1_Sensors

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1.1. Definition

1.3. Classification of Sensors

1.4. Sensor Principles

1.5. Sensors Output Signals

1.6. Passive Sensors

1.7. Stages of Development of a Sensor System

1. Sensors

P. 1-1S. 1-1 Prof. Dr.-Ing. O. Kanoun

Chair for Measurement and Sensor Technology

1.2. Calibration of Sensors

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S. 1-2

1.1 What is a Sensor?

Sensor

[DIN 1319]

Sensor – Part of a measurement equipment that responds to a measurement quantity

Sensor - System, that converts a physical quantity and changes it in a suitable signal

Latin Sensus = The Sensing

Physical Quantity

or Event

Example: A resistance changes with temperatur

Also Sensing Element, Probe, Transducer

Prof. Dr.-Ing. O. KanounChair for Measurement and Sensor Technology

Excitation, Energy

Signal

P. 1-2

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S. 1-3

A Sensor is a Transducer

Measurement Quantity

Environment Energy

Excitation

Energy Supply

Output Signal

Output Energy

mechanical

thermal

magnetic

Radiation

chemical

electrical

thermo electric effect

for temperature

measurement

Current or Voltage

el. resistance

S. 1-3


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Pressure

p el. Field E

Position

l

Resistance

R

Position

l

Capacitance

C

Rotation Speed el. Voltage

U

Temperature

T

Resistance

R

Temperature

T

el. Voltage

U

w

U

A B

Induktionsgesetz

R T R T ( ) ( ) 0 1

(Metalle)

U a T T m v ( )

Thermoelement

Non ElectricalSignal

Analog ElectricalSignal

Principle

Measurement Principle - physical principle in use

S. 1-4 Prof. Dr.-Ing. O. KanounChair for Measurement and Sensor Technology


piezo electric effect

strain sensor

capacitive sensor

P. 1-4

induction

metals

thermo couple

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S. 1-5

Calibration-

To find out the relationship between Input and output quantity

[DIN 1319]

Prof. Dr.-Ing. O. KanounProfessur für Mess- und Sensortechnik

1.2 Calibration

Sensor

Real Value of the

Measurement Quantity Sensor Signal

M1 S1

M2 S2

M3 S3

Mi Si

Calibration Data

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S. 1-6

Possibilities of Calibration

Calibration by Comparisonusing a Precision Device Calibration by usingan Etalon

Etalon Sensor Sensor

Precision Device

S SE

Gn

Measurement

Quantity

Output Value

Real Value Real Value

Output Value


1.2 Calibration

M1 S1

M2 S2

M3 S3

Calibration Data

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S. 1-7

Calibration at a Fixed Point

(Water Triple Point) Calibration by Comparison

Example: Calibration of Thermometers


Vapor

ICE

Water

Thermostat Bath

1.2 Calibration

Tempered Liquid

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S. 1-8

Calibration Hierarchy

CompanyCalibration Certificate

Client

+ Data Scheet

Technical

Requirements

Product

ISO 90XX


1.2 Calibration

National

Etalon

Reference Etalon

Working Standard

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Information Technology

Aspects

- Signal

- System ability

- Signal parameters

Principle

- Resistive

- Capacitive

- Inductive

- Electrochemical

- …

Energy supply

- Active

- Passive

Development Level

- Elementary

- Integrated

- Intelligent

Application

- Automotive

- Environment

- Medicine

- Intelligent home

- Research and development

- …

1.2 Classification of Sensors

S. 1-9 Prof. Dr.-Ing. O. KanounChair for Measurement and Sensor Technology P. 1-9

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1.3 Measurement Principles

Example 1: Resistive Sensors

A

l R

l A

Changes of Geometry

Changes of the Resistivity

Measurement of strain, force, ..

Measurement of temperature, gas, ..

Principle: Resistance Changes

A

A

l

l

R

R


: Specific resistance

P. 1-10

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202010 1 T T aT T aR T R

C T R R 0at 00

131 109,3 K a

262 1058,0

K a

C T for

C T for K a

00

01018,4 3123

Example Platin-Resistance Thermometer

[IEC 751 / DIN EN 60751]

Class|T |= 0.39 K

-80°C – 120°C

Resistance Thermometer



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Negative Temperature Coefficient Resistance

A better conductor if heated

Temperature Coefficient

T

b

T

b

T T b

ee Re R R 00 0

11

0

b: Material Constant

R0: Resistance at the Temperature T0

T Carier Density

012 T

bdT dR

R

NTC: Negative Temperature Coefficient



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24d l R

d

l

: specific resistance

l

l Strain

l l

d d

Poisson Ratio

l

l

l l

d d

l l d

d

l

l

R

R

212

k

R

R 21 21k with

k R R 10

resistance:



Strain Gauges

P. 1-13

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Piezoresistive Effect

Strain Gauges (SG)

Higher Sensitivity

Small measurement Range

Metall SG Semiconductor SG

k R R 10 Dependence of the band structure of elasticlattice distortions due to the action ofexternal mechanical stresses.

