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
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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!
25OCT13TRUE Feedback
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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
25OCT13TRUE Feedback
4
Section
1
Section 2
Section
3
Section
4
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.
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What is Feedback?
In depth review of the concept & its natureAnalysis & Criticism of definitions & diagrams
Understanding FOUR known elementsGuessing the FIFTH vital, missing element
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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?
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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
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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
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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?
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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
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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
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Something is Missing
The foregoing analysis,
criticism and corrections
are significant
More important is the
missing FIFTH element
Definitions don’t have it
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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
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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
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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
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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
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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.
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Feedback in Social and Business Systems
The fifth element is
Receiver of Output or
Customer
Is explicitly identified & represented
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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
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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
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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
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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
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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
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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
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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
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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
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2 Xo1 Xi
4 FeedbackIn
5 R
ece
ive
r
2 System
Feedback Out
Su
pp
lie
r
System Internals
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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
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End
Sec 3
Examples of Working Feedback Systems
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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
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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
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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
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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
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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
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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
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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
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Cool Air
Dis
trib
uto
r
Independent Local Vent controls
Each zone may need independent local vent controller
Only one vent is shown
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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
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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
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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
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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
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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.
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All this just gets M1 from A to B. See the need and usefulness of feedback
Regulated Voltage Power Supply -- RVPS
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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
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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!
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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
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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
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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
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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
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B
S+
-
XoX = Xi – Xf AX
Xf=Bxo=ABx
A
B returns part of Xo to input
Xi
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