gives me back exactly how much force was applied? Are there any linear actuators that can do this and also give me position feedback, i.e., where my object is after it has been...
  12. H

    Schools Please can i get feedback on appeal letter

    To Whom It May Concern:I am writing to appeal my Academic dismissal from the University of Windsor, I was not surprised but very disappointed; I was disappointed in myself because I know that I could have achieved much better results. I would like to urge you to reinstate me for next yearI...
  13. T

    Understanding operation of specific SMPS example (is it a flyback?)

    I don't have much spear time at the moment, but I came across a SMPS diagram in this thread: https://www.physicsforums.com/threads/quick-question-about-inverter-tx-order-wrt-mains.870309/ And I was trying to figure it out, and I don't want to forget about it before I do. So I was wondering if...
  14. S

    Classical Self study project, feedback on my selection of books?

    I'm going to reinforce my physics knowledge via self study in my spare time, the amount of time available is varying since I'm a parent and have a full-time work... My math background: Real and complex analysis, linear algebra (abstract, but finite-dimensional), basic abstract algebra, number...
  15. Marcin H

    Audio Amp with negative feedback

    Homework Statement Homework Equations The Attempt at a Solution I am not really sure how to do this problem. How can I convert from db to linear terms just given db? Don't I need more information? For do I have to do a system of equations or something using the Power gain =...
  16. O

    Electrical position feedback for hydraulic servomechanism

    Homework Statement Assume that you are employed by a company that manufactures hydraulic servomechanisms. You have been asked to recommend an electrical method of providing position feedback rather than the mechanical method used at present (pictured below). The demand signal has been chosen...
  17. KarminValso1724

    Post Paper for Feedback: Is it Safe?

    Or will there be a good chance of it being stolen?
  18. C

    Feedback Request Re U.S. Pat. 9,052,001

    I've recently patented a device which converts high speed rotary motion to slow speed, ultraprecise, high force linear motion using a single, compact moving part. I've just begun the marketing/licensing process but am having trouble getting any useful feedback. If you'd be so kind, please look...
  19. A

    Medical How the homeostatic feedback system would be activated

    Hi All ) i love biology and try to learn about it , i just want to know , . An important aspect of homeostasis is maintaining a normal body temperature. how the homeostatic feedback system that would be activated in response to an elevated body temperature ! Thanks for all info
  20. T

    How does an Op-Amp "find" equilibrium (w/ Negative Feedback)?

    Hi everyone, I've been seeking the answer to this question for a long time. I've looked at posts like... https://www.physicsforums.com/threads/op-amp-transient-state.855512/ and https://www.physicsforums.com/threads/how-does-negative-feedback-in-an-op-amp-work-conceptually.584881/ ...but I...
  21. A

    Identifying type of feedback by looking at bode plot

    Homework Statement Below is the bode plot of return difference, 1+C(S)P(S) in a feedback system. Identify the frequencies where the feedback is large, negative, positive and negligible. P(S) = \frac{100}{s^2+2s+1} C(S) = \frac{220(s+50)}{s+200} Homework Equations Bode Plot, Feedback The...
  22. Justice Hunter

    Exploring the Science of Feedback Loops in Social Media and Beyond

    So I'm trying to exploit the idea of audio feedback and applying it to different Sciences, The one I had in particular in mind is social media. But before I go hammering away at how to exploit it, I need a better understanding of how feedback actually works I believe that the way feedback in...
  23. B

    Engineering Feedback Control: Modeling Mechanical System with Circuit

    Homework Statement Find the transfer function for the following mechanical system with force input fin and output x2. Homework EquationsThe Attempt at a Solution The reason I left the equations blank is because I'm not sure how to appropriately model this scenario. I've seen two different...
  24. TheMathNoob

    Understanding Feedback Loops: Temperature and Forest Area

    Homework Statement I am just wondering if my analysis of the following feedback loops are right. The invariant in this case is Temperature Solar heating->Temperature->Evaporation cloud cover-> albedo->Solar heating Second feedback loop Invariant forest area Forest area->Plant...
  25. W

