Gives a brief introduction about temperature measurement and its unit. it also enumerates the different techniques employed in temperature measurement.
Resistance Temperature Detector
WHAT IS RTD ?
WHY IS RTD USED?
Typical Design
RTD PROBE
Common Resistance materials for RTD
Advantages of RTD
Application OF RTD
Question and Answers
Usage of Platinum
This Presentation can be used by the Students of Engineering who Deals with the Subject INDUSTRIAL INSTRUMENTATION and use it for Refrence (Anyways you Guys will Copy Paste or Download it) ;)
esistance thermometers, also called resistance temperature detectors (RTDs), are sensors used to measure temperature. Many RTD elements consist of a length of fine wire wrapped around a ceramic or glass core but other constructions are also used. The RTD wire is a pure material, typically platinum, nickel, or copper. The material has an accurate resistance/temperature relationship which is used to provide an indication of temperature. As RTD elements are fragile, they are often housed in protective probes.
Resistance thermometers are constructed in a number of forms and offer greater stability, accuracy and repeatability in some cases than thermocouples. While thermocouples use the Seebeck effect to generate a voltage, resistance thermometers use electrical resistance and require a power source to operate. The resistance ideally varies nearly linearly with temperature per the Callendar–Van Dusen equation.
The platinum detecting wire needs to be kept free of contamination to remain stable. A platinum wire or film is supported on a former in such a way that it gets minimal differential expansion or other strains from its former, yet is reasonably resistant to vibration. RTD assemblies made from iron or copper are also used in some applications. Commercial platinum grades exhibit a temperature coefficient of resistance 0.00385/°C (0.385%/°C) (European Fundamental Interval).[7] The sensor is usually made to have a resistance of 100 Ω at 0 °C. This is defined in BS EN 60751:1996 (taken from IEC 60751:1995). The American Fundamental Interval is 0.00392/°C,[8] based on using a purer grade of platinum than the European standard. The American standard is from the Scientific Apparatus Manufacturers Association (SAMA), who are no longer in this standards field. As a result, the "American standard" is hardly the standard even in the US.
Lead-wire resistance can also be a factor; adopting three- and four-wire, instead of two-wire, connections can eliminate connection-lead resistance effects from measurements (see below); three-wire connection is sufficient for most purposes and is an almost universal industrial practice. Four-wire connections are used for the most precise applications.
A thermocouple is a temperature-measuring device consisting of two dissimilar conductors that contact each other at one or more spots. It produces a voltage when the temperature of one of the spots differs from the reference temperature at other parts of the circuit.
1. THERMOCOUPLE
∙ Principle of Operation
∙ Materials Used
∙ Advantages
∙ Applications
∙ Comparison with RTD
∙ Limitations
By
AnandBongir
GirjashankarMishra
2. A thermocouple is a junction between two different metals that produces a voltage related to a temperature difference.
3. Principle of Operation
Thermocouples are based on the principle that two wires made of dissimilar materials connected at either end will generate a potential between the two ends that is a function of the materials and temperature difference between the two ends (also called the Seebeck Effect).
4. Seebeck Effect
5.
6. Materials Used
Type K:
Chromel – Alumel
• Range: −200 °C to +1350 °C
• Sensi: 41 µV/°C
Type J:
Iron – Constantan
• −40 to +750 °C
• 55 µV/°C
Type E:
Chromel – Constantan
• 401 to 900° C
• 68 µV/°C
Type N:
Nicrosil – Nisil
• >1200 °C
• 39 µV/°C
7. Advantages
It is rugged in construction
Covers a wide temperature range
Using extension leads and compensating cables, long transmission distances for temperature measurement possible. This is most suitable for temperature measurement of industrial furnaces
Comparatively cheaper in cost
Calibration can be easily checked
Offers good reproducibility
High speed of response
Satisfactory measurement accuracy
8. Limitations
For accurate temperature measurements, cold junction compensation is necessary
The emf induced versus temperature characteristics is somewhat nonlinear
Stray voltage pickup is possible
In many applications, amplification of signal is required
9. Applications
Type B, S, R and K thermocouples are used extensively in the steel and iron industries to monitor temperatures and chemistry throughout the steel making process.
Gas-fed heating appliances such as ovens & water heaters.
