SlideShare a Scribd company logo
1 of 40
Download to read offline
Indicating, Recording & Controlling Devices Used in Dairy Plants
Principle, Working Mechanisms & Applications
Subject : Instrumentation & Process Control (DE-525)
Submitted by : Dhruv Beladiya
M.Tech ( 2nd Semester )
Department of Dairy Engineering
CONTENTS
Introduction
Resistance Temperature Detectors (RTDs)
Effect of Temperature on Sorption Isotherm
Measurement of Sorption Isotherm
Bellows-Type Pressure Detectors
Thermistors
Thermocouples
Bourdon Tube-Type Pressure Detectors
Level Indicator - Float Sensor
Level Indicator - Ultrasonic Sensor
Magnetic Flow Meter
Ultrasonic Flow Meter
Conclusion
12-07-2020 2
INTRODUCTION
12-07-2020 3
• The most important properties of dairy processes subject to measurement that
reflect both process operation and product quality are classified as objective
or subjective.
• Examples of the former are pH, temperature, flow rates, pressure, level, etc.
• Sensors for on-line measurement of such properties have been available
already for a long time.
• Properties such as taste, flavour, colour and consistency are considered as
subjective and difficult to measure.
• Commercial sensors applied in the dairy industry are subject to several
quality constraints such as sanitary, safety and environmental requirements.
CONT.
12-07-2020 4
• A trend in the new sensor design technologies is the increasing integration of the
sensing elements into silicon chip microcircuits.
• These new measurement devices directly incorporate all circuitry needed to self-
compensate for environmental changes and yield an output that is suitably
amplified for transmission to standard electronic controllers.
• These sensors offer the advantage of small size, reduced prices and practically no
mechanical parts to wear out.
Resistance Temperature Detectors (RTDs)
12-07-2020 5
• A resistance temperature detector (abbreviated RTD) is basically either a long,
small diameter metal wire wound in a coil or an etched grid on a substrate, much
like a strain gage.
• Platinum is the most common metal used for RTDs.
12-07-2020 6
 Principle of Operation
• Resistance Temperature Detectors (RTD) operates on the principle that the
electrical resistance of a metal changes predictably in an essentially linear and
repeatable manner with changes in temperature.
• RTD have a positive temperature coefficient (resistance increases with
temperature).
• The resistance of the element at a base temperature is proportional to the length
of the element and the inverse of the cross-sectional area.
• A typical electrical circuit designed to measure temperature with RTDs actually
measures a change in resistance of the RTD, which is then used to calculate a
change in temperature.
• The resistance of an RTD increases with increasing temperature, just as the
resistance of a strain gage increases with increasing strain.
12-07-2020 7
 RTD Materials & Construction
• RTD acts somewhat like an electrical transducer, converting changes in
temperature to voltage signals by the measurement of resistance.
• The metals that are best suited for use as RTD sensors are pure metals or certain
alloys of uniform quality that increase in resistance as temperature increases and
conversely decrease in resistance as temperature decreases.
• Only a few metals have the properties necessary for use in RTD elements.
Common materials used in RTD sensor are BALCO wire, Copper, Platinum.
12-07-2020 8
• This particular design has a platinum element that is surrounded by a porcelain
insulator. The insulator prevents a short circuit between the wire and the metal
sheath.
• Inconel, a nickel-iron chromium alloy, is normally used in manufacturing the
RTD sheath because of its inherent corrosion resistance.
• When placed in a liquid or gas medium, the Inconel sheath quickly reaches the
temperature of the medium. The change in temperature will cause the platinum
wire to heat or cool, resulting in a proportional change in resistance.
Resistance Temperature Detectors (RTDs)
12-07-2020 9
 Advantages:
• Linear resistance with temperature, good stability, wide range of operating
temperature, interchangeable over wide temperature range.
 Disadvantages:
• Small resistance changes with temperature, responses may be slower, subject
to self-heating, transmitter or three to four wire leads required for lead
resistance compensation, external circuit power required.
Thermistors
12-07-2020 10
 Thermistors are temperature sensitive semiconductors that exhibit a large
change in resistance over a relatively small range of temperature.
 There are two main types of thermistors: positive temperature coefficient
(PTC) and negative temperature coefficient (NTC).
 NTC thermistors exhibit the characteristic of resistance falling with increasing
temperature. These are most commonly used for temperature measurement.
Thermistors Materials & Construction
12-07-2020 11
 A thermistor is similar to an RTD, but a semiconductor material is used
instead of a metal.
 A thermistor is a solid-state device and has larger sensitivity than does an
