Feedback control for system tuning
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Transcript of Feedback control for system tuning
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Feedback Control for System
Tuning
Cody Rioux - @codyrioux
Real-Time Analytics - Insight Engineering
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Overview
● Feedback Control
○ Definition
○ Conceptual Model
● Concepts
○ Math
○ Rules of Thumb
● Case Study
○ Controlling Chris’ Effective Hours
● Recap
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Controlling dynamic systems through continuous feedback.
Feedback Control
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What is Feedback Control?
A form of Process Control for
controlling the behavior of black
box systems.
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Cody EngineAccelerator Speed
Whats a
setpoint?
If you drive like me...
No regard for the speed limit, you’re just a feed-forward automaton.
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You (Driver) Engine (V8)Accelerator Speed
Speedometer
Speed Limit
Driving A Car
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Cruise Control Engine (V8)Accelerator Speed
Speed Reading
Speed Limit
What if we got a machine to do it?
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SystemInput Output
A Conceptual Model
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Controller SystemInput OutputSetpoint
A Conceptual Model
This happens to be a feed-forward system.
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Controller SystemInput Output
Feedback / Error
Setpoint
A Conceptual Model
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Controller SystemInput Output
Feedback / Error
Setpoint
A Conceptual Model
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Controller SystemInput Output
Feedback / Error
Setpoint
A Conceptual Model
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Controller SystemInput Output
Feedback / Error
Setpoint
A Conceptual Model
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Controller SystemInput Output
Feedback / Error
Setpoint
A Conceptual Model
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Controller SystemInput Output
Feedback / Error
Setpoint
A Conceptual Model
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Feedback Principle
Continuously compare the actual
output to its desired reference value;
then apply a change to the system
inputs that counteracts any deviation of
the actual output from the reference.
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You’ll need an advanced math degree for these...
Concepts
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Controller SystemInput Output
Feedback / Error
Setpoint
A Conceptual Model
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error = setpoint - output
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input = gain * error
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Things to keep in mind...
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Gain controls the
magnitude of our
adjustments. This is
important.
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Univariate feedback is
inherently simple,
multivariate feedback
inherently complex.
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Prefer small and
frequent adjustments to
large infrequent
adjustments.
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Oscillation creates
instability. We don’t like
that.
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End-to-end control system for maximum analytics productivity.
Case Study: Controlling Chris’
Caffeine Intake
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What if this were...
● … a timeout value?
● … a queue size?
● … a server cluster size?
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We can keep Chris rolling at 8 hours a day 365 if we wanted to.
Recap
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Benefits of Feedback Control
● Automatic - No Need for Analytical Model
● Dynamic - System responds to change
● Real Time - Change Happens Fast
● Self-Correcting - Mistakes are Quickly Corrected
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Feedback control is a viable
solution for configuring
systems under dynamic
conditions.
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Only Scratching the Surface
● Integral Controllers
● Derivative Controllers
● PID Controllers
● Statistical Process Control
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Literature
Feedback Control for Computer
Systems (Janert, 2013)