In the testing of prototype electrical and mechanical apparatus
Discussing what is temperature. How to calibrate a thermometer. Liquid in glass thermometers. Calibrate a liquid-in-glass thermometer using two fixed points. Characteristics of a quality/ good thermometer.
Resistance Temperature Detector
WHAT IS RTD ?
WHY IS RTD USED?
Typical Design
RTD PROBE
Common Resistance materials for RTD
Advantages of RTD
Application OF RTD
Question and Answers
Usage of Platinum
This Presentation can be used by the Students of Engineering who Deals with the Subject INDUSTRIAL INSTRUMENTATION and use it for Refrence (Anyways you Guys will Copy Paste or Download it) ;)
esistance thermometers, also called resistance temperature detectors (RTDs), are sensors used to measure temperature. Many RTD elements consist of a length of fine wire wrapped around a ceramic or glass core but other constructions are also used. The RTD wire is a pure material, typically platinum, nickel, or copper. The material has an accurate resistance/temperature relationship which is used to provide an indication of temperature. As RTD elements are fragile, they are often housed in protective probes.
Resistance thermometers are constructed in a number of forms and offer greater stability, accuracy and repeatability in some cases than thermocouples. While thermocouples use the Seebeck effect to generate a voltage, resistance thermometers use electrical resistance and require a power source to operate. The resistance ideally varies nearly linearly with temperature per the Callendar–Van Dusen equation.
The platinum detecting wire needs to be kept free of contamination to remain stable. A platinum wire or film is supported on a former in such a way that it gets minimal differential expansion or other strains from its former, yet is reasonably resistant to vibration. RTD assemblies made from iron or copper are also used in some applications. Commercial platinum grades exhibit a temperature coefficient of resistance 0.00385/°C (0.385%/°C) (European Fundamental Interval).[7] The sensor is usually made to have a resistance of 100 Ω at 0 °C. This is defined in BS EN 60751:1996 (taken from IEC 60751:1995). The American Fundamental Interval is 0.00392/°C,[8] based on using a purer grade of platinum than the European standard. The American standard is from the Scientific Apparatus Manufacturers Association (SAMA), who are no longer in this standards field. As a result, the "American standard" is hardly the standard even in the US.
Lead-wire resistance can also be a factor; adopting three- and four-wire, instead of two-wire, connections can eliminate connection-lead resistance effects from measurements (see below); three-wire connection is sufficient for most purposes and is an almost universal industrial practice. Four-wire connections are used for the most precise applications.
A thermocouple is a temperature-measuring device consisting of two dissimilar conductors that contact each other at one or more spots. It produces a voltage when the temperature of one of the spots differs from the reference temperature at other parts of the circuit.
1. THERMOCOUPLE
∙ Principle of Operation
∙ Materials Used
∙ Advantages
∙ Applications
∙ Comparison with RTD
∙ Limitations
By
AnandBongir
GirjashankarMishra
2. A thermocouple is a junction between two different metals that produces a voltage related to a temperature difference.
3. Principle of Operation
Thermocouples are based on the principle that two wires made of dissimilar materials connected at either end will generate a potential between the two ends that is a function of the materials and temperature difference between the two ends (also called the Seebeck Effect).
4. Seebeck Effect
5.
6. Materials Used
Type K:
Chromel – Alumel
• Range: −200 °C to +1350 °C
• Sensi: 41 µV/°C
Type J:
Iron – Constantan
• −40 to +750 °C
• 55 µV/°C
Type E:
Chromel – Constantan
• 401 to 900° C
• 68 µV/°C
Type N:
Nicrosil – Nisil
• >1200 °C
• 39 µV/°C
7. Advantages
It is rugged in construction
Covers a wide temperature range
Using extension leads and compensating cables, long transmission distances for temperature measurement possible. This is most suitable for temperature measurement of industrial furnaces
Comparatively cheaper in cost
Calibration can be easily checked
Offers good reproducibility
High speed of response
Satisfactory measurement accuracy
8. Limitations
For accurate temperature measurements, cold junction compensation is necessary
The emf induced versus temperature characteristics is somewhat nonlinear
Stray voltage pickup is possible
In many applications, amplification of signal is required
9. Applications
Type B, S, R and K thermocouples are used extensively in the steel and iron industries to monitor temperatures and chemistry throughout the steel making process.