RTD. Unlike RTD's, the temperature-resistance characteristic of a thermistor
is non-linear, and cannot be characterized by a single coefficient.
 Thermistors cannot be used to measure high temperatures compared to RTDs.
In fact, the maximum temperature of operation is sometimes only 100 or
200°C.
12-07-2020 12
• From the circuit diagram, it is clear that this is a simple voltage divider. Rs is some fixed
(supply) resistor. Rs and the supply voltage, Vs, can be adjusted to obtain the desired
range of output voltage Vo for a given range of temperature.
 Advantages:
• Large resistance changes with temperature, rapid response time, good stability, high
resistance eliminates difficulties caused by lead resistance, low cost and interchangeable.
 Disadvantages:
• Non-linear, limited operating temperature range, may be subjected to inaccuracy due to
overheating, current source required.
Thermocouples
12-07-2020 13
 Thermocouple Construction
• A thermocouple is constructed of two dissimilar metal wires joined at one end.
When one end of each wire is connected to a measuring instrument, the
thermocouple becomes a sensitive and highly accurate measuring device.
• Thermocouples may be constructed of several different combinations of
materials.
• The performance of a thermocouple material is generally determined by using
that material with platinum.
• The most important factor to be considered when selecting a pair of materials is
the "thermoelectric difference" between the two materials.
• A significant difference between the two materials will result in better
thermocouple performance.
12-07-2020 14
 Figure shows the internal construction of a typical
thermocouple. The leads of the thermocouple are
encased in a rigid metal sheath.
 The measuring junction is normally formed at the
bottom of the thermocouple housing.
 Magnesium oxide surrounds the thermocouple wires
to prevent vibration that could damage the fine wires
and to enhance heat transfer between the measuring
junction and the medium surrounding the
thermocouple.
12-07-2020 15
 Thermocouple Operation
 Thermocouples will cause an electric current to
flow in the attached circuit when subjected to
changes in temperature.
 The amount of current that will be produced is
dependent on the temperature difference between
the measurement and reference junction; the
characteristics of the two metals used; and the
characteristics of the attached circuit.
12-07-2020 16
 Heating the measuring junction of thermocouple produces a voltage which is greater
than the voltage across the reference junction.
 The difference between the two voltages is proportional to the difference in temperature
and can be measured on the voltmeter (in millivolts).
 For ease of operator use, some voltmeters are set up to read out directly in temperature
through use of electronic circuity.
Bellows-Type Detectors
12-07-2020 17
 The need for a pressure sensing element that was extremely sensitive to low
pressures and provided power for activating recording and indicating
mechanisms resulted in the development of the metallic bellows pressure
sensing element.
 The metallic bellows is most accurate when measuring pressures from 0.5 to 75
psi. However, when used in conjunction with a heavy range spring, some
bellows can be used to measure pressures of over 1000 psi. Figure shows a
basic metallic bellows pressure sensing element.
12-07-2020 18
 Bellows-Type Pressure Detector Operation
• The bellows is a one-piece, collapsible, seamless metallic
unit that has deep folds formed from very thin-walled
tubing.
• The diameter of the bellows ranges from 0.5 to 12 in. and
may have as many as 24 folds.
• System pressure is applied to the internal volume of the
bellows.
• The moving end of the bellows is connected to a
mechanical linkage assembly.
• As the bellows and linkage assembly moves, either an
electrical signal is generated or a direct pressure indication
is provided.
• The flexibility of a metallic bellows is similar in character
to that of a helical, coiled compression spring. Up to the
elastic limit of the bellows, the relation between
increments of load and deflection is linear.
12-07-2020 19
• This relationship exists only when the bellows is under compression. It is necessary to
construct the bellows such that all of the travel occurs on the compression side of the
point of equilibrium.
• Therefore, in practice, the bellows must always be opposed by a spring, and the
deflection characteristics will be the resulting force of the spring and bellows.
 Advantages
• Its cost is moderate.
• It is able to deliver high force.
• It is adaptable for absolute and differential pressures.
• It is good to low-to moderate range.
 Disadvantages
• It needs ambient temperature compensation.
• It is unsuitable for high pressures.
• The availability of construction metals is limited.
Bourdon Tube-Type Detectors
12-07-2020 20
 Working Principle
• The Bourdon pressure gauge uses the principle that a flattened tube tends to
straighten or regain its circular form in cross-section when pressurized.
•
