2. Sensor Properties 2.0 Introduction 2.1 Static Properties · 2. Sensor Properties ... 2.0...
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P. 2-1 2. Sensor Properties 2.2 Dynamic Properties 2.1 Static Properties Sensitivity (Empfindlichkeit), Sensitivity to influence effects (Empfindlichkeit auf Einflussgrößen), Resolution (Auflösung), Reproducibility (Reproduzierbarkeit), Linearity (Linearität), Hysteresis (Hysterese), Drift, Errors(Ausfall) 2.0 Introduction Prof. Dr.-Ing. O. Kanoun Chair for Measurement and Sensor Technology Dead time (Totzeit) Slow rate (Anstiegszeit) Delay Time (Verschiebungszeit) Settling Time (Einschwingzeit)
Transcript of 2. Sensor Properties 2.0 Introduction 2.1 Static Properties · 2. Sensor Properties ... 2.0...
P. 2-1
2. Sensor Properties
2.2 Dynamic Properties
2.1 Static PropertiesSensitivity (Empfindlichkeit), Sensitivity to influence effects (Empfindlichkeit auf Einflussgrößen), Resolution (Auflösung), Reproducibility (Reproduzierbarkeit), Linearity (Linearität), Hysteresis (Hysterese), Drift, Errors(Ausfall)
2.0 Introduction
Prof. Dr.-Ing. O. KanounChair for Measurement and Sensor Technology
Dead time (Totzeit)Slow rate (Anstiegszeit)Delay Time (Verschiebungszeit)Settling Time (Einschwingzeit)
P. 2-2
Application Sensor
Which criterions are important?
Sensor?
Special Requirements
PrincipeTypPackaging….
2.0 Introduction
Prof. Dr.-Ing. O. KanounChair for Measurement and Sensor Technology
P. 2-3
Preselection of sensors
Typical values
Application conditions: Temperature, Polluants, contactingEfficiency, long time stability, .....
Sensor SchnittstelleSignalauswertung
TGeometrical dimensions, integrability
2.0 Introduction
P. 2-4
Resistance Thermometer
P. 2-5
Example of a Data Sheet of a Resistance Thermometer Pt 100
P. 2-6
Beispiel: Datenblatt eines Widerstandsthermometers (Pt100)
P. 2-7
Capacitive fill level sensor
S. 2-8
Capacitive fill level sensor
Prof. Dr.-Ing. O. KanounChair for Measurement and Sensor Technology
P. 2-9
Resolution
Sensitivity
Precision
Drift
Reproducibility
Sensitivity on influence factors
HysteresisLinearity
Failure
2.1 Static Properties
Prof. Dr.-Ing. O. KanounChair for Measurement and Sensor Technology
Messgröße
SensorAusgangs-signal
empfindlich
Sättigung
P. 2-10
Changes of the signal versus changes of the input
MeasQXE a
Sensitivity
A high sensitivity is important!
aX
2.1 Static Properties
Prof. Dr.-Ing. O. KanounChair for Measurement and Sensor Technology
Sensitive
Saturation
Measured Quantity
Output Signal
P. 2-11
T in °C-50 0 50 100 150 200
R in
0
200x103
400x103
600x103
800x103
1x106
T in °C-50 0 50 100 150 200
dR/d
t in
-60000
-50000
-40000
-30000
-20000
-10000
0
Tb
Tb
TTb
eeReRR 000
11
0
b: Material Constant
R0: Resistance at the Temperature T0R
Tb
TbeeR
dTdRE
Tb
Tb
2200
better sensititvity
Sensitivity: Example NTC-Resistance
2.1 Static Properties
Prof. Dr.-Ing. O. KanounChair for Measurement and Sensor Technology
P. 2-12
Sensitivity and Accuracy
For a more sensistive sensor an observed change of the sensor signal ycorresponds to a smaller change x of the measured quantity
Messgröße x
Ausgangssignal y
y
x1 x2
Sensor1
Sensor2
A measurement deviation at the output signal leads to a smaler deviation of the measurement quantity
2.1 Static Properties
Prof. Dr.-Ing. O. KanounChair for Measurement and Sensor Technology
Output Signal y
Measured Quantity x
P. 2-13
Messgröße
Sensorsignal
T: Einflussgröße
e. g. Influence of temperature on
Sensor signal changes depending on variable which different to the measurement quantity
- Changes of material properties
- Changes of activation energies
- Changes of transport mechanisms (Diffusion)
Cross Sensitivity
e. g.: A gas sensor for oxygen shows sensitivity to other gases
Sensitivity on modifying input
Sensitivity to Interfering inputs
Sensitivity to Influence Factors
2.1 Static Properties
Prof. Dr.-Ing. O. KanounChair for Measurement and Sensor Technology
