1. Industrial Temperature
Measurement
Presented By:- Mr. Pravin Balakisan Biyani
Engineer (Operations- C & I)
Indiabulls Power Ltd., Amravati

2. Relative Scales Absolute Scales Fahrenheit (°F) Celsius (°C)
Temperature Measurement Scales
Relative Scales
Fahrenheit (°F)
Celsius (°C)
Absolute Scales
Rankine (°R)
Kelvin (K)
Conversions of various Scales
(°F) = 9/5*(°C) +32
(°C) = 5/9*[(°F) –32]
(°F) = (°R) –
(°C) = (K) –

3. Types of various temperature sensors
Thermocouples
Thermistors
Resistance Temperature Detector (RTD)
Pyrometers
Expansion of materials ( Bimetallic Devices )
Filled thermal Systems ( According to Scientific Apparatus Makers Association(SAMA) these are classified as liquid expansion, Mercury Expansion, vapor pressure, gas pressure)

5. Thermocouple
When two 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

6. Thermocouples Advantages Disadvantages Simple, Rugged
High temperature operation
Low cost
No resistance lead wire problems
Point temperature sensing
Fastest response to temperature changes
Least stable, least repeatable
Low sensitivity to small temperature changes
Extension wire must be of the same thermocouple type
Wire may pick up radiated electrical noise if not shielded
Lowest accuracy

7. Typical Industrial Thermocouple Assembly

8. Thermocouple Types
Base Metal Thermocouple: Base metal thermocouple types are composed of common, inexpensive metals such as nickel, iron and copper. The thermocouple types E, J, K, N and T are
among this group and are the most commonly used type of thermocouple. Each leg of these different thermocouples is composed of a special alloy, which is usually referred to by their common names.
Noble Metal Thermocouple (Type R, S, B): Noble metal thermocouples are manufactured with wire that is made with precious or “noble” metals like Platinum and Rhodium. Noble metal thermocouples are for use in oxidizing or inert applications and must be used with a ceramic protection tube surrounding the thermocouple element. These sensors are usually fragile and must not be used in applications that are reducing or in applications that contain metallic vapours.
Refractory Metal Thermocouple ( Type C, D, G): Refractory metal thermocouples are manufactured with wire that is made from the exotic metals tungsten and Rhenium. These metals are expensive, difficult to manufacture and wire made with these metals are very brittle. These thermocouples are intended to be used in vacuum furnaces at extremely high temperatures and must never be used in the presence of oxygen at temperatures above 500°F

9. 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 T
Blue/Red
0 to 400
Copper K
Yellow/Red
-270 to1372
Alumel R
Black/Red
-50 to 1768
Platinum-13% rhodium
Platinum S
Platinum-10% rhodium 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

11. Thermowells:
Protecting tubes or wells are supplied to protect the thermocouple from the harmful atmospheres, corrosive fluids or mechanical damages; to support the thermocouple or to permit thermocouple entry in the pressurized system.

12. Cold Junction Compensation
The temperature of the thermocouple’s reference junction must be known to get an accurate absolute-temperature reading.
When thermocouples were first used, this was done by keeping the reference junction in an ice bath(0°C).
This method was used to exhaustively characterize the various thermocouple types, thus almost all thermocouple tables use 0°C as the reference temperature.
But keeping the reference junction of the thermocouple in an ice bath is not practical for most measurement systems.
Instead most systems use a technique called reference-junction compensation,(also known as cold-junction compensation).
The reference junction temperature is measured with another temperature sensitive device—typically an IC, thermistor, diode, or RTD
The thermocouple voltage reading is then compensated to reflect the reference junction temperature.

13. 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 -200°C to °C

14. 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.

16. Small sizes and fast response Low cost Suitability for narrow spans
Thermistors
Advantages:
Small sizes and fast response
Low cost
Suitability for narrow spans
Disadvantages:
More susceptible to permanent de-calibration 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

17. 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 ohms at 0.0 °C.

18. 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

19. Various RTD configurations
2-Wire System
Two wire RTDs are used when the length of lead wire to the conditioning circuitry is small and does not introduce an additional resistance large enough to be measured by the bridge circuit. Depending on lead length and wire size the error may be negligible or profound.
3-Wire System
To compensate for errors introduced by the length of the lead wire industrial sensors commonly use this three-wire connection system. For this system to be effective, all the leads should be very near the same length and of the same gauge.
Any error introduced by the lead wire resistance is effectively cancelled in the bridge circuit and the only resistance change will be from the RTD.
4-Wire System
This system provides precision measurements. By switching the pairs of leads and averaging, you arrive at a value from which the lead resistance, thermal emf's in the leads and resistance changes in the leads due to ambient variation has been eliminated.

21. Expansion Thermometers
Bimetallic Thermometer (Expansion of solids)
Effect of unequal expansion of a bimetallic strip
Different metals have difference coefficient.
Configured as spiral or helix for compactness
- Can be used with a pointer to make an inexpensive compact rugged thermometer.

22. Bimetallic Thermometer

23. Filled Thermal Systems (Filled System Thermometer, Filled Bulb Thermometer)
Similar operation as the liquid in glass
Bulb
Capillary tube
Pressure element
Scale
Spiral Type Bourdon Tube

24. Filled Thermal System Classes
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
Temperature Range Response
Class l: F to F Slowest
Class ll: to 32 or 32 to 600 F Fastest
Class lll: F to F Fast
Class V: F to F Fast

25. Thanks