In this PPt u will see
1.Introduction
2.principle
3.construction
4.working
5.advantages and disadvantages
6.application
of Diaphragm and bellows pressure gauge
In this PPt u will see
1.Introduction
2.principle
3.construction
4.working
5.advantages and disadvantages
6.application
of Diaphragm and bellows pressure gauge
Gives a brief introduction about temperature measurement and its unit. it also enumerates the different techniques employed in temperature measurement.
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.
You'll find a wonderful explanation of the following topics:-
Sensing Elements,Bellows ,Bourdon tube,Impact of Operating Environment ,Diaphragm,Differen,capacitance,tial Pressure Transmitters,strain gauge
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
Gives a brief introduction about temperature measurement and its unit. it also enumerates the different techniques employed in temperature measurement.
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.
You'll find a wonderful explanation of the following topics:-
Sensing Elements,Bellows ,Bourdon tube,Impact of Operating Environment ,Diaphragm,Differen,capacitance,tial Pressure Transmitters,strain gauge
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
Following Devices are described. All the best !!!
Bourdon Gauge Tube
Diaphragms
Bellow Gauge
Piezoelectric Pressure Sensors
INDUCTIVE TRANSDUCERS
Pirani Gauge (One Wire)
Ionization gauge
In physics there are many variables which are of a non-electrical nature like pressure, force, speed, rotational frequency, acceleration or temperature.
When variables like these need to be measured and electronically processed, the non-electrical signal has to be converted into an electrical one.
For that reason sensors have been developed which alter their electrical properties as a function of the variable being measured. Photo resistors, for example, vary their resistance as a function of the light conditions, piezo-elements generate an electrical voltage when physical pressure is exerted on them.
The sought-after relationship between the variable being measured and the sensor's electrical property should always ideally be linear and valid over a wide range of values.
In reality linearity only exists in a certain value range and the sensors also operate only in a certain value range. Non-linearities can be corrected using circuit extensions or they can be resolved mathematically using calibration measurements based on the measured values (i.e. so-called characteristic matching). n order to measure non- electrical quantities, a detector i.e. sensing element is used which normally converts the physical quantities into a displacement. This displacement actuates electrical transducers which gives output which is electrical in nature. The simplest and cheapest way to measure displacement electrically in geomechanics applications is using a linear potentiometer. A linear potentiometer is simply a variable resistance. The resistor typically consists of a ceramic material that has an electric wire wound around it.
Unit-3 Instrumentation and control in mechanical engineering and other basic subject which contain instruments and their working under the syllabus of RGPV UNIVERSITY Bhopal.
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.
Overview of the fundamental roles in Hydropower generation and the components involved in wider Electrical Engineering.
This paper presents the design and construction of hydroelectric dams from the hydrologist’s survey of the valley before construction, all aspects and involved disciplines, fluid dynamics, structural engineering, generation and mains frequency regulation to the very transmission of power through the network in the United Kingdom.
Author: Robbie Edward Sayers
Collaborators and co editors: Charlie Sims and Connor Healey.
(C) 2024 Robbie E. Sayers
Welcome to WIPAC Monthly the magazine brought to you by the LinkedIn Group Water Industry Process Automation & Control.
In this month's edition, along with this month's industry news to celebrate the 13 years since the group was created we have articles including
A case study of the used of Advanced Process Control at the Wastewater Treatment works at Lleida in Spain
A look back on an article on smart wastewater networks in order to see how the industry has measured up in the interim around the adoption of Digital Transformation in the Water Industry.
Industrial Training at Shahjalal Fertilizer Company Limited (SFCL)MdTanvirMahtab2
This presentation is about the working procedure of Shahjalal Fertilizer Company Limited (SFCL). A Govt. owned Company of Bangladesh Chemical Industries Corporation under Ministry of Industries.
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/
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.
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.
Student information management system project report ii.pdfKamal Acharya
Our project explains about the student management. This project mainly explains the various actions related to student details. This project shows some ease in adding, editing and deleting the student details. It also provides a less time consuming process for viewing, adding, editing and deleting the marks of the students.
About
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
• Remote control: Parallel or serial interface.
• Compatible with MAFI CCR system.
• Compatible with IDM8000 CCR.
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
• Easy in configuration using DIP switches.
Technical Specifications
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
Key Features
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
• Remote control: Parallel or serial interface
• Compatible with MAFI CCR system
• Copatiable with IDM8000 CCR
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
Application
• Remote control: Parallel or serial interface.