Changes of

Geometry

Low Noise



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Strain Gauges (SG) – Metall-SG

• Piezoresistive Effect in Metall-SG

• Dependence of the piezoresistive effect Material

Nominar Resistance value without load

Poisson- Number

LoadChanges of Geometry

Changes of theElectric

Resistance



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• Example: higher Bandgap of InSb at higher pressure

(also other Semiconductors - 1000 MPa)

• Piezoresistive Effect in Semiconductors

LoadDeformation of

the crystallattice

Change of themobility of

charge career

Changes of resistivity

• Dependence of the piezoresistive Effect Orientation of the semiconductor cristall

Doping of the semiconductor

Type

Density

Distribution

Strain Gauges (SG) – Semiconductor-SG



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• Metall-SG

Wire-SG Wound Wire (d ≈ 20 µm)

Application by adhesive

Foil-SG

h ≈ 10 µm

Application by adhesive

Thin Film-SG

Application by sputtering or direct vapor deposition under

vakuum conditions (0,1 µm < h < 5 µm)

• Semiconductor-SG p- oder n-doped silicon (h ≈ 15 µm)

Application by adhesive or sputtering

Strain Gauges (SG) – Realization



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Strain Gauges (SG) – Examples



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nichtlineares Verhalten

Werkstoff Zusammensetzung k-Faktor

Konstantan 58% Cu, 42% Ni 2,04 bis

2,12

Nichrome V 80% Ni, 20% Cr 2,1 bis

2,63Nickel x% Ni -12 bis

20

Platin x% Pt 4,1

p-Si [111] 175

n-Si [100] -133

Strain Gauges (SG) – Materials



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Pressure Measurement Cell, Force Measurement

Sensors with Semiconductor strain gauges:



Strain Gauges

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Photo Resistance


Further Resistive Sensors


Anisotrope Magneto Resistive Effect (AMR)

Giant Magneto Resistive Effect (GMR)

Ni/Fe/Co

Ni/Fe/Co

Cu 5-10nmII

Without field

Higher Resistance

With magnetic field

Lower Resistance

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Resistive Sensors are mainly based on changes of resistvity or geometry

Are used for different Measurement quantites like:

- Temperature- Strain ( forces, pressure)

- Light

- Magnetic fields, position

Challenges are for example:

- Sensitivity- Measurement range

- Sensitive measurement procedures for small changes around a realitve

big nominal value

- Linearity should be investigated

- Wires may have an impact on the measurement value (small resistances,

temperature gradients along the wires)

- Contact resistances

What did we learn?

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Capacitive Sensors

Principle: Capacitance Changes

d

AC

r

0

Distance Changes

Changes of the Dielectric

Surface Changes

Changes in the Stray Field

Distance, Position, Material Thickness

e. g. Pressure Measurement

Distance, Position

e. g. Measurement of a Shift

Fill level, Humidity, Thickness of a Layer

e. g. Detection of Snow at an Airplane Wings

Detection of Conducting Material

e. g. Protection of Paintings in Museum

d

A

r



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Capacitance with Changes in Distance Capacitance with Changes

in Surface

Capacitance with Layered Dielectric

and Changes of Dip in DepthCapacitve Fill Level Sensor

for Isolating Liquids

P. 1-24

1 3 M t P i i l

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Capacitive Pressure Sensor:

Pressure

Application: Microphones



P. 1-25

1 3 M t P i i l

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Capacitive Sensors



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Capacitive sensors are able to measure changes of position, geometry and

material properties of the dielectric material

Examples for measurement quantities are:- Position

- Material thickness

- Moisture

- Fill level

- Pressure

For calculation of the haracteristic of the sensor, generally we should think about

parallel and series connection of part-capacitances.

Dependence on surface is linear, on distance is hyperbolic ( suitalbe only for

small distances)

Challenges:

- Stray field

- Unwanted changes of the geometry

- Sensitivity to conducting materials in the stray field, …

- Films can be built on the electrodes (Fill level Sensor)

- Moisture dependence

What did we learn?

