Post on 14-Apr-2018
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Task
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It is time to turn up the heat but firstyou must learn how to measure it
Temperature Sensor
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Relative Scales
Fahrenheit (F) Celsius (C)
Absolute Scales
Rankine (R) Kelvin (K)
Temperature Measurement Scales
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100:C373:K
273:K
255:K
0:C
-18:C
-273:C 0:K-460:F 0:R
0:F
32:F
460:R
492:R
672:R212:FFahrenheit
[F] = [C] 9/5 + 32
Celsius[C] = ([F] 32) 5/9
Kelvin
[K] = [C] + 273.15
Rankine
[R] = [F] + 459.67
Imperial
Fahrenheit (F) / Rankine (R)
+/- 460
Metric
Celsius (C) / Kelvin (K)
+/- 273
Temperature Measurement Scales
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(F) = 9/5*(C) +32
(C) = 5/9*[(F)
32]
(F) = (R) 459.67
(C) = (K) 273.15
Relationship of Temperature Measurement Scales
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Methods of Temperature Measurement
1. Mechanical Methods
2. Electrical Methods
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Methods of Temperature Measurement
1. Thermocouples
2. Thermistors
3. Electrical resistance change (RTD)
4. Pyrometers
5. Expansion of materials
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Seebeck Effect:
The generation of
current in a circuit
comprising of two wires
of dissimilar metals in
the presence of
temperature difference
Thermocouples
When 2 dissimilar metals are joined together toform a junction, an emf is produced which is
proportional to the temperature being sensed.
The magnitude of emf depends on the junctiontemperature.
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Typical Industrial Thermocouple Assembly
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TCs are identified by a single letter type and
grouped according to their temperature range Base Metals up to 1000 C
Type J, Type E, Type T, Type K
Noble Metals up to 2000 C
Type R, Type S, Type B
Refractory Metals up to 2600 C
Type C, Type D, Type G
Thermocouple Types
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TC
Type
Colours Range C Positive Lead
(Coloured)
Negative Lead
(all Red)
J White/Red -210 to 1200 Iron Constantan
E Purple/Red -270 to1000 Chromel Constantan
T Blue/Red 0 to 400 Copper Constantan
K Yellow/Red -270 to1372 Chromel Alumel
R Black/Red -50 to 1768 Platinum-13%
rhodium
Platinum
S Black/Red -50 to 1768 Platinum-10%
rhodium
Platinum
B Grey/Red 0 to 1700 Platinum-30%
rhodium
Platinum-6% rhodium
C White-Red/Red
0 to 2320 Tungsten/5%rhenium
Tungsten 26% rhenium
Chromel = Nickel-chromiumAlumel = Nickel-aluminumConstantan = Copper-nickel
Metal Combinations
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Type T Thermocouple (Blue & Red) Reference Junction 0 C
C 0 1 2 3 4 5 6 7 8 9
0 0.000 0.039 0.078 0.117 0.156 0.195 0.234 0.273 0.312 0.352
10 0.391 0.431 0.470 0.510 0.549 0.589 0.629 0.669 0.709 0.749
20 0.790 0.830 0.870 0.911 0.951 0.992 1.033 1.074 1.114 1.155
30 1.196 1.238 1.279 1.320 1.362 1.403 1.445 1.486 1.528 1.570
40 1.612 1.654 1.696 1.738 1.780 1.823 1.865 1.908 1.950 1.993
Thermocouple Tables
Voltage to Temperature Conversion
1.445 mV equal to temperature ..
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Thermocouple Callibration Charts
Voltage to Temperature Conversion
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Thermistor, a word formed by combining thermal with
resistor, is a temperature-sensitive resistor fabricatedfrom semiconducting materials.
The resistance of thermistors decreases proportionally
with increases in temperature.
The operating range can be -200C to + 1000C
Thermistors
Th i t
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Thermistors
The thermistors can be in the shape of a rod,bead or disc.
Manufactured from oxides of nickel, manganese,iron, cobalt, magnesium, titanium and othermetals.
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erm s ors
The word that best describes the thermistors issensitive
Th i t Ch t
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Thermistor Charts
Resistance to Temperature Conversion
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Advantages:
Small sizes and fast response
Low cost
Suitability for narrow spans
Disadvantages:
More susceptible to permanent decalibration at high
temperatures.
Use is limited to a few hundred degrees Celsius. Respond quickly to temperature changes, thus,
especially susceptible to self-heating errors.
Very fragile
erm s ors
El t i l R i t Ch (RTD)
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Electrical Resistance Change (RTD)
Resistance Temperature
Detector- RTD RTD (Resistance Temperature Detector) is a temperature
sensitive resistor.
It is a positive temperature coefficient device, which means
that the resistance increases with temperature.