• This change in cross-section may be hardly noticeable, involving moderate
stresses within the elastic range of easily workable materials.
• The strain of the material of the tube is magnified by forming the tube into a C
shape or even a helix, such that the entire tube tends to straighten out or uncoil
elastically as it is pressurized.
12-07-2020 21
 Bourdon Tube-Type Detectors Operation
• It consists of a thin-walled tube that is flattened diametrically on opposite sides to
produce a cross-sectional area elliptical in shape, having two long flat sides and two
short round sides.
• Pressure applied to the inside of the tube causes distention of the flat sections and tends
to restore its original round cross-section.
• This change in cross-section causes the tube to straighten slightly.
12-07-2020 22
• Tube is permanently fastened at one end, the tip of the tube traces a curve that is the
result of the change in angular position with respect to the center.
• Within limits, the movement of the tip of the tube can then be used to position a pointer
or to develop an equivalent electrical signal to indicate the value of the applied internal
pressure.
 Advantages of Bourdon Gauges
• Inexpensive
• Simple Design
• Good accuracy except at low pressure. (High-pressure range)
• It can be easily used with electrical devices
 Disadvantages of Bourdon Gauges
• Susceptible to shock and vibration
• Gauges are subjected to hysteresis
Float Sensor
12-07-2020 23
 Principle of Operation
• A liquid level control system by using a float sensor works on the principle of
buoyancy, which states, “A float immersed in a liquid is buoyed towards upward
direction by an applied equal force to the weight of the displaced liquid”.
• As a result, the body drives partially and gets submerged upon the liquid surface
and covers the same distance the liquid level moves.
12-07-2020 24
 Construction
• A level measurement float system consists of a float, a sensor stem, a magnet, a reed
switch and a weight suspended on the outside of the open tank.
• A scale is fixed on the outside of the tank, and the contents of the tank’s level are
indicated by the position of the weight along the scale.
 Working
• Level detection of liquids is often done with a float-type liquid level switch.
• The float transfers on a mechanical arm or sliding pole and activates a switch when the
level moves towards upward direction.
• Sometimes the float itself contains a small magnet that varies the state of a switch when
the liquid level gets moving up and moves into the original position.
• This type of level sensor comes with many advantages like it is very simple, highly
accurate, and best suitable for various products.
12-07-2020 25
 The Disadvantages of this sensor are that it requires various mechanical equipment,
especially the pressure vessels.
 Float Sensor Application
• In view of the requirements pertaining to the increase in usage of sealed tanks, the
current industrial systems make use of this type of float method for precise reading and
accuracy,
• It is a good example of electronics and mechanical engineering, making it the most
accurate level-measuring system for various applications in very large storage tanks.
Ultrasonic Sensor
12-07-2020 26
 A continuous level sensor is most sophisticated and also provides liquid level
monitoring of an entire system.
 This liquid level sensor is used to measure the fluid level within a specified
range, moderately than at a one point, which produces an analogue output and
directly correlates to the level in the vessel.
 To create a liquid level management system, the output signal is
interconnected to process a control loop and linked as a visual liquid level
indicator.
Ultrasonic Sensor
12-07-2020 27
 Principle of Operation
• Ultrasonic level instruments work on the basic time-of-flight principle which
states that sending a sound wave from a peizo electric transducer to the contents
of the vessel, which may contain liquid, solid or slurries level.
12-07-2020 28
 Construction and Working
• This liquid level sensor comprises two elements such as an associated
electronic transceiver and a transducer with relatively high efficiency.
• In case of a liquid level controller, the fluid level can be determined by
measuring the trip time difference between a transmitted ultrasonic pulse and
a reflected echo.
• The frequency range for ultrasonic methods varies from a range of 15-200
kHz for transmitting and receiving ultrasonic waves.
12-07-2020 29
 Advantage
• The ultrasonic sensors are advantageous as they are not in direct contact with
the product, and the level measurement is done without involving any
physical contact.
• They do not have any moving parts.
 Disadvantage
• As a disadvantage, these types of sensors are not suitable for higher pressures
in a vacuum and temperature limits of up to 170 degree centigrade.
Magnetic Flow Meter
12-07-2020 30
 Working Principle
• Magnetic Flow Meter Construction are the first type of flowmeters to be
considered for high corrosive applications and for applications involving
measurement of erosive slurries.