    Feedback on Practice Exercises

    Hello, I am just looking for some feedback (whether my answers and reasoning is correct) on some practice exercises I am doing. The subject is currently Combinatorics (didn't see a category for that so i just placed this in general math). Problem 1: There are 18 mathematics majors and 325...
  26. A

    Uniformity of thermal vibrations

    Hello, I have a question on the nature of vibrations due to thermal energy. Earlier today I read this article which talked about cooling a glass string to near absolute zero using feedback from a high precision sensor. http://phys.org/news/2015-08-smallest-vibration.html what I understood from...
  27. W

    Engineering Calculate impedance of a feedback circuit with Blackman's technique

    Homework Statement [/B] Calculate impedance of the node shown in this feedback circuit with Blackman and the Vtest/ Itest method. Homework Equations [/B] Zin (with feedback) = Zin(with feedback circuit disabled) * (1-RRshort)/(1-RRopen) RR = return ratio In this form blackman theorem to us...
  28. G

    Question for stability of negative feedback OP-AMP

    Hello. I've studied the golden rules of the feedback OP-AMP and applying this to voltage follower shows that voltage gain (Vout/Vin) is 1. Thus, Vout should eventually follows Vin when Vin suddenly changed. I've tried to follow this process for clear feeling by drawing pictures as shown in the...
  29. O

    Is a Metric Feedback Possible in General Relativity?

    Apologies for not doing too much research prior to asking this question; I suppose actually delving into the mathematics would reveal the answer I'm looking for but I haven't taken the time just yet. Considering the concept of GR where matter/energy tells space how to curve and space tells how...
  30. Joshua McAnaney

    My Theoretical Fusion Reactor- Looking For Feedback

    Ok, so before I begin, I'd like to point out that I'm a 16-year-old GCSE student from the UK. Therefore all of my physics knowledge above high school level is self-taught, so I am by no means an expert. Anyway, I plan on building a deuterium reactor this Summer as a personal project, and I've...
  31. PsychonautQQ

    Trying to understand notes, any feedback is appreciated

    Let 0-->M-->V-->W-->0 be an exact sequence of algebra's. We can then see that W = V/M. (is this true? Wouldn't W = V/Im(M)?) Then i wrote 'codimension 1 in a nilpotent algebra,' no idea why i wrote it. Anyone, if V is a nilpotent algebra, then V^2 < V. Let M be a comdension 1 subspace of V...
  32. I

    Quark confinement potentials -- Feedback requested

    Hello, everyone... I'm starting a new thread (among numerous others) regarding quark confinement and propose a discussion (in case anyone finds it interesting) on some of my considerations. As we all know, the idea of confinement consists in forbidding free propagation of free color-chagres...
  33. A

    Finding the Frequency and Critical Value of a Feedback Amplifier

    Homework Statement Consider a feedback amplifier for which the open loop gain A(s) is given by: A(s) = X/ [(1+s/Y)*(1+s/Z)2] |s=jω Where X = 7500, Y = 90000, and Z = 800000 a) If the feedback factor is independent of frequency, find the frequency at which the phase shift is 180°. b) Find the...
  34. T

    Feedback and equilibrium between black holes and galaxies

    "The supermassive black hole is sucking interstellar gas, but at the same time it is affecting the star-formation history of the galaxy with its powerful winds," Tombesi said. "Astrophysicists describe this process as a feedback between the central supermassive black hole and the galaxy, which...
  35. PrincessIceFall

    Review centre of gravity calculation

    <<Mentor note: Thread merged with duplicate from other forum.>> Half an octagonal prism. A small weight is placed 2 cm from the centreline of the vessel. The rod on which the weight is on is placed at (L/2) i.e at the center of the length of the vessel. The height of center of gravity from the...
  36. Matt Whibley

    Looking for feedback on physics animations

    Hi all I've recently begun developing short (~1 minute) physics animations and would appreciate any constructive feedback. I'm currently uploading them to my Youtube channel here. The purpose of these animations is to work alongside existing teaching. They are not designed or equipped to teach...
  37. D

    How to use current feedback in the same circuit in Cadence

    Hi, I'm currently using cadence virtuoso to design circuit for all-spin-logic device (a kind of spintronics devices). I found in a paper "Circuit Simulation of Magnetization Dynamics and Spin Transport" by Phillip Bonhomme etc. that it can be done using the circuit as follows: They...
  38. Drakkith