• Compatible with MAFI CCR system.
• Compatible with IDM8000 CCR.
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
• Easy in configuration using DIP switches.
3. Pressure - Definition:
Defined as the amount of force applied to a surface or distributed over it and is measured as
force per unit area. (P = F/A)
Units of Pressure: The basic unit of pressure in SI units is the Pascal (Pa).
It is defined as force of 1 Newton (N) per square meter (m2). That is: 1 Pa = 1 N/m2.
High Pressure Unit
1 N/m2 = 1 Pa;
1 atm = 14.696 psi = 101.325 kPa
Low Pressure Unit
1 millibar = 100 dyne/cm2 = 14.5 * 10-3 psi
1 micron = 10-6 Hg = 19.34 * 10-6 psi
1 torr = 1 mm Hg = 19.34 * 10-3 psi
3
4. Relationship between Units
Relationship between Units
4
Pressure units
V
T
E
Pascal Bar
Technical
atmosphere
Standard
atmosphere
Torr
Pounds per
square inch
(Pa) (bar) (at) (atm) (Torr) (psi)
1 Pa ≡ 1 N/m2
10−5
1.0197×10−5
9.8692×10−6
7.5006×10−3
1.450377×10−4
1
bar
105
≡ 100 kPa
≡ 106
dyn/cm2
1.0197 0.98692 750.06 14.50377
1 at 0.980665×105
0.980665 ≡ 1 kp/cm2
0.9678411 735.5592 14.22334
1
atm
1.01325×105
1.01325 1.0332 1 ≡ 760 14.69595
1
Torr
133.3224 1.333224×10−3
1.359551×10−3
1.315789×10−3
≡ 1/760 atm
≈ 1 mm Hg
1.933678×10−2
1 psi 6.8948×103
6.8948×10−2
7.03069×10−2
6.8046×10−2
51.71493 ≡ 1 lbF /in2
11. Bourdon Tube
Elastic type Transducer
Cross-sectional tubing when deformed in any way will tend to regain its circular form
under the action of pressure.
Commonly used materials: phosphor-bronze, silicon-bronze, beryllium-copper, inconel,
and other C-Cr-Ni-Mo alloys
Range: 100,000 psi (700 MPa)
C – type Bourdon tube: 27 ° .
C – type, Helix type or spiral type.
11
12. Bourdon Tube
As the fluid pressure enters the bourdon tube, it tries to be reformed and because of a
free tip available, this action causes the tip to travel in free space and the tube unwinds.
The simultaneous actions of bending and tension due to the internal pressure make a
non-linear movement of the free tip.
This travel is suitable guided and amplified for the measurement of the internal pressure.
Types of Bourdon Tube
1. Spiral –Low range 10 –100 Kpa
2. C type –Medium range 100 – 5000 Kpa
3. Helical – High range 5000 – 20000 Kpa
12
13. Bourdon Tube – Pros & Cons
Advantages of Bourdon Tube
1. Low cost
2. Simple construction
3. Wide variety of ranges
4. High accuracy
Disadvantages of Bourdon Tube
1. Low spring gradient
2. Susceptible to shock and vibration
3. Susceptible to hysteresis
13
14. Diaphragm
Low pressure measurement.
Materials used: phosphor-bronze, silicon-bronze, beryllium-copper, inconel, and other
C-Cr-Ni-Mo alloys.
Non – metallic (slack diaphragm) has no elastic characteristics.
Make: Polythene, neoprene, silk, synthetic material.
Non – metallic, metallic.
Metallic has good spring characteristics.
Range: 50 Pa – 0.1 MPa
14
15. Diaphragm
Depends on following FACTORS:
1. Number and depth of corrugation
2. Number of capsules
3. Capsule diameter
4. Shell thickness
5. Material characteristics
15
16. Diaphragm - Principle
When a force acts against a thin stretched diaphragm, it causes a deflection of the
diaphragm with its centre deflecting the most.
Since the elastic limit has to be maintained, the deflection of the diaphragm must be kept
in a restricted manner.
This can be done by cascading many diaphragm capsules.
A main capsule is designed by joining two diaphragms at the periphery.
A pressure inlet line is provided at the central position.
When the pressure enters the capsule, the deflection will be the sum of deflections of all
the individual capsules.
16
17. Mc Leod Gauge
Vacuum Gauge with same principle as manometer.
Range: 10-4 Torr
Multiple compression technique.
