3441 industrial instruments 1 chapter 4 thermal sensors dr. bassam kahhaleh princess sumaya univ....
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34413441Industrial Instruments 1Industrial Instruments 1
Chapter 4Chapter 4
Thermal SensorsThermal Sensors
Dr. Bassam KahhalehDr. Bassam Kahhaleh
Princess Sumaya Univ.Princess Sumaya Univ.Electronic Engineering Dept.Electronic Engineering Dept.
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Thermal SensorsThermal Sensors
ObjectiveObjective
Understand how thermal sensors work and Understand how thermal sensors work and how to interface them.how to interface them.
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Thermal SensorsThermal Sensors
Metal ResistanceMetal Resistance
Energy bands for solids:Energy bands for solids:Energy gap: required energy for the electron to become freeEnergy gap: required energy for the electron to become free
Metals
W
Valence
Conduction
Semiconductors
W
Valence
Conduction
Insulators
W
Valence
Conduction
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Thermal SensorsThermal Sensors
Metal ResistanceMetal Resistance
−100 0 100 200 300 400 500 600
Temperature (°C)
R(T
)R
(25°
C)
1
2
3
NickelPlatinum
A
lR
)25(
)(
)25(
)(
T
R
TR
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Thermal SensorsThermal Sensors
Metal ResistanceMetal ResistanceLinear ApproximationLinear Approximation
Quadratic ApproximationQuadratic Approximation
]1[)()( 00 TTRTR
12
12
00 )(
1
TT
RR
TR
T1 T2T
R1
R2
])(1[)()( 2210 TTTRTR
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Thermal SensorsThermal Sensors
Resistance-Temperature Detectors (RTD)Resistance-Temperature Detectors (RTD) SensitivitySensitivity
0: 0.004/°C ~ 0.005 /°C
Response TimeResponse Time0.5 ~ 5 seconds
ConstructionConstructionWire
Signal ConditioningSignal ConditioningBridge with lead compensation
Dissipation Constant (Self-heating)Dissipation Constant (Self-heating)DP
PT
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Thermal SensorsThermal Sensors
RTDRTDExample
0= 0.005/°C
R = 500 Ω at 20°C
PD = 30 mW /°C
R1 = R2 = 500 Ω
VS = 10 V
RTD is at 0°C
Find R3
R 1 R 2
R 3
VSD
RTD
a b
c
450)]200(005.01[500)(TR
CT
WP
AI
8.1030.0
054.0
054.0450*)011.0(
011.0450500
10
2
5.454)]208.1(005.01[5003R
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Thermal SensorsThermal Sensors
ThermistorsThermistors
−20 0 20 40 60 80 100
Temperature (°C)
Res
ista
nce
(K
Ω)
10
20
30
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Thermal SensorsThermal Sensors
ThermistorsThermistors SensitivitySensitivity
~ 10% /°C
Response TimeResponse Time0.5 ~ 10 seconds
ConstructionConstructionDiscs, beads, rods … etc
Signal ConditioningSignal ConditioningDivider circuit, Bridge
Dissipation Constant (Self-heating)Dissipation Constant (Self-heating)
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Thermal SensorsThermal Sensors
ThermistorsThermistorsExample
R = 3.5 KΩ at 20°C
S = - 10% /°C
PD = 5 mW /°C
VO = 5 at 20°C
Self-heating error?
KR 50.31
CT
mWK
P
42.15
1.7
1.75.3
)5( 2
KC
KCKRTH 3
5.3*%1042.15.3
R 1
R TH
10 V
V D
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Thermal SensorsThermal Sensors
ThermocouplesThermocouples
T2 T1
Seebeck Effect
T2T1EMFHeat Flow
I
Peltier Effect
)( 12 TTE
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Thermal SensorsThermal Sensors
ThermocouplesThermocouples
TM
TR
TR
+
VTC
−
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Thermal SensorsThermal Sensors
ThermocouplesThermocouples
TypeType MaterialMaterial Normal RangeNormal Range
J Iron-constantan -190°C to 760°C
T Copper-constantan -200°C to 371°C
K Chromel-alumel -190°C to 1260°C
E Chromel-constantan -100°C to 1260°C
S 90%platinum, 10%rhodium-platinum 0°C to 1482°C
R 87%platimum, 13%rhodium-platinum 0°C to 1482°C
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Thermal SensorsThermal Sensors
ThermocouplesThermocouples
−200 0 200 400 600 800 1000 1200
Temperature (°C)
VT
C (
mV
)
10
30
50
Type E
Type J
Type R
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Thermal SensorsThermal Sensors
ThermocouplesThermocouples
−20 0 20 40 60 80 Temperature (°C)
VT
C (
mV
)
1
2
4 0 °C Ref.
3 20 °C Ref.
