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ELECTRONIC INSTRUMENTATION
EKT 314/4
WEEK 5 : CHAPTER 3
SIGNAL CONDITIONING
Chapter 3 Problem Statement
 Don’t know why signal conditioning needed.
 Don’t know where should the signal conditioning part to be
located.
 Don’t know what actually the content of signal conditioning
part.
 Don’t know what the function of signal conditioning parts.
Chapter 3 Objectives
 To understand why signal conditioning is important
 To know where exactly signal conditioning circuit exist
 To implement amplifier, modulator and filter circuit in
system
 To suit each circuit to system implementation
Chapter 3 Content
 Introduction
 Signal Conditioning Circuit (SCC) Function
 Preliminary Requirement
 Signal Conditioning (SC) System Type
 Amplifier
 Modulator
 Filter
Chapter 3 Content
 Introduction
 Signal Conditioning Circuit (SCC) Function
 Preliminary Requirement
 Signal Conditioning (SC) System Type
 Amplifier
 Modulator
 Filter
Introduction
SCC Function
Perform Linear Task/Process
2. Perform Non-Linear Task/Process
1.
Chapter 3 Content
 Introduction
 Signal Conditioning Circuit (SCC) Function
 Preliminary Requirement
 Signal Conditioning (SC) System Type
 Amplifier
 Modulator
 Filter
SCC Function
Perform Linear Task/Process
1.
›
›
›
›
›
›
2.
Amplification
Attenuation
Integration
Differentiation
Addition
Substraction
Perform Non-Linear Task/Process
SCC Function
Perform Linear Task/Process
2. Perform Non-Linear Task/Process
1.
›
›
›
›
›
›
›
Modulation
Demodulation
Sampling
Filtering
Clipping & Clamping
Squaring & Linearizing
Multiplication
Chapter 3 Content
 Introduction
 Signal Conditioning Circuit (SCC) Function
 Preliminary Requirement
 Signal Conditioning (SC) System Type
 Amplifier
 Modulator
 Filter
Preliminary Requirement
 Passive Transducer
 Require excitation
 Require amplification
 Active Transducer
 Require amplification
Signal Excitation
 Only needed by passive transducer since they cannot
generate their own voltage or current
 Excitation come from external source
 External source can be ac or dc
Chapter 3 Content
 Introduction
 Signal Conditioning Circuit (SCC) Function
 Preliminary Requirement
 Signal Conditioning (SC) System Type
 Amplifier
 Modulator
 Filter
SC System Type
DC Signal Conditioning System
2. AC Signal Conditioning System
1.
SC System Type
1.
DC Signal Conditioning System

2.
Generally used for common resistance transducers (e.g.
potentiometer and straing gauges)
AC Signal Conditioning System


Used for variable reactance transducers
For systems where signal have to be transmitted via long
cables to connect the transducers to signal conditioning
equipment.
DC Signal Conditioning System
AC Signal Conditioning System
Signal Conditioning (SC)
System Type
DC SC System
AC SC System
Chapter 3 Content
 Introduction
 Signal Conditioning Circuit (SCC) Function
 Preliminary Requirement
 Signal Conditioning (SC) System Type
 Amplifier
 Modulator
 Filter
Amplifier
 Two types
 Operational Amplifier (OpAmp)
 Instrumentation Amplifier
Amplifier
 Normal Amplifier
 Block Diagram
 OPAMPs
 Non-Inverting / Inverting
 Integrator / Differentiator
 Sum/Scale/Average
 Substractor
 Comparator
 Instrumentation Amplifier
Amplifier: Block Diagram
Input
Stage
• Dual input
balanced output
differential
amplifer
• Double-ended
high gain amplifier
• Gain = 60
Intermediate
Stage
• Single-ended
differential
amplifier
• Dual input
unbalanced output
differential
amplifier
• Gain = 30
Level
Shifter
• Level translator
circuit
• To bring dc output
voltage to ground
potential
Output Stage
• Push-pull
complementary
amplifier
• Gain = 5 to 10
OPAMPs
 Vo = AVid = A(V+ - V-)
 A – Large signal voltage
gain
 Vid – differential input
voltage
 V+ - noninverting terminal
voltage
 V- - inverting terminal
voltage
OpAmp Operation
 Non-Inverting
 Scaling Amplifer
 Inverting
 Averaging Amplifier
 Integrator
 Substractor
 Differentiator
 Comparator
 Summing Amplifier
Non-Inverting Amplifier
 Key: Input signal is applied to the
non-inverting input terminal.
 Vo  V   V  0 

  

 RF   R1 
V  Vin
Vo Vin Vin


RF RF R1
1
Vo
1 

 Vin  
RF
 R1 RF 
 R 
Vo
 AF  1  F 
Vin
R1 

Inverting Amplifier
 Key: The input signal is applied to
the inverting terminal.
Vin  V V  Vo

