true feedback

True Feedback

Putcha V. Narasimham

Knowledge Enabler Systems

Hats off to Pioneers of Feedback

James Watt: Flyball Governor 1788

James C. Maxwell Theory of Governors 1867

Norbert Wiener Cybernetics 1930

H S Black: Feedforward & Feedback Amplifiers 1927

Harry Nyquiat: Stability Criterion 1932

H W Bode : Gain & Phase margins 1940

N Minorsky : PID Controller 1922

Partial list from Lecture Notes Zhiqiang Gao, MIT

25OCT13TRUE Feedback

2

Feedback in Biological & Social Systems

Just beginning to study

Thanks to http://www.linkedin.com/groupItem?

view=&gid=2639211&item=275483709&type=member&commentID=166672173&trk=hb_ntf_COMMENTED_ON_GROUP_DISCUSSION_YOU_FOLLOWED#commentID_166672173

Not aware of all the significant achievements

Got to know Perceptual Control Theory

William T. Powers

(August 29, 1926 - May 24, 2013)

Hats off!


3

This Presentation has Four Sections

This is a companion PPT of PDF

http://www.slideshare.net/putchavn/true-feedback-extended-abstract-pvn-04-jun13

The PDF is not updated….so that may not match this PPT


4

Section

1

Section 2

Section

3

Section

4

http://www.slideshare.net/putchavn/true-feedback-extended-abstract-pvn-04-jun13

Section Contents

Section 1What is Feedback? In depth review; FOUR known elements, Guessing the missing FIFTH element

Section 2Where and how is feedback used? The crucial FIFTH

element, RECEIVER of output.The source of TRUE feedback.

Section 3Complete Feedback System. Receiving Feedback In; Using it

to modify system operation; System Internals; Giving

Feedback Out to supplier. What is mistaken as feedback?

Section 4Examples of working feedback systems; understanding how

& why feedback works; using & making feedback work.

General definition and model.


5

What is Feedback?

In depth review of the concept & its natureAnalysis & Criticism of definitions & diagrams

Understanding FOUR known elementsGuessing the FIFTH vital, missing element


6

Section 1

The Nature & Concept of Feedback

Let’s see the

Best of Top Ten

Googled Definitions

Not the best source but is handy

Is it a stand-alone concept? A monad? Or

A concept built on another concepts, a dyad or triad?

Or a pentad?


7

The Best of Top Ten Googled Definitions

http://www.merriam-webster.com/dictionary/feedback

See my pdf by this name on slideshare

Looks OK, but is it?

See the additional necessary conditions in the next slide

Feedback:

the return to the input

a part of the output

of a machine, system, or process


8

http://www.merriam-webster.com/dictionary/feedback

Graphical Representation of Feedback

Feedback (a triad)

1. Part of Output Xo

2. Returned directly to Input Xi

3. Of the same machine, system or process


9

Output: XoSystem

Input: Xi

Part of Xo returned to Xi, Which part? How is it separated?

Analysis & Criticism of Feedback Definition

Born in practice

Concept & theory: Well developed & perfected

But….

The definition & graphic model are too literal, simplistic & incomplete

Part of output is REDIRECTED, but NOT generated independently

The source of feedback is the system itself--not independent, not external

Can self-generated feedback be VALID?


10

Can Feedback be Self-Generated?

Perhaps,

But it would be too restrictive

Not general Voltage Follower, Special case of feedback

Works here but NOT in general


11

A Xo

Xi-

+

Should Feedback Return To Input?

What is return to input, adding?

Is it valid and general enough?

Is feedback of the same kind as output?

Is there a single input & single output?

Definitions & graphic models

NOT clear & precise

But the practices seem to work

We will see why


12

Something is Missing

The foregoing analysis,

criticism and corrections

are significant

More important is the

missing FIFTH element

Definitions don’t have it


13

1

Input4

Feed

back

3

Output

2

System

5

Missing

The Missing 5th Element is NOT unknown

But is NOT identified and

represented

Let’s find where

feedback arises & goes

Let’s see how it is used


14

1

Input4

Feed

back

3

Output

2

System

5

Missing

End

Sec 1

Where and How is Feedback Used?

Engineering, Biological, Social and Business Systems

Where Feedback Arises and goes

When is Feedback Effective


15

Section 2

Feedback in Engineering Systems

Automatic Control Systems

Adaptive Control Systems

Computer and Communication Systems

Well developed

Comprehensive & Effective

But the Missing element is NOT explicitly identified


16

1Input

4Feed

back

3Output

2System

5Missing

Feedback in Biological Systems

Known to be well evolved, sensitive, adaptive & robust

But…..