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2

0

2

N A

µµR

N L r

m

Electro dynamic Measurement principles:

Magneto-elastic principle

N: Number of Windings

Rm: Magnetic Resistance

µ: Permeability

l , A: Length and cross section of the iron core

L: Inductance

Eddy current sensor

µAR m

Inductive Sensors



P. 1-28

Inductive Sensors1 3 Measurement Principles

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Elektrodynamische FühlerElectro dynamic principles


Inductive Sensors1.3 Measurement Principles

P. 1-29

Inductive Sensors1 3 Measurement Principles

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Inductive Sensors1.3 Measurement Principles

Eddy current principle

P. 1-30

Magnetic field of the inductance

Eddy currents in the target material

Eddy currents in the target material

Opposite magnetic field

Damping of the inductance

Measurements of:

- Material properties

- Material failures

- Distance (Proximity Sensor)

1 6 Classification of Sensors

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Aspects

- Signal

- System ability

- Signal parameters

Principle

- Resistive

- Capacitive

- Inductive

- Electro chemical

- …

Energy supply

- Active

- Passive

Development Level

- Elementary

- Integrated

- Intelligent

Application

- Automotive

- Environment

- Medicine

- Intelligent Home

- Research and Development

- …



1 4 S O t t Si l

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System ability Bus comunication

Output signalAnalogsignal

Binarysignal

Without buscommunication

Digitalsignal

Overfill sensorTemperatureExample:

Examples: CAN, LON, ASI, ..


1.4. Sensor Output Signals

P. 1-32

1 4 Sensor Output Signals

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Amplitudeanalog

Frequencyanalog

digital

Value

t

Timeanalog

Value

t

Value

t

Value

t

Signal value ~ Measurand Time ~ Measurand Frequency ~ Measurand Digital value ~ Measurand

t1 t2

f 2f 1

Static accuracy

Dynamic

Sensitivity to distortion

Signal processing

Static accuracyDynamicSensitivity to distortionSignal processing


1.4. Sensor Output Signals

P. 1-33


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Aspects

- Signal

- System ability

- Signal parameters

Principle

- Resistive

- Capacitive

- Inductive

- Electro chemical

- …

Energy supply

- Active

- Passive

Development Level

- Elementary

- Integrated

- Intelligent

Application

- Automotive

- Environment

- Medicine

- Intelligent Home


- …



1 5 P i S

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Passive Sensors

IDT

ReflectorsAntenna

RF request signal

RF response

Piezoelectric

crystal

Requestunit

Surface Acustic Wave -Sensors

Active Sensors

Piezo Electric Sensors

SensorEnergy Supply

Amplitude, Frequenz

Phase, Ankunftszeit



P. 1-35

1 5 Passive Sensors

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36

v T T K U

Seebeck effect

F 2

E F1 E F2

F 1

Metal 1 Metal 2

Vakuum-Niveau

E F

F 1

E F

F 2

Metal 1 Metal 2

Kontaktspannung U

Metal 2

UT

Measurement

Point

TV

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-200°C to +1000 °C

|T |= 0.25% -0,75 % of the measurement range limits

Example: Typ K (NiCr-Ni)

100K

mV 4,1)

100K

mV(-1,9 –

100K

mV 2,2K

Thermo electric voltage

should be amplified!

Examples for thermo couples



P. 1-37

1 5 Passive Sensors

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Piezo electric effect

Quarz Cristal

+

+

+

-

-

-Si

O

YF

YF

++++++++

+++

--------

---

-

-

-

+

+

+Si

O

x

yz



P. 1-38

1 5 Passive Sensors

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Piezo electric sensors

Acceleration sensors

S. 1-39Prof. Dr.-Ing. O. Kanoun


Prof. Dr.-Ing. O. Kanoun



P. 1-39


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Aspects

- Signal

- System ability

- Signal parameters

Principle

- Resistive

- Capacitive

- Inductive

- Electro chemical

- …

Energy supply

- Active

- Passive

Development Level

- Elementary

- Integrated

- Intelligent

Application

- Automotive

- Environment

- Medicine

- Intelligent Home


- …


S. 1-40Prof. Dr.-Ing. O. Kanoun

Chair for Measurement and Sensor Technology P. 1-40

1 6 Stages of Development of a Sensor System

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Signal

Measurement

Signal

Preprocessing

Signal

Processing

Elementar Sensor

Integrated Sensor

Intelligent Sensor

Prof. Dr.-Ing. O. Kanoun

1.6. Stages of Development of a Sensor System

Documents

1_Sensors