Gas-fed heating appliances such as ovens & water heaters.
In the testing of prototype electrical and mechanical apparatus
Discussing what is temperature. How to calibrate a thermometer. Liquid in glass thermometers. Calibrate a liquid-in-glass thermometer using two fixed points. Characteristics of a quality/ good thermometer.
this section speaks about the quantity flow meter and its different types i.e. positive displacement flow meter and metering pump, it comprises discussion on mass flow meter, coriolis flow meter, variable reluctance tacho generator and linear resistance element flow meter.
This slide comprises a very rudimentary introduction of Industrial Instrumentation.
These slides may help students understand the aspects the Industrial Instrumentation.
These slides provide an elementary description of Power Electronics and its application domains. It also shows the different power devices and converters.
Speaks about the different aspects of flow measurement i.e. flow types, fluid types, its units, selection parameters; definition of common terms, coanda effect coriolis effect . it also speaks about the factors affecting flow measurement.
this article covers discussion of variable area flow meter. also it speaks about turbine flow meter, target flow meter, magnetic flow meter, vortex flow meter, ultrasonic flow meter, thermal flow meter.
it speaks about the differential head flow meters. its different types. their principle of operation, venturi meter, orifice plate, rotameters, it also covers discussion on open channel flow meter. it covers the different application domains of the different types of flow meters and their advantages and disadvantages.
This article discusses different power electronics devices that are in use like power diodes, power thyristors, power transistors, IGBT, GTO, IGCT and others. This article will give a basic view of these devices and their operations.
This article speaks about the different energy domains, sensors, actuation techniques, transduction techniques, fabrication materials, physical strength requirements, substrate materials and De Vries formula used in MEMS technology.
This article discusses MEMS, i.e. Micro-Electro Mechanical Systems.
It gives a rudimentry idea of MEMS technology, its block diagram, applications, advantages and disadvantages. It also gives a brief idea on the working principle of MEMS devices.
Basic concept and techniques of Flow measurement are described.
Bernoulli's Principle, Hagen Poiseuille Law, Coanda and Coriolis Effect are described..
This article describes the operational principles, construction and other features of the four most basic transducers viz. Strain Gauge, Potentiometer, Load Cell and LVDT. Also this article describes the characteristic features of different material transduction properties.
Hierarchical Digital Twin of a Naval Power SystemKerry Sado
A hierarchical digital twin of a Naval DC power system has been developed and experimentally verified. Similar to other state-of-the-art digital twins, this technology creates a digital replica of the physical system executed in real-time or faster, which can modify hardware controls. However, its advantage stems from distributing computational efforts by utilizing a hierarchical structure composed of lower-level digital twin blocks and a higher-level system digital twin. Each digital twin block is associated with a physical subsystem of the hardware and communicates with a singular system digital twin, which creates a system-level response. By extracting information from each level of the hierarchy, power system controls of the hardware were reconfigured autonomously. This hierarchical digital twin development offers several advantages over other digital twins, particularly in the field of naval power systems. The hierarchical structure allows for greater computational efficiency and scalability while the ability to autonomously reconfigure hardware controls offers increased flexibility and responsiveness. The hierarchical decomposition and models utilized were well aligned with the physical twin, as indicated by the maximum deviations between the developed digital twin hierarchy and the hardware.
Saudi Arabia stands as a titan in the global energy landscape, renowned for its abundant oil and gas resources. It's the largest exporter of petroleum and holds some of the world's most significant reserves. Let's delve into the top 10 oil and gas projects shaping Saudi Arabia's energy future in 2024.
Final project report on grocery store management system..pdfKamal Acharya
In today’s fast-changing business environment, it’s extremely important to be able to respond to client needs in the most effective and timely manner. If your customers wish to see your business online and have instant access to your products or services.
Online Grocery Store is an e-commerce website, which retails various grocery products. This project allows viewing various products available enables registered users to purchase desired products instantly using Paytm, UPI payment processor (Instant Pay) and also can place order by using Cash on Delivery (Pay Later) option. This project provides an easy access to Administrators and Managers to view orders placed using Pay Later and Instant Pay options.