• These meters work on the principle of Faraday’s law of electromagnetic
induction, which states that whenever a conductor moves through a magnetic
field of given field strength, a voltage is induced in the conductor proportional
to the relative velocity between the conductor and the magnetic field.
• In case of flowmeters, electrically conductive flowing liquids work as the
other conductor.
12-07-2020 31
 The induced voltage is given by the equation.
where
E= Induced voltage in volts
C = Dimensional constants
B =Magnetic flux in Wb/sq.m
L= Length of the conductor (fluid) in m
V = Velocity of the conductor (fluid) in m/s
12-07-2020 32
 Construction
• The Magnetic Flow Meter Construction consists of an electrically
insulated or non-conducting pipe, such as fibre glass.
• Pair of electrodes mounted opposite each other and flush with the inside
walls of the pipe.
• The magnetic coil mounted around the pipe so that a magnetic field is
generated in a plane mutually perpendicular to the axis of the flow
meter body and to the plane of the electrodes.
• If a metal pipe is used, an electrically insulating liner is provided on the
inside of the pipe.
12-07-2020 33
• The basic operating principle of a Magnetic Flow Meter
Construction in which the flowing liquid acts as a conductor is
shown in Figure.
• A modern design of Magnetic Flow Meter Construction is one
which can be inserted into the line through couplings.
• It consists of electrodes mounted on each side of a probe and
magnetic coils which are also integral to the probe.
• The probe can be mounted on pipes of diameters 152.4 mm and
above can easily be mounted for open channel flow.
12-07-2020 34
Advantages
 It is relatively expensive.
 It works only with fluids which are
adequate electrical conductors.
 It is relatively heavy, especially in
larger sizes.
 It must be full at all times.
• It must be explosion proof when
installed in hazardous electrical
areas.
Disadvantage
 It can handle slurries and greasy
materials.
 It can handle corrosive fluids.
 It has very low pressure drop.
 It is totally obstruction less.
 It is available in large pipe sizes
and capacity as well as in several
construction materials.
 It is capable of handling low flows
Ultrasonic Flow Meter
12-07-2020 35
 An ultrasonic flow meter can be defined as, a meter that is used to
measure liquid velocity with ultrasound to analyse the volume of liquid
flow.
 This is a volumetric flow meter that needs bubble or minute particles
within the liquid flow.
 These meters are suitable in the applications of wastewater but they will
not work with drinking/ distilled water.
 This type of flow meter is ideal for the applications wherever chemical
compatibility, low maintenance, and low-pressure drop are required.
12-07-2020 36
 Working Principle and Construction
• An ultrasonic flow meter construction can be done by using
upstream and downstream transducers, sensor pipe and reflector.
• The working principle of ultrasonic flow meter is, it uses sound
waves to resolve the velocity of a liquid within a pipe.
• In the first condition, the frequencies of ultrasonic waves are
transmitted into a pipe & its indication from the fluid are similar.
• In the second condition, the reflected wave’s frequency is dissimilar
because of the Doppler Effect.
12-07-2020 37
• Whenever the liquid flows in the pipe quickly, then the frequency
shift can be increased linearly.
• The transmitter processes the signals from the wave & its reflections
determine the flow rate.
• The times of the upstream & downstream processed by the
transmitter to decide the flow rate.
12-07-2020 38
Advantages
 It does not block the path of liquid flow.
 The flow of liquid is bidirectional
 The dynamic response of this meter is good.
 The output of this meter is in analog form
 Conservation of energy
 It is handy to fit and maintain
 Versatility is good
 There is no contact to liquid
 There is no leakage risk
 There are no moving parts, pressure loss
 High accuracy
Disadvantage
 It is expensive as compared with other
mechanical flow meters.
 Design of this meter is complex
 Auditory parts of this meter are expensive.
 These meters are complicated as compared
with other meters; it requires specialists for
maintaining and repairing these meters
 It cannot measure cement or concrete pipes
one they rusted.
 It doesn’t work once the pipe contains holes
or bubbles in it
12-07-2020 39
 Applications
• These meters are used in wastewater and dirty liquid applications
• These meters are used wherever chemical compatibility, less maintenance, and low-
pressure drop are required.
• These meters are used to measure the velocity of a liquid through ultrasound to
analyze volume flow.
• These meters measure the disparity between the transit time of ultrasonic pulses
which transmits with the direction of liquid flow
• The applications of these meters range from process to custody flow
• This is one kind of device for volumetric flow measurement for liquids as well as
gases.
• These are excellent alternatives for both vortex & electromagnetic flowmeters.
12-07-2020 40