Sensor Signal
Measured Quantity
T: Influence Factor
Sensor reacts on the same way on the measurand and the interfering inputs
P. 2-14
..smallest change of the input signal leading to an observable change of the output signal
Example: PotentiometerSensor signal changes is steps
Typical Description xx Measurand
Example: Resolution of a Person Scales: 100 g
xx % of the upper range value
Resolution
2.1 Static Properties
Prof. Dr.-Ing. O. KanounChair for Measurement and Sensor Technology
P. 2-15
LSB: Least Significant Bit
11001001
n=8 Bit
nLSBUUU
2minmax
Umin ≡ 00000001Umax ≡ 11111111
Example:A/D-converters of 8 Bit resolution
Resolution of Analog/Digital-Converters
2.1 Static Properties
Prof. Dr.-Ing. O. KanounChair for Measurement and Sensor Technology
P. 2-16
Reproducibility /Repeatability
Possible Causes:
• Thermal Noise
• Material elasticity
• Contamination of Bio and Gas Sensors
Sensor system delivers not the same value, even if the measurement conditions remain the same
Typical description:
MBEymax
Measurand
MBE: end value of the measurement range
maxy : Maximal deviation of the output signal
2.1 Static Properties
Prof. Dr.-Ing. O. KanounChair for Measurement and Sensor Technology
P. 2-17
Linearity
The transfer behaviour of a system is not linear
Cause: measurement principle
typical description:
maxy
MBEymax
Examination by linearization or numerical differenciation
2.1 Static Properties
Prof. Dr.-Ing. O. KanounChair for Measurement and Sensor Technology
P. 2-18
Example: Linearity Deviation of an NTC-Resistance
T in °C-50 0 50 100 150 200
R in
-400x103
-200x103
0
200x103
400x103
600x103
800x103
1x106
y= 127811 - 2233 x
Tb
Tb
TTb
eeReRR 000
11
0
T in °C-50 0 50 100 150 200
R/R
max
in %
-20
0
20
40
60
80
100
2.1 Static Properties
Prof. Dr.-Ing. O. KanounChair for Measurement and Sensor Technology
P. 2-19
Hysteresis
Causes
• Hysteresis of Materials like ferromagnetics
• Friction and settlement of multipart (Screwed or clamped) messurement setups
• Plastic deformation of the assmbly between chip and packaging
Sensor output signal is dependent on previous values of the input
typ. Angabe:
MBEymax
Sensor signal is dependent of the history The dependence of the output signal from
input signal is not unique!
2.1 Static Properties
P. 2-20
Aging/Drift
Causes, e. g. :- of Materials
Properties of the sensor system change with time.
Drift: is a special type of aging describing:slow changes with time
- Setting of atoms in the cristal grid Time
Out
put S
igna
l
Linear Sensors: Drift of the zero point Drift of sensitivity
Tolerance Band
calibration!
Ageing is dependent on the application conditions
2.1 Static Properties
Prof. Dr.-Ing. O. KanounChair for Measurement and Sensor Technology
P. 2-21
Failure
MTBF (Mean Time between Failures)
Availability of a sensor system
MTTR (Mean Time to Repair)
[DIN EN/IEC61709]MTTRMTBF
MTBFV
2.1 Static Properties
Prof. Dr.-Ing. O. KanounChair for Measurement and Sensor Technology
Impulse
Characterization of dynamic behaviour
x(t)=x0sin(t) H0(
Frequency excitation
Step-Function
(AmplitudePhase
y(t)=y0sin(t+)
Prof. Dr.-Ing. O. KanounProfessur für Mess- und Sensortechnik S. 1-22
Linear system
Linear system
Linear system
2.2 Dynamic Properties
P. 2-23
tL: Dead time (Totzeit)tA: Slow rate, rise time (Anstiegszeit)tV: Delay time (Verschiebungszeit)tE: Settling time (Einschwingzeit)
2.2 Dynamic PropertiesStep Response of a Sensor System (general case!)
Prof. Dr.-Ing. O. KanounChair for Measurement and Sensor Technology
F(P) 1/F(P)xe(t) xa(t) xo(t)= xa(t) * g(t)
sensor Correction ofdynamic
behaviour
)(*)()()(0
tgtxdtxtx a
t
ao
)(/1)( 1 PFLtg Transferfunktion:
Dynamic Correction of Linear Systems
Prof. Dr.-Ing. O. KanounProfessur für Mess- und Sensortechnik
S. 1-24
see chapter applications of amplification circuits
2.2 Dynamic Properties
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