In order to develop an e-commerce website, a number of Technologies must be studied and understood. These include multi-tiered architecture, server and client-side scripting techniques, implementation technologies, programming language (such as PHP, HTML, CSS, JavaScript) and MySQL relational databases. This is a project with the objective to develop a basic website where a consumer is provided with a shopping cart website and also to know about the technologies used to develop such a website.
This document will discuss each of the underlying technologies to create and implement an e- commerce website.
CFD Simulation of By-pass Flow in a HRSG module by R&R Consult.pptxR&R Consult
CFD analysis is incredibly effective at solving mysteries and improving the performance of complex systems!
Here's a great example: At a large natural gas-fired power plant, where they use waste heat to generate steam and energy, they were puzzled that their boiler wasn't producing as much steam as expected.
R&R and Tetra Engineering Group Inc. were asked to solve the issue with reduced steam production.
An inspection had shown that a significant amount of hot flue gas was bypassing the boiler tubes, where the heat was supposed to be transferred.
R&R Consult conducted a CFD analysis, which revealed that 6.3% of the flue gas was bypassing the boiler tubes without transferring heat. The analysis also showed that the flue gas was instead being directed along the sides of the boiler and between the modules that were supposed to capture the heat. This was the cause of the reduced performance.
Based on our results, Tetra Engineering installed covering plates to reduce the bypass flow. This improved the boiler's performance and increased electricity production.
It is always satisfying when we can help solve complex challenges like this. Do your systems also need a check-up or optimization? Give us a call!
Work done in cooperation with James Malloy and David Moelling from Tetra Engineering.
More examples of our work https://www.r-r-consult.dk/en/cases-en/
Water scarcity is the lack of fresh water resources to meet the standard water demand. There are two type of water scarcity. One is physical. The other is economic water scarcity.
1. TEMPERATURE
MEASUREMENT
PART I of II
ER. FARUK BIN POYEN, Asst. Professor
DEPT. OF AEIE, UIT, BU, BURDWAN, WB, INDIA
faruk.poyen@gmail.com
2. Contents:
Temperature Scales
Fahrenheit and Centigrade
Kelvin and Rankine
Reaumur
International Practical Temperature Scale
Methods of Temperature Measurement
Expansion Thermometer
Bimetallic Thermometer (Expansion of Solid)
Liquid in Glass Thermometer (Expansion of Liquid)
Liquid in Metal Thermometer (Expansion of Liquid)
Gas Thermometer
Filled System Thermometer
Liquid filled Thermometer
Mercury filled Thermometer
Vapour pressure Thermometer
2
3. Temperature Measurement:
Temperature is defined as the condition of a body by virtue of which heat is transferred
to and from other bodies. The degree of hotness or coldness of a body or an
environment is measured on a definite scale.
Temperature cannot be measured directly but must be measured by observing the effect
that temperature variation causes on the measuring device. The methods are broadly
classified into three classes.
Non – Electrical
Electrical
Radiation
3
4. Temperature Scales:
Absolute Temperature (Kelvin scale): K = °C + 273.15,
°C being temperature in Celsius scale.
Absolute Scale (Rankine scale): R = °F + 459.69,
°F being temperature in Fahrenheit scale.
[
𝑇2
𝑇1
] 𝑅𝑎𝑛𝑘𝑖𝑛𝑒= [
𝑇2
𝑇1
] 𝐾𝑒𝑙𝑣𝑖𝑛
℉ = 32 +
9
5
℃ ≡
℃
100
=
℉−32
180
R =
9
5
K
Reaumur Scale: R’ assigns 0° R’ to the ice – point and 80° R’ to the steam – point and often finds use in
alcohol industry.
Lower fixed point or ice – point is the temperature of ice prepared from distilled water at 760 mm of
mercury.
Upper fixed point or steam – point is the temperature of steam prepared from distilled water boiling at 760
mm of mercury.
4
5. Basic Fixed Points:
Boiling Point: The temperature at which substance changes from liquid
to gas.
Freezing Point: The temperature at which substance changes from liquid
to solid.
Triple Point: A particular temperature and pressure at which three
different phases of one substance can exist in equilibrium. According to
Gibb’s phase rule, a three – phase situation in a component leaves it
with no degrees of freedom.
Absolute Zero: The temperature at which molecular motion completely
ceases.
5
6. Important Laws in Temperature Measurement
Mentioned below are few of the rudimentary laws that find applications
in the measurement process of temperature. These laws show correlation
between temperature and potential differences.