More Related Content

What's hot

Temprature sensors
Temprature sensorsTemprature sensors
Temprature sensorsSole Michael
 
2015 Temperature Sensors Forecast
2015 Temperature Sensors Forecast2015 Temperature Sensors Forecast
2015 Temperature Sensors Forecasttempalert
 
Transducer-Temperature Measuring Transducers
Transducer-Temperature Measuring Transducers Transducer-Temperature Measuring Transducers
Transducer-Temperature Measuring Transducers Jabir Ali Siddique
 
Temperature Sensors
Temperature SensorsTemperature Sensors
Temperature Sensorssemihdogan
 
Temperature Sensors
Temperature SensorsTemperature Sensors
Temperature Sensorsguest94f9a4
 
Temperature Measuring Seonsors
Temperature Measuring SeonsorsTemperature Measuring Seonsors
Temperature Measuring SeonsorsZaeem Naqvi
 
Temperature measurement
Temperature measurementTemperature measurement
Temperature measurementbkdevaraj
 
Chapter temperature measurement
Chapter  temperature measurementChapter  temperature measurement
Chapter temperature measurementNaman Dave
 
Mechanical temperature measuring devices and their applications
Mechanical temperature measuring devices and their applicationsMechanical temperature measuring devices and their applications
Mechanical temperature measuring devices and their applicationsAnand Prithviraj
 
Automotive Temperature sensors
Automotive Temperature sensorsAutomotive Temperature sensors
Automotive Temperature sensorsHardik Rathod
 
Seminar report on Temperature Measuring Devices
Seminar report on Temperature Measuring DevicesSeminar report on Temperature Measuring Devices
Seminar report on Temperature Measuring DevicesAmbrish Rai
 