R1
RF
V  V  0
Vin
Vo

R1
RF
Vo
RF
 AF  
Vin
R1
OpAmp as Integrator
OpAmp as Integrator
 Key: Use CF instead of RF
I in  I f
Vin  V
dV
 CF C
R1
dt
Vin  V
d (V  Vo )
 CF
R1
dt
V  V  0
Vin
dV
 C F o
R1
dt
t
t
Vin
dVo


C
F
0 R1
dt
0
t
1
Vo  
Vin dt
C F R1 0
Practical Integrator Circuit
 At low freq and dc signal,
CF acts like an open circuit
 Close loop gain = open
loop gain
 Produce too much output
offset voltage.
Practical Integrator Circuit
 At zero freq (DC) and
without negative feedback,
the circuit treats the input
offsets as a valid input
signal charges the
capacitor.
 This drive the output into
+ve or –ve saturation.
Practical Integrator Circuit
 Insert RF in parallel with
CF
 Resistor, RF used must be
at least 10 times the input
resistance, R1
Integrator Application
 To use constant input voltage to produce a ramp voltage
 Analog Computer
 A/D Conversion
 Signal Wave Shaping
OpAmp as Differentiator
OpAmp as Differentiator
 Key: Input resistor replaced by
capacitor
Ic  I f
C1
dVc V  Vo

dt
RF
C1
d (Vin  V ) V  Vo

dt
RF
V  V  0 because A 
C1
dVin
V
 o
dt
RF
Vo  C1 RF
dVin
dt
Practical Differentiator Circuit
 This differentiator has
tendency to undesirably
oscillate
 The gain RF/XC1 increases
at a rate of 20dB/decade
with increases in frequency
 become unstable
Practical Differentiator Circuit
 As the freq increases, input
impedance XC decreases,
making the circuit more
susceptible to high
frequency noise.
 This noise is superimposed
after amplification, on the
differential output signal.
Practical Differentiator Circuit
 Introduce R1 and CF
 0.01RF < R1 < 0.1RF so
close loop gain reduced to
between -10 to -100.
Practical Differentiator Circuit
Consideration:
1. fa is the highest freq
range to be
differentiated
fa = 1/(2RFC1)
Practical Differentiator Circuit
Consideration:
2. fb is the gain limiting
frequency at which the
gain begins to decrease
at a rate of
20db/decade.
fb = 1/(2R1C1)
R1C1=RFCF
fb=20fa
Differentiator Application
 Detection of the leading and trailing edges of rectangular
pulse
 Wave shaping circuit to detect high frequency components in
an input signal.
 Rate of change detector in FM modulators.
 Triggering the time base generator in an oscilloscope.
OpAmp as Summing
 Key: Depends on relation of Ra, Rb,
Rc, RF, circuit can be summing,
scaling or average amplifier.
I a  Ib  Ic  I f  I 
I  0
Va  V Vb  V Vc  V V  Vo



Ra
Rb
Rc
RF
V  V  0
Va Vb Vc
Vo



Ra Rb Rc
RF
Sum, Scale, Average Amplifier
Function
Condition
1 Sum
Ra=Rb=Rc=RF
2 Scale
Ra≠Rb ≠ Rc
3 Average
Ra=Rb=Rc
Scale :
Va Vb Vc
V


 o
Ra Rb Rc
RF
Ra  Rb  Rc
 RF
RF
RF 

Vo   Va 
Vb 
Vc 
Rb
Rc 
 Ra
Sum :
Va Vb Vc
V


 o
Ra Rb Rc
RF
Ra  Rb  Rc  RF
Vo  (Va  Vb  Vc )
Average :
RF 1

R n
R
Vo  (Va  Vb  Vc ) F
R
V V V 
Vo   a b c 
3


Ra  Rb  Rc  R;
OpAmp as Substractor
 Key: All R value are same.
at node V :
Va  V V  Vo

R
R
Vo  Va  2V
at node V :
Vb  V V  0

R
R
V
V  b
2
V  V , Substitute into Vo :
Vo  Va  Vb 
OpAmp as Comparator
 Key: Opamp used without




feedback.
Amplifier goes either to
saturation limit +Vcc or –
VEE
One terminal considered as
reference terminal.
When V+ > V-, Vo 
When V+ < V-, Vo 
OpAmp as Comparator
 If V- = GND, slight V+++
result in Vo = +Vsat =
+VCC
 If V- = GND, V+ goes
slightly below 0, Vo = -Vsat
= -VEE
 Diodes used to protect
opamp from damage due to
excessive Vin.
OpAmp as Comparator
 If Vin feed to V+ then it is
called non-inverting
comparator.
 If Vin fed to V- then it is
called inverting
comparator.
Comparator Application
 Discriminator
 Voltage level detector
 Oscillator
 Digital interfacing
 Schmitt trigger
Amplifier
 Normal Amplifier
 Instrumentation Amplifier
 Important Features
 Difference with Normal Opamp
ELECTRONIC INSTRUMENTATION
EKT 314/4
WEEK 5 : CHAPTER 3
END