PowerPoint-Pr

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Industrial Instrumentation
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Temperature Sensor

• It is time to turn up the heat but first you
  must learn how to measure it

PEC UET Lahore Dr. Shahid
Naveed
25. Mai 2016 / Dr. Ing
Naveed Ramzan 2
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Temperature Measurement Scales

• Relative Scales
• Fahrenheit (F)
• Celsius (C)
• Absolute Scales
• Rankine (R)
• Kelvin (K)

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Temperature Measurement Scales
Imperial Fahrenheit (F) / Rankine
(R) /- 460
Metric
Celsius (C) / Kelvin
(K) /- 273
Fahrenheit F C 9/5 32 Celsius C
(F - 32) 5/9 Kelvin K C
273.15 Rankine R F 459.67  
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Relationship of Temperature Measurement Scales

• (F) 9/5(C) 32
• (C) 5/9(F) 32
• (F) (R) 459.67
• (C) (K) 273.15

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Methods of Temperature Measurement

• Mechanical Methods
• Electrical Methods

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Methods of Temperature Measurement

1. Expansion thermometers
2. Filled system thermometers
3. Electrical temperature instruments
4. Pyrometers

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Methods of Temperature Measurement

1. Expansion thermometers
2. Filled system thermometers
3. Electrical temperature instruments
4. Pyrometers

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Expansion thermometers

• Expansion of solids
• Bimetallic thermometers
• Expansion of liquids
• Liquid in glass thermometers
• Liquid in metal thermometers
• Expansion of liquids
• Gas thermometers

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Expansion thermometers

• Bimetallic Thermometer
• (Expansion of solids)

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Expansion Thermometers

• Bimetallic Thermometer
• (Expansion of solids)

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Thermal expansion methods Bimetallic sensors
Expansion Thermometers

• Bimetallic Thermometer
• (Expansion of solids)

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Expansion Thermometers

• Liquid in glass Thermometer
• (Expansion of liquids)

• Liquid in metal Thermometer
• (Expansion of liquids)

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Expansion Thermometers

• Gas Thermometer
• (Expansion of gas)

• Depends on ideal gas law
• Nitrogen acts like a perfect gas at extremely low
  temperatures
• Inert and expensive
• It reacts with the steel bulb temperature at 427
  C

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Expansion Thermometers

• Filled Thermal Systems
• (Filled System Thermometer, Filled Bulb
  Thermometer)

• Similar operation as the liquid in glass
• Bulb
• Capillary tube
• Pressure element
• Scale

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Expansion Thermometers

• Filled Thermal System Classes
• (Filled System Thermometer, Filled Bulb
  Thermometer)

• 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

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Filled System Thermometers

• Gas filled thermometers
• liquid filled thermometers
• Mercury filled thermometers
• Vapor pressure thermometers
• Liquid inside the bulb continues to boil until
  the pressure in the system equals to vapor
  pressure of the boiling liquid.
• Liquid stops boiling unless its temperature
  increases.

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Expansion Thermometers

• Filled Thermal System Classes
• (Filled System Thermometer, Filled Bulb
  Thermometer)

• Temperature Range
• Mercury -38 F to 1200 F
• Xylene -40 to 750 F
• Alcohol -50 F to 300 F
• Ether 70 F to 195 F

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Electrical Temperature Instruments

• Thermocouple
• Thermistor
• Resistance thermometer

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Thermocouples
When 2 dissimilar metals are joined together to
form a junction, an emf is produced which is
proportional to the temperature being sensed.

• Seebeck Effect
• The generation of
• current in a circuit
• comprising of two wires
• of dissimilar metals in
• the presence of
• temperature difference

The magnitude of emf depends on the junction
temperature.
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Typical Industrial Thermocouple Assembly
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Thermocouple Types

• 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

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Metal Combinations
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-chromium Alumel
Nickel-aluminum Constantan Copper-nickel
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Thermocouple Tables
Voltage to Temperature Conversion
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
1.445 mV equal to temperature ..
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Thermocouple Callibration Charts
Voltage to Temperature Conversion
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Thermistors

• Thermistor, a word formed by combining thermal
  with resistor, is a temperature-sensitive
  resistor fabricated from semiconducting
  materials.
• The resistance of thermistors decreases
  proportionally with increases in temperature.
• The operating range can be -200C to 1000C

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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 other
  metals.

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Thermistors

• The word that best describes the thermistors is
  sensitive

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Thermistor Charts
Resistance to Temperature Conversion
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Thermistors

• 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

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Resistance Temperature Detector- RTD
Electrical Resistance Change (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.
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Electrical Resistance Change (RTD)
Platinum Wire RTDs (PRTs) PRTs have
established themselves as the de-facto industry
standard for temperature measurement, and for
many reasons

• linear temperature sensors
• Resistance vs temperature characteristics are
  stable and reproducible
• linear positive temperature coefficient (-200 to
  800 C)
• very accurate and suitable for use as a secondary
  standard

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Electrical Resistance Change (RTD)
Platinum Scale ( 0 to 100 C )
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Electrical Resistance Change (RTD)
International Practical scale for Temperature
(0 to 650. 30 C)
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Electrical Resistance Change (RTD)
International Practical scale for Temperature
(Below 0 C)
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Electrical Resistance Change (RTD)
International Practical scale for Temperature

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Electrical Resistance Change (RTD)
Other RTDs

• 10 ohms Copper RTD - .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 coefficients

All 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
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RTDs with a bridge circuit
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 copper lead
wire. Cu 0.0302 O per ft. How much error will
100 ft length of Cu lead wire introduce?
Most RTDs have an extra wire to compensate for
the length of lead wire.
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Radiation Pyrometer

• Radiation pyrometers

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Radiation Pyrometer

• Optical pyrometers (600 to 3000 C)

• 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

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Data Required to Provide Measurement of Process
Temperature
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Data Required to Provide Measurement of Process
Temperature
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Data Required to Provide Measurement of Process
Temperature
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Data Required to Provide Measurement of Process
Temperature
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Criteria for Selecting a Suitable Temperature
Measuring Instrument
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Summary of Temperature Sensor Characteristics
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Summary of Temperature Sensor Characteristics
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Assignment

1. Advantages and disadvantages of all temperature
   measuring instruments
2. Calibration of thermometers
3. Bimetallic thermometers
4. Liquid in glass thermometers
5. Thermocouples thermometers
6. Filled system thermometers
7. Resistance thermometers (RTD)
8. Radiation pyrometers
9. Optical pyrometers