Returning part of output back to input is considered feedback but this is NOT valid in all cases. This identifies what is missing in a complete FEEDBACK model: The User or Customer of the output. The feedback must come from the User of the output based on using the output. What such user gives is TRUE feedback. Many cases in which feedback works effectively it is because the feedback is TRUE. Such cases are discussed to support this view. Use this and let me know your cases and how you are using TRUE feedback.

1. True Feedback
Putcha V. Narasimham
Knowledge Enabler Systems

2. 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
TRUE Feedback
2
 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
25OCT13

3. Feedback in Biological & Social Systems
 Just beginning to study
 Thanks to
 http://www.linkedin.com/groupItem?
view=&gid=2639211&item=275483709
&type=member&commentID=16667217
3&trk=hb_ntf_COMMENTED_ON_GROU
P_DISCUSSION_YOU_FOLLOWED#comm
entID_166672173
TRUE Feedback
 Not aware of all the
significant achievements
 Got to know
 Perceptual Control Theory
 William T. Powers
 (August 29, 1926 - May 24, 2013)
 Hats off!
25OCT13
3

4. This Presentation has Four Sections
4
 This is a companion PPT of PDF
 http://www.slideshare.net/putchavn/true-feedback-extendedabstract-pvn-04-jun13
 The PDF is not updated….so that may not match this PPT
Section 2
Section
1
TRUE Feedback
Section
3
Section
4
25OCT13

5. Section Contents
5
What is Feedback? In depth review; FOUR known
Section 1 elements, Guessing the missing FIFTH element
Section 2
Section 3
Complete Feedback System. Receiving Feedback In; Using it
to modify system operation; System Internals; Giving
Feedback Out to supplier. What is mistaken as feedback?
Section 4
TRUE Feedback
Where and how is feedback used? The crucial FIFTH
element, RECEIVER of output.The source of TRUE feedback.
Examples of working feedback systems; understanding how
& why feedback works; using & making feedback work.
General definition and model.
25OCT13

6. Section 1
What is Feedback?
In depth review of the concept & its nature
Analysis & Criticism of definitions & diagrams
Understanding FOUR known elements
Guessing the FIFTH vital, missing element
TRUE Feedback
25OCT13
6

7. The Nature & Concept of Feedback
 Is it a stand-alone concept?
A monad? Or
 A concept built on another
concepts, a dyad or triad?
 Or a pentad?
TRUE Feedback
7
 Let’s see the
 Best of Top Ten
 Googled Definitions
 Not the best source
but is handy
25OCT13

8. The Best of Top Ten Googled Definitions
Feedback:
 the return to the input
 a part of the output
 of a machine, system,
or process
TRUE Feedback
 http://www.merriamwebster.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
25OCT13
8

9. Graphical Representation of Feedback
Input: Xi
System
TRUE Feedback
Feedback (a triad)
Output: Xo
1. Part of Output Xo
2. Returned directly
to Input Xi
Part of Xo
returned to Xi,
3. Of the same
Which part?
machine, system or
How is it
separated?
process
25OCT13
9

10. Analysis & Criticism of Feedback Definition
 Born in
practice
 Concept &
theory: Well
developed &
perfected
 But….
TRUE Feedback
 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?
25OCT13
10

11. Can Feedback be Self-Generated?
 Perhaps,
 But it would be
too restrictive
 Not general
TRUE Feedback
Xi
+
A
11
Xo
 Voltage Follower, Special case of feedback
 Works here but NOT in general
25OCT13

12. 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?
TRUE Feedback
12
 Definitions &
graphic models
 NOT clear & precise
 But the practices
seem to work
 We will see why
25OCT13

13. Something is Missing
 The foregoing analysis,
criticism and corrections
are significant
 More important is the
missing FIFTH element
 Definitions don’t have it
TRUE Feedback
13
2
System
1
Input
4
Feed
back
3
Output
5
Missing
25OCT13

14. 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
TRUE Feedback
14
2
System
1
Input
4
Feed
back
3
Output
5
Missing
25OCT13
End
Sec 1

15. Section 2
Where and How is Feedback Used?
Engineering, Biological, Social and Business Systems
Where Feedback Arises and goes
When is Feedback Effective
TRUE Feedback
25OCT13
15

16. Feedback in Engineering Systems
 Automatic Control
Systems
 Adaptive Control
Systems
 Computer and
Communication
Systems
TRUE Feedback
 Well developed
 Comprehensive &
1
Effective
Input
 But the Missing
element is NOT
explicitly identified
16
2
System
4
3
Output
Feed
back
5
Missing
25OCT13