Seebeck Effect
Peltier Effect
Thompson Effect
Thermoelectric Effect
Law of Homogeneous Material
Law of Intermediate Metal
Law of Intermediate Temperature
6
7. Thermoelectric Effect
The thermoelectric effect is the direct conversion of temperature differences to
electric voltages and vice versa.
A thermoelectric device creates voltage when there is a different temperature on each
side. Conversely, when a voltage is applied to it, it creates a temperature difference. At
the atomic scale, an applied temperature gradient causes charge carriers in the material
to diffuse from the hot side to the cold side.
This effect can be used to generate electricity, measure temperature or change the
temperature of objects. As the direction of heating and cooling is determined by the
polarity of the applied voltage, thermoelectric devices can be used as temperature
controllers.
The term "thermoelectric effect" encompasses three separately identified effects: the
Seebeck effect, Peltier effect, and Thomson effect.
The Peltier–Seebeck and Thomson effects are thermodynamically reversible.
7
8. Seebeck Effect
The Seebeck effect: Temperature difference between two dissimilar electrical
conductors or semiconductors produces a voltage difference between them.
The Seebeck effect is the conversion of temperature differences directly
into electricity.
The local current density J is given by
𝑱 = 𝝈(−𝛁𝑽 + 𝑬 𝒆𝒎𝒇)
where V is the local voltage and σ is the local conductivity.
In general, the Seebeck effect is described locally by the creation of an electromotive
field
𝑬 𝒆𝒎𝒇 = −𝑺𝛁𝑻
where S is the Seebeck coefficient (also known as thermo power), a property of the local
material, and 𝛻𝑇 is the gradient in temperature T.
8
10. Peltier Effect
The Peltier effect is a temperature difference created by applying a voltage between
two electrodes connected to a sample of semiconductor material. This phenomenon can
be useful when it is necessary to transfer heat from one medium to another on a small
scale.
The Peltier heat generated at the junction per unit time, Q, is equal to
𝑄 = (𝛱𝐴 − 𝛱 𝐵)𝐼
where 𝛱𝐴 (𝛱 𝐵) is the Peltier coefficient of conductor A (B), and I is the electric current
(from A to B). Note that the total heat generated at the junction is not determined by the
Peltier effect alone, as it may also be influenced by Joule heating and thermal gradient
effects.
10
12. Thomson Effect
Thermoelectric couples: Consist of positive and negative elements connected
electrically in series and parallel in heat flow.
Thomson Effect: The Thomson effect describes the heating or cooling of a current
carrying conductor with a temperature gradient.
Consider a conductor which is subject to the longitudinal temperature gradient and also to
the potential difference such that there is a flow of current and heat in conductor. The
Thomson effect describes the mechanism that a current flowing in a wire in which a
temperature gradient is present shows a heat exchange with its environment.
𝑸 = 𝑲𝑱𝛁𝑻, 𝑲 = 𝑻
𝒅𝑺
𝒅𝑻
,
where K = Thomson coefficient, J = current density and 𝛻𝑇 = temperature gradient. S =
Seeback coefficient
12
13. Laws of Thermoelectricity
Law of Homogeneous Materials: - A thermoelectric current cannot be sustained in a
single homogeneous material by the application of heat alone, regardless of how much
it might vary in cross-section.
Law of Intermediate Material: - The algebraic sum of thermoelectric forces in circuit
composed of any number of dissimilar materials is Zero if all of the circuit is at same
temperature.
Law of Successive or Intermediate Temperature: - If two dissimilar homogeneous
materials produce thermal (emf)1 when the junctions are T1 and T2 and produce
thermal (emf)2 when the junction are at T2 and T3, the emf generated when the junction
are at temperature T1 and T3 will be (emf)1 + (emf)2.