The resistive property of the metal is called its resistivity.The industry standard is the platinum wire RTD(Pt100) whose base resistance is exactly 100.00
ohms at 0.0 C.
El t i l R i t Ch (RTD)
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Electrical Resistance Change (RTD)
Platinum Wire RTDs (PRTs)
PRTs have established themselves as the de-facto industrystandard for temperature measurement, and for many reasons:
linear temperature sensors
Resistance vs temperaturecharacteristics are stable andreproducible
linear positive temperaturecoefficient (-200 to 800 C)
very accurate and suitable for use asa secondary standard
Electrical Resistance Change (RTD)
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Electrical Resistance Change (RTD)
Platinum Scale ( 0 to 100 C )
Electrical Resistance Change (RTD)
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Electrical Resistance Change (RTD)
International Practical scale for Temperature
(0 to 650. 30 C)
Electrical Resistance Change (RTD)
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Electrical Resistance Change (RTD)
International Practical scale for Temperature
(Below 0 C)
Electrical Resistance Change (RTD)
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Electrical Resistance Change (RTD)
International Practical scale for Temperature
Electrical Resistance Change (RTD)
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Other RTDs
10 ohms CopperRTD - .00427 coefficients
100 ohms Platinum RTD - .00385 coefficients
(new IEC)
100 ohms Platinum RTD - .00392 coefficients (old)
120 ohms Nickel RTD - .00672 coefficient
604 ohms Nickel-Iron RTD - .00518 coefficientsAll base resistances are specified at a temperature of 0 degrees C
A Pt1000 will have a base resistance of 1000 ohms at 0 deg. C
Electrical Resistance Change (RTD)
RTDs with a bridge circuit
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Only practical if the RTD lead wires are short.
In many applications the RTD is located far from the conditioning
circuit adding extra resistance because the length of the copperlead wire.
Cu = 0.0302 per ft.
How much error will 100 ft length of Cu lead wire introduce?
RTDs with a bridge circuit
Most RTDs have an extra
wire to compensate for
the length of lead wire.
RTD Colour Code
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Not standardized but this is common colourarrangement. Some (like in the lab) will useBLK-BLK-RED
RTD Colour Code
Pyrometer
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Pyrometry is a technique for measuring temperature
without physical contact
An apparatus for measuring high temperatures that usesthe radiation emitted by a hot body as a basis for
measurement.
Radiation pyrometers ( measurement of radiant energy)
Pyrometer
Radiation Pyrometer
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Radiation pyrometers
Radiation Pyrometer
Radiation Pyrometer
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Optical pyrometers (600 to 3000 C)
Radiation Pyrometer
basic principle of using the human eye to match the brightness
of the hot object to the brightness of a calibrated lamp
filament inside the instrument
Compare incident radiation to internal filament radiation
Expansion Thermometers
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Bimetallic Thermometer
(Expansion of solids)
Expansion Thermometers
Effect of unequal expansion of a bimetallic strip
Bimetallic thermometer
-Different metals have difference coefficient.
-Configured as spiral or helix for compactness
- Can be used with a pointer to make aninexpensive compact rugged thermometer.
Expansion Thermometers
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Bimetallic Thermometer
(Expansion of solids)
Expansion Thermometers
Expansion Thermometers
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Bimetallic Thermometer
(Expansion of solids)
Thermal expansion methods: Bimetallic sensors
Expansion Thermometers
Expansion Thermometers
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Filled Thermal Systems(Filled System Thermometer, Filled Bulb Thermometer)
Expansion Thermometers
Similar operation as the liquid in glass
Bulb
Capillary tube
Pressure element Scale
Spiral TypeBourdon Tube
Expansion Thermometers
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Filled Thermal System Classes(Filled System Thermometer, Filled Bulb Thermometer)
Expansion Thermometers
Class l A,B Liquid filled
Class ll A,B,C,D Vapour filled
Class lll A,B Gas filled
Class V A,B Mercury Filled
Expansion Thermometers
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Filled Thermal System Classes(Filled System Thermometer, Filled Bulb Thermometer)
Expansion Thermometers
Temperature Range Response
Class l: -125 F to + 600 F Slowest
Class ll: -40 to 32 or 32 to 600 F Fastest
Class lll: -450 F to +1400 F Fast
Class V: -40 F to +1200 F Fast
Data Required to Provide Measurement of Process
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Data Required to Provide Measurement of ProcessTemperature
Data Required to Provide Measurement of Process
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qTemperature
Data Required to Provide Measurement of Process
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qTemperature
Data Required to Provide Measurement of Process
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qTemperature
Criteria for Selecting a Suitable Temperature Measuring
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g p gInstrument
Summary of Temperature Sensor Characteristics
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y p
Summary of Temperature Sensor Characteristics
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