𝑉
𝑑𝑝2
𝑑𝑡
= 𝐾(𝑝1 − 𝑝2)
V- Volume of the bulb
𝑑𝑝2
𝑑𝑡
= Pressure Gradient in time between the two elements
K – Flow conductance in the capillary.
17
18. Mc Leod Gauge
The gauge is used to compress a small quantity of low pressure gas to produce a
readable large pressure.
The McLeod gauge is independent of gas composition.
Bulb b of the gauge is attached to capillary aa’.
The mercury level in the gauge is lowered up to 𝑙1 by lowering the reservoir, thereby
allowing a little process fluid to enter b.
By raising the reservoir, the gas is now compressed in the capillary aa’ till mercury rises
to the zero mark in the side tube and capillary bb’.
The capillary bb’ is required to avoid any error due to capillary.
18
19. Pirani Gauge
When the pressure changes, there will be a change in current. For this, the voltage V has
to be kept constant.
The resistance R2 of the gauge is measured, by keeping the gauge current constant.
The null balance of the bridge circuit is maintained by adjusting the voltage or current.
An additional reference gauge can also be used in the adjacent arm of another pirani
gauge, in the bridge circuit.
19
20. Pirani Gauge
Fine wire of tungsten or platinum
0.02 cm in diameter.
Temperature range: (7-400) ° Celsius
Heating Current: 10 – 100 mA.
Range: 10-3 Torr to 1 Torr.
20
21. Ionization Gauge – Hot Cathode Type
A column of gas is introduced into which, a potential difference V is applied with free
electron in the space.
This causes the electron with a charge ‘e’ to acquire a kinetic energy 𝑉𝑒.
If the pressure range of the gas in the column goes below a certain limit, called the
critical pressure, then corresponding to a voltage larger than the critical voltage 𝑉𝑐, the
energy 𝑉𝑒 may be high enough to initiate ionization, and positive ions will be produced
when the electrons collide with the gas molecules.
The value of 𝑉𝑐 is smallest for Cesium (3.88V) and largest for Helium (24.58V), among
monoatomic gases or vapours.
For diatomic gases like N2, H2 and so on, it is roughly about 15V.
This is known as the ionization potential and at this potential the pressure is also
important.
21
22. Ionization Gauge – Hot Cathode Type
At very low pressures, during the intervals of time for transit from the cathode to the
plate in a vacuum chamber, more than one collision is unlikely for an electron.
Then for a fixed accelerating potential V > 𝑉𝑐, the number of positive ions formed would
vary linearly with the value of pressure.
Thus, a determination of the rate of production of positive ions for a given electron
current should give a measure of the pressure.
Range: Vacuum Range: 10-8 to 10-3 Torr.
Output current varying between 10-9 and 10-4 A.
22
23. Ionization Gauge – Hot Cathode Type
Schematic of Hot Cathode Tube
Pressure of Gas is proportional to
𝑃 =
1
𝑆
∗
𝐼 𝑃
𝐼 𝐺
• 𝐼 𝑃 = Plate Current
• 𝐼 𝑃 = Grid Current
• S = Sensitivity of gauge
23
P.C: Supervacoil
24. External Type Hot Ionisation Gauge
Hot cathode type ionization gauge consists of a basic vacuum triode.
The grid is at a large +ve potential with respect to the cathode and the plate.
The plate is at a -ve potential with respect to the cathode.
This method is known as the external control type ionization gauge as the +ve ion
collector is external to the electron collector grid with reference to the cathode.
The +ve ions available between the grid and the cathode will be drawn by the cathode,
and those between the grid and the plate will be collected by the plate.
24
25. Internal Type Hot Ionisation Gauge
Here the grid is the positive ion collector and the plate is the electron collector.
It consists of a helical grid with a potential of +150 volts.
This huge potential attracts the electrons and thus causes gas ionization.
At -30 volts, the gas ions are attracted to the central ion collector, thus producing an ion
current of 100 mA/Torr.
High current is passed through electrodes to stop increase of pressure.
Internal control type is a better option to measure pressure as low as 10-9 Torr.
Works at extreme high temperature and low pressure.
25
26. Ionization Gauge – Cold Cathode Type
Device consists of two cathodes and a hollow anode in between.
Input voltage greater than 2 Kilovolt is applied between them.
A strong magnetic field is produced due to the applied voltage and thus the electrons are
ejected.