Feedback is NOT “mere return of part of the output to input”….

Biological systems show what real feedback is and how it works


17

Feedback is NOT Self Generated

It comes from

External RECEIVER of output

Back to the System

There must be some RECEIVER of the output

Feedback is a special message, sent by the RECEIVER to the System

After using the output

Output and feedback are related but need NOT be of the same kind, often they should NOT be

This is NOT very explicit.


18

Feedback in Social and Business Systems

The fifth element is

Receiver of Output or

Customer

Is explicitly identified & represented


19

Input

Feed

back

Output

System

Customer

The Receiver

of Output

No mistake about it

Completing the Feedback System

Completes the picture

Shows who or what uses Output Xo & generates Feedback In FBin

Separates Xo & FBin

See the next section


20

The FIFTH

element:

Receiver of

output

End

Sec 2

Complete Feedback System

Receiver of Output (Customer)

Generation of Feedback

Feedback Processing by the System

Feedback Out to Supplier of Input


21

Section 3

Receiver of Output Gives Feedback

After using the Output

Back to the System, NOT to Input

Feedback is NOT Output Fed Back

Output & Feedback may NOT be of the same kind


22

3 Xo1 Xi

4 Feedback In

5 R

ece

ive

r(C

ust

om

er)2 System

Feedback Triggers Two System Actions

System1.Modifies its behavior

to generate right output 2 Xo (Not shown)

2.Gives Feedback Out to the Supplier of input 1 Xi

In general both 1 & 2 are necessary


23

2 Xo1 Xi

4 Feedback In 5 R

ece

ive

r

2 System

Feedback Out

To supplier of Xi

Cross Coupling is NOT Feedback

Often mistaken as feedback

It is a special internal connection

Feedback is valid if it is given DIRECTLY to the System---Check

The definition of feedback will be corrected


24

Physical Reaction is NOT Feedback

Reaction is a property of materials and circumstances / conditions

Predicable with fair accuracy

Feedback is the response generated on receipt of stimuli,

Particularly when multiple options of response exist

Not sure if this distinction is rigorous and valid


25

Feedback Should Go To the System

System needs a special

To receive & process feedback

see system internals

Return to input is oversimplified, often infeasible & cannot work

Graphic model is corrected

Definition will be corrected


26

3 Xo1 Xi

4 Feedback

5 R

ece

ive

r(C

ust

om

er)

2 System

Feedback Triggers Two System Actions

1.To control its internal sub-processes & generate right output 2 Xo

2.To give Feedback Out to the Supplier of 1 Xi


27

2 Xo1 Xi

4 FeedbackIn

5 R

ece

ive

r

2 System

Feedback Out

Su

pp

lie

r

System Internals


28

2 Xo1 Xi

4 Feedback In

2 System

Feedback Out

Feedback

Processor

Internal

Control

Generator

Feedback

Generator

2.12.4

2.2

2.3

2.5

Sequence & data

flows--Not shownControls of sub-processes

In coming FB dataOut going FB data

That is the Full Picture of Feedback

It has Five essential elements

System needs Port & Module To receive feedback &

To modify its behavior

System generates & sends Feedback Out to Supplier

We will see examples of how feedback actually works when it works

And how the stated essentials are met


29

End

Sec 3

Examples of Working Feedback Systems


30

Section 4

HOW and WHY Feedback works

Some examples are closely discussed to

See where feedback originates

WHO or WHAT senses feedback

WHO uses Feedback

HOW it is used

WHEN & WHY it works

How feedback propagates to suppler


31

Feedback for effective door-bell operation

1.It should help caller and those at home

2.Call button should be at the entrance door

3.And bell should be where people stay


32

Entrance Door

Door-bell Button

Caller

OE

Ring should reach caller…

1.For him to stop pressing the button

2.And of course those at home to hear and respond


33

Entrance Door

Door-bell Button

Caller

OE

H

Home

Caller needs two kinds of feedback

Caller should know

Bell is ringing &

Some one at home is responding


34

BellSome one

at home Caller

pre

sses

Door-

bell

butt

on

Electrical SigalO

Sound

should

reach

caller’s ear.

Feedback-1Hears the bell and

responds. Feedback-2

Air-conditioner

Air-conditioner Delivers Cooled Air

1.Of Set Temp

2.Output: Cooled Air has two parameters Flow rate F &

Temp To

3.Feedback is Room Temp, Not 2


35

Cool AirDelivery Unit

Set Temp

R Temp

RoomController

FT

Air-conditioner

What feedback does AC need?