17. Feedback in Biological Systems
17
Known to be
well evolved,  Feedback is NOT “mere return of part of the
sensitive,
output to input”….
adaptive &
 Biological systems show what real feedback is
robust
and how it works
But…..
TRUE Feedback
25OCT13

18. Feedback is NOT Self Generated
 It comes from
 External
RECEIVER of
output
 Back to the
System
TRUE Feedback
18
 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.
25OCT13

19. Feedback in Social and Business Systems
 The fifth
element is
 Receiver of
Output or
Customer
 Is explicitly
identified &
represented
TRUE Feedback
System
Input
Output
Feed
back
The Receiver
of Output
Customer
No mistake about it
25OCT13
19

20. Completing the Feedback System
The FIFTH
element:
Receiver of
output
TRUE Feedback
20
 Completes the picture
 Shows who or what uses
Output Xo & generates
Feedback In FBin
 Separates Xo & FBin
 See the next section
25OCT13
End
Sec 2

21. Section 3
Complete Feedback System
Receiver of Output (Customer)
Generation of Feedback
Feedback Processing by the System
Feedback Out to Supplier of Input
TRUE Feedback
25OCT13
21

22. Receiver of Output Gives Feedback
TRUE Feedback
1 Xi
2 System
3 Xo
4 Feedback In
5 Receiver
(Customer)
 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
25OCT13

23. System
1.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
TRUE Feedback
1 Xi
2 System
2 Xo
Feedback Out
To supplier of Xi
4 Feedback In
5 Receiver
Feedback Triggers Two System Actions
25OCT13
23

24. Cross Coupling is NOT Feedback
24
 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
TRUE Feedback
25OCT13

25. Physical Reaction is NOT Feedback
 Reaction is a
property of
materials and
circumstances /
conditions
 Predicable with
fair accuracy
TRUE Feedback
25
 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
25OCT13

26. Feedback Should Go To the System
 To receive & process
feedback
 see system internals
 Return to input is
oversimplified, often
infeasible & cannot work
TRUE Feedback
 Graphic model is corrected
1 Xi
3 Xo
2 System
4 Feedback
5 Receiver
(Customer)
 System needs a special
26
 Definition will be corrected
25OCT13

27. TRUE Feedback
1 Xi
Supplier
1.To control its
internal subprocesses &
generate right
output 2 Xo
2.To give Feedback
Out to the
Supplier of 1 Xi
2 System
Feedback
Out
2 Xo
4 Feedback
In
5 Receiver
Feedback Triggers Two System Actions
25OCT13
27

28. System Internals
1 Xi
2.1
2.3
Controls of sub-processes
2.2
Feedback
Generator
Feedback Out
TRUE Feedback
28
2 System
Internal
Control
Generator
Out going FB data
2 Xo
2.4
Sequence & data
flows--Not shown
2.5
In coming FB data
Feedback
Processor
4 Feedback In
25OCT13

29. 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
TRUE Feedback
29
 We will see examples
of how feedback
actually works when
it works
 And how the stated
essentials are met
25OCT13
End
Sec 3

30. Section 4
Examples of Working Feedback Systems
TRUE Feedback
25OCT13
30

31. HOW and WHY Feedback works
 Some examples are
closely discussed to
 See where feedback
originates
 WHO or WHAT senses
feedback
TRUE Feedback
31
 WHO uses Feedback
 HOW it is used
 WHEN & WHY it works
 How feedback
propagates to suppler
25OCT13

32. 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
TRUE Feedback
Caller
Entrance
Door
O
Door-bell
Button
E
25OCT13
32

33. Ring should reach caller…
Caller
Entrance
Door
O
Door-bell
Button
TRUE Feedback
E
33
1.For him to stop
pressing the button
2.And of course those at
home to hear and
respond
25OCT13

34. Caller needs two kinds of feedback
TRUE Feedback
presses Door-bell
button
Caller
 Caller should
know
 Bell is ringing &
 Some one at
home is
responding
O
34
Electrical Sigal
Sound
should
H
reach
caller’s ear.
Feedback-1
Bell
Some one
at home
Home
Hears the bell and
responds. Feedback-2
25OCT13