Basics of Temperature Measurement
Basics of Temperature MeasurementBasics of Temperature Measurement
Basics of Temperature MeasurementMithila6190
 
Bimetallic strip thermometer
Bimetallic strip thermometerBimetallic strip thermometer
Bimetallic strip thermometerlihoi
 
Limiting Inrush Current with NTC and PTC Thermistors
Limiting Inrush Current with NTC and PTC Thermistors Limiting Inrush Current with NTC and PTC Thermistors
Limiting Inrush Current with NTC and PTC Thermistors Ametherm
 
presentation slide
 presentation slide presentation slide
presentation slideSmit Javiya
 

What's hot (20)

Temprature sensors
Temprature sensorsTemprature sensors
Temprature sensors
 
2015 Temperature Sensors Forecast
2015 Temperature Sensors Forecast2015 Temperature Sensors Forecast
2015 Temperature Sensors Forecast
 
What is RTD
What is RTD What is RTD
What is RTD
 
Transducer-Temperature Measuring Transducers
Transducer-Temperature Measuring Transducers Transducer-Temperature Measuring Transducers
Transducer-Temperature Measuring Transducers
 
Temperature Sensors
Temperature SensorsTemperature Sensors
Temperature Sensors
 
Temperature measurement
Temperature measurementTemperature measurement
Temperature measurement
 
Temperature Sensors
Temperature SensorsTemperature Sensors
Temperature Sensors
 
Temperature Measuring Seonsors
Temperature Measuring SeonsorsTemperature Measuring Seonsors
Temperature Measuring Seonsors
 
Temperature sensor
Temperature sensorTemperature sensor
Temperature sensor
 
Temperature measurement
Temperature measurementTemperature measurement
Temperature measurement
 
Chapter temperature measurement
Chapter  temperature measurementChapter  temperature measurement
Chapter temperature measurement
 
Thermocouples sensors
Thermocouples sensorsThermocouples sensors
Thermocouples sensors
 
Mechanical temperature measuring devices and their applications
Mechanical temperature measuring devices and their applicationsMechanical temperature measuring devices and their applications
Mechanical temperature measuring devices and their applications
 
Automotive Temperature sensors
Automotive Temperature sensorsAutomotive Temperature sensors
Automotive Temperature sensors
 
Seminar report on Temperature Measuring Devices
Seminar report on Temperature Measuring DevicesSeminar report on Temperature Measuring Devices
Seminar report on Temperature Measuring Devices
 
Basics of Temperature Measurement
Basics of Temperature MeasurementBasics of Temperature Measurement
Basics of Temperature Measurement
 
strain gauges
strain gauges strain gauges
strain gauges
 
Bimetallic strip thermometer
Bimetallic strip thermometerBimetallic strip thermometer
Bimetallic strip thermometer
 
Limiting Inrush Current with NTC and PTC Thermistors
Limiting Inrush Current with NTC and PTC Thermistors Limiting Inrush Current with NTC and PTC Thermistors
Limiting Inrush Current with NTC and PTC Thermistors
 
presentation slide
 presentation slide presentation slide
presentation slide
 

Similar to Indicating, recording & controlling devices used in dairy plants principle, working mechanisms & applications

Introduction to rtd and thermocouple by yogesh k. kirange
Introduction to rtd and thermocouple by yogesh k. kirangeIntroduction to rtd and thermocouple by yogesh k. kirange
Introduction to rtd and thermocouple by yogesh k. kirangeYogesh Kirange
 
Thermocouple and RTD.pptx
Thermocouple and RTD.pptxThermocouple and RTD.pptx
Thermocouple and RTD.pptxYashGarale1
 
Electrical temperature measurement
Electrical temperature measurementElectrical temperature measurement
Electrical temperature measurementRonak Parmar
 
TEMPERATURE SENSORS.pptx
TEMPERATURE SENSORS.pptxTEMPERATURE SENSORS.pptx
TEMPERATURE SENSORS.pptxshadrickkasuba
 