13
15. Methods of Temperature Measurement
Expansion Thermometer
Bimetallic Thermometer
(Expansion of Solid)
Liquid in Glass Thermometer
(Expansion of Liquid)
Liquid in Metal Thermometer
(Expansion of Liquid)
Gas Thermometer
Filled System Thermometer
Liquid filled Thermometer
Mercury filled Thermometer
Vapour pressure Thermometer
Electrical Temperature Instrument
Resistance Thermometer
Thermocouple
Thermistor
Thermopile
Pyrometer
Radiation Pyrometer
Optical Pyrometer
Other Methods of Temperature Measurement
Quartz Thermometer
Solid State Temperature Measurement
Optical Fibre Temperature Measurement
Ultrasonic Thermometer
15
16. Expansion Methods of Measurement
Bimetallic Thermometer (Expansion of Solid)
Liquid in Glass Thermometer (Expansion of Liquid)
Liquid in Metal Thermometer (Expansion of Liquid)
Gas Thermometer
16
17. Bimetallic Thermometer (Expansion of Solid)
Made up of bimetallic strips formed by joining two different metals having different
thermal expansion coefficients.
Basically, bimetallic strip is a mechanical element which can sense temperature and
transform it into a mechanical displacement.
This mechanical action from the bimetallic strip can be used to activate a switching
mechanism for getting electronic output.
Also it can be attached to the pointer of a measuring instrument or a position indicator.
Various techniques such as riveting, bolting, fastening can be used to bond two layers
of diverse metals in a bimetallic strip.
However the most commonly used method is welding.
Since two metals are employed to construct a bimetallic strip, hence they are named so.
17
18. Bimetallic Strip: Working Principle
Different metals expand at different rates as they warm up.
Two dissimilar metals behave in a different manner when exposed to temperature
variations owing to their different thermal expansion rates.
One layer of metal expands or contracts more than the other layer of metal in a
bimetallic strip arrangement which results in bending or curvature change of the strip.
One end of a straight bimetallic strip is fixed in place. As the strip is heated, the other
end tends to curve away from the side that has the greater coefficient of linear
expansion.
18
19. Bimetallic Strip: Features
Range: -103 ° F to 1000 ° F (-75 ° C – 540 ° C)
Advantages:
Low cost
Tough
Easy installation and maintenance
Good accuracy
Wide temperature range
Disadvantages:
Limited to local mounting
Only indicating type
Calibration may change due to rough handling
Accuracy is not the best
19
20. Liquid-In-Glass Thermometers
It mainly comprises:
A bulb which acts as a container for the functioning liquid where it can easily expand
or contract in capacity.
A stem, “a glass tube containing a tiny capillary connected to the bulb and enlarged at
the bottom into a bulb that is partially filled with a working liquid”.
A temperature scale which is basically preset or imprinted on the stem for displaying
temperature readings.
Point of reference i.e. a calibration point which is most commonly the ice point.
A working liquid which is generally either mercury or alcohol.
An inert gas, mainly argon or nitrogen which is filled inside the thermometer above
mercury to trim down its volatilization.
20
21. Liquid-In-Glass Thermometers - Principle
The principle used to measure temperature is that of the apparent
thermal expansion of the liquid.
It is the difference between the volumetric reversible thermal expansion
of the liquid and its glass container that makes it possible to measure
temperature.
21
22. Liquid-In-Glass Thermometers - Features
Range of -200 °C to 600°C.
Advantages:
Comparatively cheaper
Handy and convenient to use.
They do not necessitate power supply or batteries for charging.
They can be frequently applied in areas where there is problem of electricity.
Very good repeatability and calibration remains unaffected
Limitations:
Not very accurate
Short temperature range
Weaker and more delicate than electrical thermometers
Subject to parallax error
22
23. Liquid in Metal Thermometer
A thermometer in which the thermally sensitive element is a liquid contained in a metal
envelope, frequently in the form of a Bourdon tube.
A liquid in metal thermometer in which mercury has been used as liquid and the metal
is steel.
This mercury-in-steel thermometer works on exactly the same principle as the liquid-
in-glass thermometer.
The glass bulb is replaced by a steel bulb and the glass capillary tube by one of
stainless steel.
As mercury in the system is not visible, a Bourdon tube is used to measure the change
in its volume.
23
24. Liquid in Metal Thermometer - Principle
When the temperature to be measured rises, the mercury in the bulb expands more than
the bulb so that some mercury is driven through the capillary tube into the Bourdon
tube.
As the temperature continues to rise, increasing amounts of mercury will be driven into
the Bourdon tube, causing it to bend.
One end of the Bourdon tube is fixed, while the motion of the other end is
communicated to the pointer which moves on a calibrated temperature scale.