1.The Room is the receiver of Cooled Air

2.Something in the room must give feedback of how cool the room is

3.Tempe Sensors (1,2,3.. ) in the room do it


36

Cool Air

Set Temp

R Temp

RoomController

FanCooler Fan

There may be many units in an AC

Multiple Vents for Uniform Cooling

The room may have different temperature zones

May need Multiple vents for uniform cooling


37

Cool Air

Dis

trib

uto

r

Independent Local Vent controls

Each zone may need independent local vent controller

Only one vent is shown


38

Vent 1

ControllerCool Air

Distributor Zone1

Feedback: Temperature SensedSet Point

DistributorZone 1 Local Temp Set Point

Vent 1

Cooled Air Flow rate control signal

Feedback in Driving

While driving ahead

Driver is the Goal Setter,

Feedback Generator &

Controller of car


39

Driver senses Goal

& car position

visually & through

motion

Driver Views & Sets

the Set Points

dynamically

Based on

sensing he

controls the

direction and

speed of his car

Feedback for Reversing the Car

When driver cannot see,

Another person GUIDE

Takes over the control of the car remotely


40

3. Driver reverses the

car as per guide’s

instructions

2 Guide

watches and

gets feedback.

Controls car

remotely

1. Driver can see the

guide but NOT

the rear of

his car

Guide: Remote Driver for Reversing Car

Guide1. Views the gap (goal -- position)

2. Gives reversing instructions

3. Repeats 1 till goal is reached

Guide is the real controller since he gets the feedback

The actual driver merely drives as per guide’s instructions


41

1. Driver can see the

guide but NOT

the rear of

his car

3 Driver merely

follows instructions

2. Guide

The real

controller

(remote)

Feedback in Interactive PPT Drawing

Consider moving objects in PPT 2013, Selected objects are highlighted

Only they move as we drag

Appropriate guide lines appear

For aligning, centering etc.

Give explicit feedback on key parameters

They disappear after positioning the object

Speeds up drawing – Great help


42

Result of User

Feedback? +

Innovation?

Feedback in Interactive Conversation

Human A Human B

Addresses B & gives message M1 Gets M1 & express B’s understanding U1 of

M1 & conveys U1. This is the first feedback

FB1.

Understands U1 in his own way U2

& Checks if U2 is close to intended

meaning of M1 in A’s mind.

If NOT, A modifies M1 as M1A. This

is FB2 on FB1

Gives his understanding of M1A as U3. This is

FB3 on FB2

----------

U3 should be close to intended meaning of

M1. If not, the conversation ends.


43

All this just gets M1 from A to B. See the need and usefulness of feedback

Regulated Voltage Power Supply -- RVPS


44

Current

Io

VoLo

ad

Contr

olle

r

Contr

ollable

Volt

age S

ourc

e R

Vo is fed back

V gen

Set point Vset1. The RVPS delivers power at

2. Constant voltage Vset but variable Current Io

3. Vset is externally set manually

4. Here Vo is fed back (it depends on Io)

Effective Feedback in RVPS


45

Current

Io

VoLo

ad

Contr

olle

r

Contr

ollable

Volt

age S

ourc

e R

Vo is fed back

V gen

Set point Vset 5 When Load, RECEIVER draws Io

6 Vo = Vgen -- Io.R

6 If Vo < Vset, Controller pushes V gen up till Vo=Vset. This happens when Io is high.

7 The revers happens if Vo > Vsetmaintaining Vo at Vset

This works only for Constant Vset

And can NOT deliver constant current if that is what is needed

The set point must set Iset, NOT Vset

What is fed back must correspond to actual current drawn Io by load, NOT output voltage

And the controller has to bring Io back to Iset

And that is NOT ALL!


46

Feedback works Because

The Receiver & User of output generates FB &

Sends it to the right port and module in the System

The System is capable of:1. Receiving FB-in &

2. Processing FB-in

3. Modifying internal behavior

4. Generating FB-Out


47

Special Cases of Simple Feedback

In them output is affected by receiver

So feeding output back works as true feedback

Such feedback is processed suitably to modify the behavior of the system

Feedback Out may not be essential in special cases


48

Effective Feedback is TRUE FEEDBACK

From these examples we find that

TRUE FEEDBACK is used in all effective feedback-controlled systems

1.It is here proposed that

2.All the elements of a feedback system be correctly identified &

3.Used in the definitions and graphic models


49

End

Sec 4

system

The Meaning of the Definition

A & B are parts of the system

A & B are also values of amplification or attenuation factors

Xf is feedback but

NOT TRUE Feedback


50

B

S+

-

XoX = Xi – Xf AX

Xf=Bxo=ABx

A

B returns part of Xo to input

Xi

true feedback

Technology