What is an OpAmp? – The Surface. An Operational Amplifier (OpAmp) is an integrated circuit that uses external voltage to amplify the input through a very high gain. We recognize an OpAmp as a massproduced component found in countless electronics. What an OpAmp looks like to a layperson.
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What an OpAmp looks like to a layperson
What an OpAmp looks like to an engineer
Positive Power Supply
Inverting Input

Output
+
NonInverting Input
Negative Power Supply
Forward Gain
A
Input
Output
β
Feedback
G = Vout/(V+ – V)
Av = Vout/Vin
Vout
Vs+
Vin
Vs
current mirror
current mirror
voltage level shifter
output stage
current mirror
highgain amplifier
differential amplifier
virtualground
If R1 = R2 and Rf = Rg:
Low pass filter
C
R2
R1
+ Vcc

Low pass filter transfer function
+
V0
__
+
 Vcc
+

Low pass filter Cutoff frequency
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
HalfBridge Arrangement
Op amp used to amplify output from strain gauge
R + ΔR
Rf
R
Vref
+ Vcc
+

+
V0
__
+

 Vcc
R
R  ΔR
Rf
Using KCL at the inverting and noninverting terminals of the op amp we find that
ε ~ Vo = 2ΔR(Rf /R2)
PID Controller – System Block Diagram
P
I
VOUT
VSET
VERROR
Output Process
D
VSENSOR
Sensor
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_pid.htm