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Automation
and control
Dr. Salman Hussain
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What is an Op-Amp? – The
Surface
 An
Operational Amplifier (Op-Amp) is
an integrated circuit that uses
external voltage to amplify the input
through a very high gain.
 We recognize an Op-Amp as a massproduced component found in
countless electronics.
What an Op-Amp looks
like to a lay-person
What an Op-Amp looks
like to an engineer
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Applications of Op-Amps
Filters
Low pass filter
Types:
•Low pass filter
•High pass filter
•Band pass filter
•Cascading (2 or more filters connected
together)
R1
Low pass filter transfer
function
+
Low pass filter
Cutoff frequency 
C
R2
+
+ Vcc
- Vcc
+
V0
__
Applications of Op-Amps
 Electrocardiogram


(EKG) Amplification
Need to measure difference in voltage from lead 1
and lead 2
60 Hz interference from electrical equipment
Applications of Op-Amps
 Simple

EKG circuit
Uses differential
amplifier to cancel
common mode
signal and amplify
differential mode
signal
 Realistic


EKG circuit
Uses two noninverting amplifiers
to first amplify
voltage from each
lead, followed by
differential amplifier
Forms an
“instrumentation
amplifier”
Strain Gauge
Use a Wheatstone bridge
to determine the strain of
an element by measuring
the change in resistance
of a strain gauge
(No strain) Balanced
Bridge
R #1 = R #2
(Strain) Unbalanced
Bridge
R #1 ≠ R #2
Strain Gauge
Half-Bridge
Op amp used to
amplify output from
strain gauge
Arrangement
R + ΔR
+
-
Vref
Rf
R
+
R
+ Vcc
- Vcc
+
V0
R - ΔR
Rf
Using KCL at the inverting and noninverting terminals of the op amp we find
ε ~ Vo = 2ΔR(Rf /R2)
that 
__
Applications of Op-Amps
 Piezoelectric
Transducer
 Used
to measure force, pressure,
acceleration
 Piezoelectric crystal generates an electric
charge in response to deformation
 Use
Charge Amplifier
 Just
an integrator op-amp circuit
PID Controller – System Block
Diagram
P
VSET
VERROR
I
Output
Process
D
VSENSOR
Sensor
•Goal is to have VSET = VOUT
•Remember that VERROR = VSET – VSENSOR
•Output Process uses VERROR from the PID controller to
adjust Vout such that it is ~VSET
VOUT
Applications
PID Controller – System Circuit Diagram
Signal conditioning allows you to
introduce a time delay which
could account for things like
inertia
System to
control
Calculates VERROR = -(VSET + VSENSOR)
-VSENSOR
Source:
http://www.ecircuitcenter.com/Circuits/op_pid/op_
Applications
Adjust
Change
PID Controller – PID Controller Circuit
Kp Diagram
RP1, RP2
Ki
Kd
VERR
RI, CI
RD, CD
VERR PID
Applications
of
Op-Amps
 Example of PI Control:
Temperature Control

Thermal System we
wish to automatically
control the
temperature of:

Block Diagram of
Control System:
Applications of Op-Amps
• Example of PI Control: Temperature Contro
 Voltage
Error
Circuit:
 Proportion
al-Integral
Control
Circuit:
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