0
−1
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Thermal SensorsThermal Sensors
ThermocouplesThermocouples SensitivitySensitivity
Type J: 0.05mV /°C
Type R: 0.006mV /°C
Response TimeResponse Time0.01 ~ 20 seconds
ConstructionConstructionWelded junction
Signal ConditioningSignal ConditioningHigh-gain differential amplifier, with high CMRR
Reference Compensation (cold junction comp.)Reference Compensation (cold junction comp.)
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VC
Thermal SensorsThermal Sensors
ThermocouplesThermocouples Cold junction Compensation Cold junction Compensation
K +
TemperatureSensor
SignalConditioning
T
TrefVout
KVTC
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Thermal SensorsThermal Sensors
Bimetal StripsBimetal Strips Thermal ExpansionThermal Expansion
Tll 10
γ1
γ2 < γ1
T0
T > T0
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Thermal SensorsThermal Sensors
Gas ThermometersGas ThermometersConstant Volume:Constant Volume:
Liquid-Expansion ThermometersLiquid-Expansion Thermometers
2
2
1
1
T
p
T
p
TTVTV 1)()( 0
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Thermal SensorsThermal Sensors
Solid-State Temperature SensorsSolid-State Temperature Sensors~ 12 mV / K~ 12 mV / K
PD = 5 mW / °C
At 293 K:
VT = 3.516 V
I = (5 – 3.516) / 510 = 0.0029 A
P = 3.516 * 0.0029 = 10.2 mW
ΔT = 10.2 / 5 = 2.04 °C
Increase R
510 Ω
T
5 V
V T
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Thermal SensorsThermal Sensors
Solid-State Temperature SensorsSolid-State Temperature SensorsExample
J-type TC: ~ 50 μV / °C
SS sensor: 8 mV / °C
VO = 2 V @ 200 °C
VTC (200°C) = 10.78 mV
TC Gain = 8 mV / 50 μV
= 160 Total Gain = 2000 / 10.78
= 185.5
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Thermal SensorsThermal Sensors
Solid-State Temperature SensorsSolid-State Temperature SensorsExample
V out
11.59 K
−
+
10 K
11.59 K
10 K
320 K
−
+
2 K
320 K
2 K
T
Tref
SS
−8 mV / °C
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Thermal SensorsThermal SensorsExample
Turn-on alarm when T = 10 ± 0.5 °C
Turn-off alarm when T ≤ 8 °C
RTH = 10 KΩ @ 10 °C
= 11 KΩ @ 8 °C
Keep self-heating within ± 0.5 °C. Use ± 0.25 °C P = (5 mW / °C)*(0.25 °C) = 1.25 mW @ 10 °C, ITH = 0.354 mA, VTH = 3.5 V
Using voltage divider with 5 V supply: R = (5 – 3.5) / 0.354 = 4.28 KΩ @ 10 °C, VD = 1.5 V
@ 8 °C, VD = 1.41 V Hysteresis = 0.09 V
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Thermal SensorsThermal SensorsExample
+
−
9 K
500 K
Vref = 1.5 V
Vout
R TH
4.28 K
5 V
V D
2.327 K
1 K
5 V
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Thermal SensorsThermal SensorsExample
Measured T = 50 °C ~ 80 °C (error ≤ ± 1 °C)
VO = 0 ~ 2 V
RTD: R(65°C) = 150 Ω
(65°C) = 0.004 / °C
PD = 30 mW / °C
R(50°C) = 150 [ 1 + 0.004 (50 – 65) ] = 141 Ω R(80°C) = 150 [ 1 + 0.004 (80 – 65) ] = 159 Ω Keep self-heating within ± 1 °C P = (30 mW / °C)*(1 °C) = 30 mW @ 80 °C, IRTD = 13.7 mA, VRTD = 2.17 V
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Thermal SensorsThermal SensorsExample
10 K
−
+
10 K
10 K
10 K
220 220
141 RTD
5 V
V out
10 K
+
−
138 K
@ 50 °C: RRTD = 141 Ω, ΔV = 0, Vout = 0
@ 80 °C: RRTD = 159 Ω, ΔV = 0.1447 V, Vout = 0.1447 * 13.8 = 2 V
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Thermal SensorsThermal SensorsExample
Measured T = 500 ~ 600 °F (260 °C ~ 315.6 °C)
VO = 0 ~ 5 V
J-type TC: Tref = 25 °C
VTC(260 °C) = 12.84 mV
VTC(315.6 °C) = 15.9 mV
Vout = m VTC + V0
0 = m(0.01284) + V0
5 = m(0.01590) + V0
m = 1634, V0 = − 21, Use Gain = 100 * 16.34
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Thermal SensorsThermal SensorsExample
V out
−
+
10 K
163.4 K
10 K
100 K
−
+
1 K
100 K
1 K
T
Tref = 25 °C
2.88 K
1 K
5 V
Vref = 1.289 V