At pressures below 10-2 Torr, the mean free path of the gas is so large that a collision
may not occur at all so that discharge is not sustained or ionization may not be initiated.
26
27. Ionization Gauge – Cold Cathode Type
Collimating magnetic field increases the path length for the electrons, enabling
discharges possible at pressures down to about 10-5 Torr.
Non – linear.
27
28. Dead Weight Piston Gauge
It is a force balancing pressure gauge.
Pressure easily converted to force with introduction of surface area.
It is used in calibration purposes for bellows and diaphragms.
It is used in higher steady pressure measurement.
It is a continuous balancing system.
The units of measurement are force and area.
It is mostly linear.
Accuracy < 0.1 %
Range up to 300 psig.
28
29. Dead Weight Piston Gauge - Principle
It consists of a very accurately machined, bored and finished piston which is inserted
into a close-fitting cylinder.
The area of cross section of both the piston and cylinder are known.
A platform is provided at the top of the piston where standard and accurate weights are
placed.
An oil reservoir with check valve is provided at the bottom.
The oil can be sucked by displacement pumps on its upward stroke.
29
30. Dead Weight Piston Gauge - Principle
For calibration, a known weight is first placed on the platform and fluid pressure is
applied on the other end of the piston until enough force is developed to lift the piston
weight combination and the piston floats freely within the cylinder between limit stops.
30
31. Capacitive Pressure Transducer
Consists of a parallel plate capacitors coupled with a diaphragm, usually metal and
exposed to the process pressure on one side and the reference pressure on the other side.
Electrodes are attached to the diaphragm and are charged by a high frequency oscillator.
The electrodes sense any movement of the diaphragm and this changes the capacitance.
The change of the capacitance is detected by an attached circuit which then outputs a
voltage according to the pressure change.
This type of sensor can be operated in the range of 2.5 Pa - 70MPa with a sensitivity of
0.07 MPa.
31
32. Capacitive Pressure Transducer
The principle of operation of capacitive pressure transducers is based upon the
familiar capacitance equation of the parallel plate capacitor
𝐶 =
∈0∈ 𝑟 𝐴
𝑑
C = capacitance in Farad; A= area of each plate (m2); d= distance between plates
(m); ɛ0 = 8.854 * 10-12 Farad/m2; ɛr = dielectric constant
The capacitance of the parallel plate varies inversely with the distance between
them.
With increase in pressure, the distance d (of the diaphragm) becomes less and
therefore C is increased and vice versa.
Hence the bridge is unbalanced and a current flows which gives a measure of
the change of pressure.
32
33. Capacitive Pressure Transducer
Advantages:
1. Gives out rapid response to changes in pressure
2. It can withstand a lot of vibration and shock
3. It is extremely sensitive
4. Offers a good frequency response
Disadvantages:
1. Metallic parts need insulation from each other
2. Affected by dirt and other contaminants
3. Temperature causes error.
33
34. Piezo Electric Pressure Transducer
Piezoelectric characteristics of certain crystalline materials are used.
Electricity is generated when pressure is applied.
Some of these materials are Barium Titanate Sintered powder, quartz, tourmaline,
Rochelle salt.
The main advantages of these crystals are that they have high mechanical and thermal
state capability, capability of withstanding high order of strain, low leakage, and good
frequency response.
Each crystal has three sets of axes – Optical axes, three electrical axes OX1, OX2, and
OX3 with 120 degree with each other, and three mechanical axes OY1, OY2 and OY3
also at 120 degree with each other.
The mechanical axes will be at right angles to the electrical axes.
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35. Piezo Electric Pressure Transducer
Some of the parameters that decide the nature of the crystal for the application are
1. Angle at which the wafer is cut from natural quartz crystal
2. Plate thickness
3. Dimension of the plate
4. Means of mounting
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36. Piezo Electric Pressure Transducer
Advantages of Piezo electric Pressure Transducer
1. Very high frequency response.
2. Self-generating, so no need of external source.
3. Simple to use as they have small dimensions and large measuring range.
4. It has a large dielectric constant. The crystal axis is selectable by orienting the
direction of orientation.
Disadvantages of Piezo electric Pressure Transducer
1. It is not suitable for measurement in static condition.
2. Since the device operates with the small electric charge, they need high impedance
cable for electrical interface.
3. The output may vary according to the temperature variation of the crystal.
4. The relative humidity rises above 85% or falls below 35%, its output will be
affected. If so, it has to be coated with wax or polymer material.
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