4-Signal conditioning -Part2


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Sensors & Actuators
Dr. Hassan SHARABATY
BY
Aleppo – March 2012
Department of Mechatronics Engineering
EEM304 Mechatronics
4- Conditioning circuits – Part2
Dr. Hassan SHARABATY Sensors & Actuators – Conditioning circuits 2 2/6
Differential Bridge Conditioning Circuit
in
S S
S V
R R
R
E  








2
1
1 2
2
0






  
  
R R R
R R R
S S
S S
2 0
1 0
2 0
0
S
in
R
V R
E

 
Resistive Sensor
in
S
S S V
R
R R R

  

0
0 0
2
Ex: Position and displacement sensors
Dr. Hassan SHARABATY Sensors & Actuators – Conditioning circuits 2 3/6
;
2 1 2
1 2
0 C C
V C C
E in


  








1 2 0
1 2
d
X
C C
C C
2 0
0 d
V X
E in  
+
= ( )
= ( )
C C  C C C 2 0 1 0 C ,
Differential Bridge Conditioning Circuit
Capacitive Sensor
Ex: Pressure sensors
Dr. Hassan SHARABATY Sensors & Actuators – Conditioning circuits 2 4/6
[ X = 0 ]  [ Z1 = Z2 = Z0 ]
Z Z Z
Z Z Z
  
  
2 0
1 0
[Z0 = jw L0 ]
0
0 2 Z
V Z
E in 
 
Differential Bridge Conditioning Circuit
Inductive Sensor
[ X >0 ] 
Dr. Hassan SHARABATY Sensors & Actuators – Conditioning circuits 2 5/6
Active Potential Divider Circuit
p p
   
1 1
1 1 2 2
2 1
j R C j R C
j R C
V Em C  

 

 
If ωR2 C2 >>1 , ω R1 C1 <<1
2 2 1 1 2
1
2
1
R C
f
p R C p
 
2
1
m C E
C
C
V   
+
Active Potential Divider Circuit
Frequency response
 Impedance Converter
 Conditioning circuit (C & R sensors).
1
2
m C E
Z
Z
V   
1
,
1
2 2
2
2
1
1 1
1 j R C
R
Z
j C
j R C
Z
 





Dr. Hassan SHARABATY Sensors & Actuators – Conditioning circuits 2 6/6
Problem 1:
Using a capacitive humidity sensor whose transfer function is given as
; α% is relative humidity.
1- Design a digital relative humidity meter α=[0,100]%.
2- Draw the frequency response.
(1 ) 0   c c C C
C C F c c 

; 1
0 0  

Dr. Hassan SHARABATY
Sensors& Actuators -Conditioning circuits 2
7/6
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