Technical Research Sensor Technology ECE 2799 D04 Example Design – Milestone 1
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Technical Research Sensor Technology
ECE 2799 D04
Example Design – Milestone 1
Measurement System
AcousticBiologicalChemicalElectricalMagneticMechanicalOpticalRadiantThermal
LCDLEDs7-segmentdot-matrixalarmetc…
InputSensor
ModifierOutput
Transducer
Power Supply
Sensor SelectionExample Design: Beer Keg Tap Temperature Sensor
Environmental Conditions Input/Output Range Linearity Offset Operating Life Output Format Overload Characteristics Repeatability/Hysteresis Resolution/Accuracy Sensitivity/Selectivity Size/Cost/Weight Speed of Response Stability (long and short term)
specificgeneral
5 - 7 0C (4 - 8 0C) < 1degree accuracy waterproof durable inexpensive fast low power
<50C 5-70C >70C
Types of temperature sensors
ThermoresistiveRTD (resistive temperature detector) thermistor (thermometer + resistor)
Thermoelectricthermocouple
Semiconductor (IC’s)pn diodebipolar junction transistor
Opticalphosphorescent signal
Acousticpiezoelectric
Thermoresistive sensors
advantages: • temperature range• simplicity of interface circuits• sensitivity• long term stability• inexpensive
disadvantages•not rugged•self-heating
RTD (PTC)
advantages • temperature range• sensitivity• inexpensive
disadvantages: • PTC less sensitive• nonlinear • self-heating
NTC/PTC Thermistor
Thermoelectric sensor
thermocouples
advantages:•temperature range•very ruggedness•inexpensive•fast depending on size
disadvantages:•error is larger than RTD or IC sensor•some types are very sensitive to moister
Semiconductor IC sensors
advantages:•temperature range•highly linear•small•accurate•easy to interface
disadvantages:•sensitive to shock
)2/exp(0 TkqVII B
Optical temperature sensors
Richard Boxfluorescent tubes under high tension wires outside of Bristol England
advantages:•thermally stable•waterproof•good in hostile environments
disadvantages:•expensive•impractical (too big, complicated, etc.)
Acoustic Temperature sensorsadvantages:•thermally stable•waterproof•good in hostile environments
disadvantages:•expensive•complicated circuitry
T
dry air
ultrasound
)/(15.273
5.331 smT
Sensor comparisonsThermoresistors Semiconductor
Temperature IC
RTD Thermistor (NTC)
Analog/Digital
temperature good range good range good range
cost high cost lower cost inexpensive
accuracy most precise accurate very accurate
durability sensitive to strain and shock
rugged sensitive to shock
response time slow fast fast
power problems with self-heating
lower power low power
NTC Thermistor
00
11exp
TTRR TT
Negative Temperature Coefficient
material constant
zero-power resistance at temp T
example
Types of NTC Thermistors
Metallized surface contact slow response times high power dissipations
low cost Bead type fast response times
high stability/reliabilitylow power dissipationmore costly
• bare beads no environmental protection.• glass coated beads not rugged• glass probes easy to handle, durable, stable• glass rods good for mounting on circuit boards
www.thermometrics.com
Selecting a NTC thermistor: glass probe
NTC Thermistor: response time
thermal time constant:
/1 t
as eP
TT
initial ambient temperature
electric power
dissipation constant
Ta=25 0C
P= 0.020 Watts
=0.70 mW/0C
t = 18 – 23 msec
=18 msec
NTC Thermistor: Sensitivity
T (0C) RT/R0
4 2.078
5 2.004
6 1.930
7 1.856
8 1.787
T
R
RT
T
1Temp
Coeff
=-3.7 %/C @ 5 C
NTC Thermistor: Sensitivity
T (0C) RT/R0 RT/R0 min RT/R0 max
4 2.078 2.070 2.112
5 2.004 1.994 2.034
6 1.930 1.920 1.959
7 1.856 1.851 1.888
8 1.787 1.784 1.820
00
11exp)1(
TTXRR TT
X=1%
X=5%
resistor tolerance
RT=(RT/RT0)RT0+/- 0.02RT0
Sensor comparisonsThermoresistors Semiconductor
Temperature IC
RTD Thermistor (NTC) Analog
temperature good range good range
(-80 to 160 0C)
good range
cost high cost lower cost inexpensive
accuracy most precise accurate
(+/- 0.02RT0)
very accurate
durability sensitive to strain and shock
rugged sensitive to shock
response time slow fast
(18-23 msec)
fast
power problems with self-heating
lower power
(max 0.02 W)
low power
Other R=1k-1M
Sensor Classification
what does it measure? what are its specifications? what physical phenomenon is it sensitive to? what material is it fabricated from? what conversion measurement does it use? what are its field of application?
what does it measure (stimulus)?
