SENSORS and TRANSDUCERS
Tadeusz Stepinski, Signaler och system
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INTRODUCTION
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Course presentation
Classification of transducers
Transducer descriptions
Transducer parameters, definitions and terminology
Transducer effects in silicon and other materials
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SENSORS and TRANSDUCERS
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Course presentation
➤ Classification and descriptions of transducers
➤ Survey of possible energy conversions
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Optical, mechanical, thermal, magnetic and chemical
Sensor characteristics
➤ Sensor compensation
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SENSORS and TRANSDUCERS
SENSORS convert energy information
One energy form must be converted into the same or another
energy form with exactly the same information content as the
originating energy form
Example:
Amplifier
Mic
Loudspeaker
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SENSORS and TRANSDUCERS
SENSORS use some form of energy to get the information
Example: Ultrasonic distance measurement
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SENSORS and TRANSDUCERS
One form of energy can be used for measuring different quantities
Example: Applications of inductive sensors
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SENSORS and TRANSDUCERS
TRANSDUCER - latin tranducere - ‘to convert’
Input transducer - sensor
Output transducer - actuator
TRANSDUCER
Sensor
Biological or
technical
system
Input
F1
Fk
Actuator
Output
Biological or
technical
system
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Classification of transducers
❋ Types
of energy form
Energy domains
Sensors
Electrical system
Radiant
Mechanical
Thermal
Electrical
Magnetic
Electrical
energy
Modifying unit
(A/D or D/A)
Chemical
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Classification of transducers
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Modulating and self-generating transducers
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Modulating transducer requires an auxiliary energy source
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Strain gauge, thermal resistor, liquid-crystal-display
Self-generating transducer requires no auxiliary energy source
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Solar cell, thermocouple, piezoelectric element
X-axis
T
Y-axis
Z-axis
• X-axis input energy domain
• Y-axis output energy domain
• Z-axis modulating energy domain
T
Y-axis
X-axis
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Classification of transducers
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Miller index - three dimensional vector
[x y z] ⇒ [input energy, output energy, modulating energy]
Transducer
Transistor
Thermocouple
pH meter
LED display
LCD display
Coil
Magnetoresistor
Photoconductor
Miller index
[x y z]
[el, el, el]
[th, el, 00]
[ch, el, 00]
[el, ra, 00]
[ra, ra, el]
[ma, el, 00]
[ma, el, el]
[ra, el, el]
Type description
Modulating shape transducer
Self-generating input transducer
Self-generating input transducer
Self-generating output transducer
Modulating output transducer
Self-generating output transducer
Modulating input transducer
Modulating input transducer
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State description of transducers
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The steady state description - reveals characteristics of transducers
Note! No transducer is sensitive to one physical energy only
Consider a small volume dV in which transducer is placed
The energy content dW in this volume contains the summation of all possible energies
dW = ∑ Ii ⋅ei = σ ⋅ dl + P
∂ρ
+ V ⋅ dq + E ⋅ dD + H ⋅ dB + T ⋅ dS + wr
ρ
Ii - intensive quantity (can carry power, e.g., force, pressure, voltage)
ei - extensive quantity (cannot curry power, e.g.,displacement, resistance)
dl - displacement
σ - mechanical force
P - pressure
dρ - volume density of mass
V - voltage
dq- volume density of charge
E - electrical field
dD- charge per unit surface
H - magnetic field
dB - magnetic induction
T - absolute temperature
dS - entropy per unit volume
wr - radiation per unit volume
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Static Characteristics
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Systematic Characteristics
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Range - min and max values of input or output variables
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Span - maximum variation of input or output
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Example: input range 100 -250°C or output range 4 to 20 mA
Example: 150 °C or 16 mA
Linearity - input values I and
output values O lie on a straight
line
Oideal = KI + a
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K=
Omax − Omin
I max − I min
Nonlinearity
N ( I ) = O( I ) − ( KI + a)
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Dynamic Characteristics
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Transfer functions
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First order elements