35. Air-conditioner Delivers Cooled Air
Air-conditioner
Delivery Unit
Set
Temp
T
Cool Air
Room
R Temp
TRUE Feedback
1. Of Set Temp
2. Output: Cooled Air has
two parameters
 Flow rate F &
 Temp To
F
Controller
35
3. Feedback is Room Temp,
Not 2
25OCT13

36. What feedback does AC need?
Air-conditioner
Cooler
Cool Air
Fan
Fan
Set Temp
Controller
Room
R Temp
36
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
There may be many units in an AC
TRUE Feedback
25OCT13

37.  The room may
have different
temperature
zones
 May need
Multiple vents
for uniform
cooling
TRUE Feedback
Cool Air
Distributor
Multiple Vents for Uniform Cooling
25OCT13
37

38. Independent Local Vent controls
 Each zone
may need
independent
local vent
controller
 Only one vent
is shown
TRUE Feedback
Flow rate control signal
Cooled Air
Vent 1
Cool Air
Distributor
38
Vent 1
Controller
Zone1
Feedback: Temperature Sensed
Set Point
Distributor
Zone 1 Local Temp Set Point
25OCT13

39. Feedback in Driving
 While driving ahead
 Driver is the
 Goal Setter,
 Feedback Generator &
 Controller of car
TRUE Feedback
39
Driver Views & Sets
the Set Points
dynamically
Driver senses Goal
& car position
visually & through
motion
Based on
sensing he
controls the
direction and
speed of his car
25OCT13

40. Feedback for Reversing the Car
40
1. Driver can see the
 When driver cannot see,
 Another person GUIDE
 Takes over the control of
the car remotely
TRUE Feedback
2 Guide
watches and
gets feedback.
Controls car
remotely
guide but NOT
the rear of
his car
3. Driver reverses the
car as per guide’s
instructions
25OCT13

41. Guide: Remote Driver for Reversing Car
 Guide
1. 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
TRUE Feedback
2. Guide
The real
controller
(remote)
1. Driver can see the
guide but NOT
the rear of
his car
3 Driver merely
follows instructions
25OCT13
41

42. Feedback in Interactive PPT Drawing
42
 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
TRUE Feedback
Result of User
Feedback? +
Innovation?
25OCT13

43. Feedback in Interactive Conversation
Human A
43
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.
All this just gets M1 from A to B. See the need and usefulness of feedback
TRUE Feedback
25OCT13

44. Regulated Voltage Power Supply -- RVPS
Set point Vset
TRUE Feedback
Load
R
Controller
Controllable
Voltage Source
V gen
1. The RVPS delivers power at
Io
2. Constant voltage Vset but
variable Current Io
3. Vset is externally set
manually
Vo
4. Here Vo is fed back (it
depends on Io)
Current
Vo is fed back
25OCT13
44

45. Effective Feedback in RVPS
R
TRUE Feedback
Controller
Controllable
Voltage Source
V gen
5 When Load, RECEIVER draws Io
Current
6 Vo = Vgen -- Io.R
Io
6 If Vo < Vset, Controller pushes
V gen up till Vo=Vset. This
happens when Io is high.
Vo
7 The revers happens if Vo > Vset
maintaining Vo at Vset
Load
Set point Vset
45
Vo is fed back
25OCT13

46. 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
TRUE Feedback
46
 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!
25OCT13

47. Feedback works Because
 The Receiver &
User of output
generates FB &
 Sends it to the
right port and
module in the
System
TRUE Feedback
47
The System is capable of:
1. Receiving FB-in &
2. Processing FB-in
3. Modifying internal behavior
4. Generating FB-Out
25OCT13

48. Special Cases of Simple Feedback
48
 Such feedback is
 In them output is
processed suitably to
affected by receiver
modify the behavior of the
 So feeding output
system
back works as true
 Feedback Out may not be
feedback
essential in special cases
TRUE Feedback
25OCT13

49. Effective Feedback is TRUE FEEDBACK
49
 From these
1.It is here proposed that
examples we find
2.All the elements of a
that
feedback system be
 TRUE FEEDBACK is
correctly identified &
used in all effective
feedback-controlled 3.Used in the definitions
and graphic models
systems
TRUE Feedback
25OCT13
End
Sec 4

50. The Meaning of the Definition
Xi
+
S
X = Xi – Xf
-
A
AX
system
Xf=Bxo=ABx
B
B returns part of Xo to input
TRUE Feedback
50
 A & B are parts of
Xo the system
 A & B are also values
of amplification or
attenuation factors
 Xf is feedback but
 NOT TRUE Feedback
25OCT13