    Feedback on a Writing Assignment

    Hey guys. I've got a writing assignment what I'd like to get some feedback on. It's just a little descriptive paragraph, a few hundred words or so. We were supposed to go outside into nature and write a 3rd person description of the setting. No talk of ourselves. What do you think? In the still...
  39. B

    Create a two-stage amplifier without feedback

    < Mentor Note -- thread moved to HH from the technical engineering forums, so no HH Template is shown > Hi, I have a task to create a two-stage amplifier without feedback. It shall be made with these requirements; It shall be connected to a source of internal resistance equal 2.2kΩ and a...
  40. Nicholas moore

    Need feedback for an experiment involving Geiger tubes

    I hypothesize that I can measure an increase in background radiation due to cosmic rays from ground level in Utah to 10,000 ft altitude with a Geiger Muller set-up. I feel that I have enough information to order equipment now (a working knowledge of gm tubes, energy levels of & the special...
  41. D

    Opamp's stabilty in positive feedback

    i simulated the circuits in an mobile app. below is another circuit with negative feedback i understand how the second circuit works(-ve feedback) but the first circuit... here is how the -ve feedback works(i think) we apply 1 volt to inverting input the output keeps falling(since the input is...
  42. K

    Design a Voltage Feedback Loop w/ PID Controller

    Hi Can anybody tell me where to put a PID controller in the picture below to design a voltage feedbaxk loop? Thanks
  43. B

    Pin-screen Matrix feedback

    Hi, This is kind of a hobbyist project or something along those lines. I am trying to build a pin-screen Similar to that, or with whatever conifguration of pins. But I want it to provide electrical feedback so that I can map out where each pin is on a Z-position (their X-Y coordinates are...
  44. Z

    Full State Feedback question

    Below wikipedia page summarizes the full state feedback. Everything is clear but to be able to implement this controller I need to know my states. But What I know is just the A, B and C matrices. So, to be able to simulate this technique on simulink I need to observe the state, I think. Is this...
  45. ranju

    Output Voltage of Feedback Amplifier is 14.85V

    Homework Statement An amplifier without feedback provides an output signal of 15 V with 10% second harmonic distortions when input signal signal is 15 mV. If 1.5% of the output is feedback to the input in a negative series shunt amplifier, what is output voltage?[/B] Homework Equations input...
  46. L

    Op amp with zener in feedback loop

    Getting confused on understanding how opamp works with zener in Feedback loop. Referring to the ckt here (attached.) (replace diode with 5V zener) Using virtual short, when the input voltage is zero, opamp output is 5V? Basically the opamp sources current into the zener. When the input is -1V...
  47. J

    Noise voltage from t-network feedback in opamp circuit

    I'm struggling to compute the noise voltage due to the thermal noise on the resistors of an op-amp circuit, configured as a t-network. If it were a single feedback resistor, the noise voltage referenced to the output (RTO)would be given by sqrt(4KTRB). I'm not sure how to combine them...
  48. J

    How to study feedback? Which branch of Mathematics does it?

    Hello, I want to study a system, and I have realized that all variables in it are dependent. There is no independent variable. So everytime you modify the input, you get an output but at the same time that output modifies the input itself, there is an important feedback. So the system...
  49. R

    ABuild a Feedback Oscillator Circuit & Troubleshoot Frequency Issues

    A circuit is here. I built this circuit. People say a frequency is determined only by tank circuit and C2 is nothing to do with the frequency. But when i change C2 value, the output frequency changes. for example when C2 is 6pF 150Mhz, 12pF 120Mhz 18pF 108 Mhz. why is this happening? i'm...
  50. J

    Amplifiers with Feedback: AC-Analysis and Hybrid-Pie Transistor Model

    I have attached two different amplifiers with feedback, one of them is series-series amplifier and the second one is a shunt-shunt amplifier. AC-Analysis: Using the Hybrid-Pie transistor model • Determine the amplifier parameters Rin, Ro , Mid-band gain A • Determine the low cut-off...
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