24
25. Liquid in Metal Thermometer
The thermometer bulb is also placed in a protective pocket where the gas or liquid
whose temperature is being measured, is at a pressure other than atmospheric.
In this case the pocket prevents the bulb being subjected to this pressure and also
enables the bulb to be changed without shutting down the plant.
The capillary tube used in the mercury-in-steel thermometer is usually made from
stainless steel, as mercury will combine with other metals.
Changes of temperature affect the capillary and the mercury it contains, and hence the
thermometer reading.
Generally, mercury is used as a liquid. But it has its limitations, particularly at the
lower end of the temperature scale.
For this and other reasons, other liquids are also used sometimes in place of mercury.
25
26. Gas Filled Thermometer
The filled thermal device consists of a primary element that takes the form of a
reservoir or bulb, a flexible capillary tube, and a hollow Bourdon tube that actuates a
signal-transmitting device and/or a local indicating temperature dial.
The filling fluid, either liquid or gas, expands as temperature increases.
This causes the Bourdon tube to uncoil and indicate the temperature on a calibrated
dial.
The filling or transmitting medium is a vapour, a gas, mercury, or another liquid.
The liquid-filled system is the most common because it requires a bulb with the
smallest volume or permits a smaller instrument to be used.
26
27. Gas Filled Thermometer
The gas-filled system uses the perfect gas law, which states the following for an ideal
gas:
T = k P V, where:
T = temperature; k = constant; P = pressure; V = volume;
If the volume of gas in the measuring instrument is kept constant, then the ratio of the
gas pressure and temperature is constant, so that
27
28. Filled System Thermometer
Filled system thermometers consist of Bourdon tube, a capillary tube and a
thermometer bulb all interconnected.
The entire point is sealed after appropriate liquid filling at NTP and commonly used
liquids are mercury, ethyl alcohol, xylene and toluene.
Liquid expands or contracts with gain or loss of heat till measured temperature is
attained leading to the expansion or contraction of the Bourdon tube which
subsequently moves a pointer for indication.
Types are:
Gas filled (Gas Filled Thermometers)
Liquid filled
Mercury filled
Vapour filled
28
29. Filled System Thermometer
Liquid Filled Thermometer: They work on the principle of liquid expansion with temperature
rise. The filling liquid is usually an inert hydrocarbon viz. xylene which has six times more
expansion co-efficient than mercury decreasing the bulb position. One criterion to be maintained
is that the pressure inside must be greater than the vapour pressure of liquid to prevent formation
of bubbles inside. Solidification of liquid is also not permitted.
Mercury Filled Thermometer: Similar to that of liquid filled thermometers but provides rapid
response, accuracy and plenty of power. Pressure is as high as 1200 psig to as low as 400 psig.
The high pressure reduces the head effect. They are normally contained in stainless steel bulb
increasing the corrosion resistance.
Vapour Filled Thermometer: Here the bulb is partially filled with liquid and partially with
vapour. Some of the liquid vaporises during operation. The liquid inside boils and vaporises
creating gas inside the system. The liquid continues to boil until pressure balance is obtained
between systems and vapour pressure. Here liquid stops boiling unless temperature rises.
Similarly, when temperature drops, liquid and vapour inside also cool causing some vapour to
condense, bringing down the pressure inside. When pressure inside equals vapour pressure, this
action stops. Due to changes in pressure, bourdon tube uncoils or tightens with increase or
decrease of pressure indicating temperature on a pointer scale.
29
30. Filled System Thermometer - Features
Sources of Error in Filled – System Thermometers:
Ambient temperature effect
Head or elevation effect
Barometric effect
Immersion effect
Radiation effect
Advantages of Filled System Thermometer
Rugged construction
Low maintenance
No electric power requirement
Satisfactory time response
Low cost
Capillary allows considerable separation between measurement point and temperature point
Disadvantages of Filled System Thermometers:
Large bulb required for better accuracy
Requires full scale replacement if found faulty
Accuracy, sensitivity and span are on the lower side compared to electrical methods
Not great temperature range ability
30
31. References:
Chapter 13: Temperature Measurement, “Industrial Instrumentation and Control” by S
K Singh. Tata McGraw Hill, 3rd Edition. 2009, New Delhi. ISBN-13: 978-0-07-
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Chapter 11: Temperature Measurement, “Instrumentation, Measurement and
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