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Example: Temperature sensor is described by heat balance equation
τ
dT
+ T = TF
dt
⇒ G(s) =
1
1 + τs
where:
τ - time constant
T- sensor temperature
TF- ambient temperature
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Dynamic Characteristics
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Transfer functions
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Second order elements
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Example: Mass-spring-damper (accelerometer)
1 d 2 x 2ξ dx
1
+
+x= F
2
ω n dt
ω n dt
k
⇒ G ( s) =
1
1 2 2ξ
s +
s +1
ω n2
ωn
where:
ωn =
k
m
ξ=
λ
2 km
rad / sec
- undamped natural
frequency
- damping ratio
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Transducer parameters
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The state description - Example
Parameter
Unit
Description
Settling (response) time
Rise time
Excitation
Sensitivity
Hysteresis
Offset voltage
Temperature coefficient
Repeatability
s
s
V or A
dV/dxi
any
mV
ppm K -1
%
Time for signal to respond to step input signal within a rated accuracy
Time for signal to change from 10% to 90% of its p-p value
Power supply voltage/current required for normal operation
The rate of change at the output at the change at the input
Permanent deviation from zero for zero input
Output voltage obtained for zero (reference) input conditions
The rate of change of reading as a function of temperature
Measure of agreement between successive measurement (same
conditions)
Measure of agreement between successive measurement (changed
conditions)
Operating span for specified accuracy
Reproducibility
Temperature range
%
T(K)
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Static errors - error reducing techniques
Compensating non-linear element
Vout = Kk cor Fin
High gain negative feedback
Vout =
Kk A
1
Fin ≈
Fin
kF
1 + Kk A k F
if
Kk A k F >> 1
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Dynamic errors - Compensating techniques
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Open-loop dynamic compensation
Vout (ω ) = Gu (ω )Gc (ω ) Fin (ω )
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Dynamic errors - Compensating techniques
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High gain negative feedback
Vout (ω ) =
G (ω )G A (ω )
1
Fin (ω ) ≈
Fin (ω )
GF (ω )
1 + G (ω )G A (ω )GF (ω )
for
ω min < ω < ω max
G (ω )G A (ω )GF (ω ) >> 1
Accelerometer
KS
∆V ( s )
=
1 2 2ξ S
∆a( s )
s +
s +1
ω ns2
ω ns
ω ns = ω n
ξS = ξ
K AKD KF
k
k
K AKD KF
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Definitions and terminology
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Biophotonics - application of photonic technology in medical or
biotechnology products
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Biosensor
- sensor for the measurements of ion concentrations in living
systems or in organic compounds
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Mechatronics - discipline that combines mechanical and electronic
components into al larger functional unit
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Micromechanics - the design, the development and the production of
extremely small mechanical devices
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Optoelectronics - discipline combining optics or photonics and
electronics on one device
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Smart sensor - single-chip functional unit combining sensing and
processing functions
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Transducer effects in silicon and other compatible
materials
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Transducer effects in silicon - electrons are the information carrier
I/Out
Energy
domain
Radiation
Mechanical
Thermal
Electrical
Magnetic
Chemical
Self-generating
Volta effect, solar
cell
Not known
Seebeck effect,
thermocouple
Thermal energy,
resistance
Maxwell diffused
coil
Galvanic
Modulating
Resistor,
inductance,
capacitive
Photoconductor
Diode
Transistor
Photodiode
Phototransistor
Piezoresistivity
Piezojunction
Piezotransistor
R = f(T)
Electric field
MOSFET
Magnetoresistor
Reverse biased
Irev= f(T)
Electric field
FET
Magnetic diode
Forward biased
UBE= f(T)
Dual gate
MOSFET
Hall effect
Ion concentration
Not known
ISFET
Examples of
smart
transducers
Photo-IC
CCD
Accelerometer
Piezo IC
Temeperature IC
All types of IC
Hall IC
Smart nose
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Review Questions
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Describe difference between modulating and self-generating transducers
Define type and Miller index for
¬
termistor
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TV screen
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Loudspeaker
Give an example of self-generating sensor for thermal energy
Give an example of modulating sensor for magnetic energy
Derive transfer function for a temperature sensor
Derive transfer function for a mass-spring-damper
Describe the principle of compensation using open-loop correction
Describe the principle of compensation using high gain negative feedback for
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static characteristics
dynamic characteristics
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