Acoustic Biological Chemical Electrical Magnetic Mechanical (pressure) Optical Radiant Thermal
Wave amplitude, phase, polarizationSpectrumWave velocityOther
Wave amplitude, phase, polarizationSpectrumWave velocityRefraction indexReflectivity, absorptionOther
MagnitudeDifferenceRate of changeOther
what are its specifications?
Environmental Conditions Cost Input/Output Range Linearity Offset Operating Life Output Format Overload Characteristics Repeatability/Hysteresis Resolution/Accuracy Sensitivity/Selectivity Size/Weight Speed of Response Stability (long and short term)
what are its specifications?
Environmental Conditions Cost Input/Output Range Linearity Offset Operating Life Output Format Overload Characteristics Repeatability/Hysteresis Resolution/Accuracy Sensitivity/Selectivity Size/Weight Speed of Response Stability (long and short term)
temperatureaccelerationvibrationshockambient pressuremoisturecorrosive materialselectromagnetic fields
what are its specifications?
Environmental Conditions Cost Input/Output Range Linearity Offset Operating Life Output Format Overload Characteristics Repeatability/Hysteresis Resolution/Accuracy Sensitivity/Selectivity Size/Weight Speed of Response Stability (long and short term)
what physical phenomenon is it sensitive to?
Biological Chemical Electric, Magnetic or EM wave Heat Mechanical displacement or wave Radioactivity, radiation Other
what conversion measurement does it use?
Thermoelectric Photoelectric Photomagnetic Thermoelastic Electroelastic Piezoelectric Other
What are its field of application?
Agriculture Civil Engineering Energy, Power Health, Medicine Manufacturing Military Scientific Measurements Transportation, automotive Recreation, toys Space Other
Temperature Scaletemperature scales1664 Hooke: zero scale at freezing point of distilled water (zero point)1694 Renaldi: 2 points linear (melting point ice and boiling point water) divide by 12 1701 netwon: 2 points linear (zero point and armpit temperature of healthy englishman (point 12) water boils: point 341706 Fahrenheit: zero point mixture of water, ice, salt…..96 degrees (found in the blood of a healthy man)…ice melts 32, boils 212degrees1742 celsius: ice melts 0 and water boils at 100
kelvin…..triple point…at 273.16degree kelvin, at 4.58 mm Hg pressue..water vapor, liquid and ice can coexist. (approximately 0 degrees C)….linear, zero point is temp where kinetic energy of all moving particle is zero….absolute zero…not possilbe!
Sensor
Advantages of electrical measurement systems
many microelectronic circuits already exist (applications: amplification, filtering, modulation)
many options for information display or recording electrical signal is well suited for transmission
Sensor
AcousticChemicalElectricalMagneticMechanicalOpticalRadiantThermal
Electrical
Temperature Measurement
sensor type:contact sensor or thermal radiation sensor?
conduction, convection, radiation
Contact Temperature Sensorcontact sensing….measurement is complete when no more thermal gradient between surface (beer) and sensor probe.
dQ=aA(T1-T) dt Q=absorbed heat,a=thermal conductivity of sensor-beer interfaceA=heat transmitting surface areaT=temperature
sensor, specific heat c and mass m
dQ=mcdT
aA(T1-T) dt=mcdT
T=T1-Ke-t/tT thermal time constant
measurement after 5 -10 time constants
tT=mc/a/A
(short time constant)
sensing element
1.sensing element: low specific heat, high thermal conductivity, strong and predictable temp sensitivity.2.contacts: interface between sensing element and electrical circuit….low thermal conductivity, low electrical resistance (sometimes used to support sensor)3. protective element: physically protects sening element from environment: low thermal resistance, high elctrical isolation properties……impermeable to moisture or other factes that spuriously affect sensing element
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