Introduction to transducers
Introduction to transducersIntroduction to transducers
Introduction to transducersYogesh Kirange
 
Developing an experimental set up for measurement of cutting temperature in T...
Developing an experimental set up for measurement of cutting temperature in T...Developing an experimental set up for measurement of cutting temperature in T...
Developing an experimental set up for measurement of cutting temperature in T...HIMANSHU KUMAR SINGH
 
A presentation on transducerpptx
A presentation on transducerpptxA presentation on transducerpptx
A presentation on transducerpptxAl Nabil
 
Temperature Measuring Seonsors
Temperature Measuring SeonsorsTemperature Measuring Seonsors
Temperature Measuring SeonsorsZaeem Naqvi
 
Temperature measurement part II
Temperature measurement   part IITemperature measurement   part II
Temperature measurement part IIBurdwan University
 
Temperature Sensor Thermocouple and RTD
Temperature Sensor Thermocouple and RTDTemperature Sensor Thermocouple and RTD
Temperature Sensor Thermocouple and RTDrashid09
 
ResistanceTemperatureThermometer_RTD.ppt
ResistanceTemperatureThermometer_RTD.pptResistanceTemperatureThermometer_RTD.ppt
ResistanceTemperatureThermometer_RTD.pptDivya392513
 

Similar to Indicating, recording & controlling devices used in dairy plants principle, working mechanisms & applications (20)

Introduction to rtd and thermocouple by yogesh k. kirange
Introduction to rtd and thermocouple by yogesh k. kirangeIntroduction to rtd and thermocouple by yogesh k. kirange
Introduction to rtd and thermocouple by yogesh k. kirange
 
RTD.ppt
RTD.pptRTD.ppt
RTD.ppt
 
Thermocouple and RTD.pptx
Thermocouple and RTD.pptxThermocouple and RTD.pptx
Thermocouple and RTD.pptx
 
Electrical temperature measurement
Electrical temperature measurementElectrical temperature measurement
Electrical temperature measurement
 
Industrial Temperature Measurement
Industrial Temperature MeasurementIndustrial Temperature Measurement
Industrial Temperature Measurement
 
Transducers
TransducersTransducers
Transducers
 
Temperature Sensors
Temperature SensorsTemperature Sensors
Temperature Sensors
 
TEMPERATURE SENSORS.pptx
TEMPERATURE SENSORS.pptxTEMPERATURE SENSORS.pptx
TEMPERATURE SENSORS.pptx
 
TEMPRATURE MEASUREMENT INSTRUMENTS
TEMPRATURE MEASUREMENT INSTRUMENTSTEMPRATURE MEASUREMENT INSTRUMENTS
TEMPRATURE MEASUREMENT INSTRUMENTS
 
Introduction to transducers
Introduction to transducersIntroduction to transducers
Introduction to transducers
 
Developing an experimental set up for measurement of cutting temperature in T...
Developing an experimental set up for measurement of cutting temperature in T...Developing an experimental set up for measurement of cutting temperature in T...
Developing an experimental set up for measurement of cutting temperature in T...
 
FINAL PPT.pptx
FINAL PPT.pptxFINAL PPT.pptx
FINAL PPT.pptx
 
A presentation on transducerpptx
A presentation on transducerpptxA presentation on transducerpptx
A presentation on transducerpptx
 
Temperature Measuring Seonsors
Temperature Measuring SeonsorsTemperature Measuring Seonsors
Temperature Measuring Seonsors
 
Temperature measurement part II
Temperature measurement   part IITemperature measurement   part II
Temperature measurement part II
 
Temperature Sensor Thermocouple and RTD
Temperature Sensor Thermocouple and RTDTemperature Sensor Thermocouple and RTD
Temperature Sensor Thermocouple and RTD
 
Temperature Measurements
Temperature MeasurementsTemperature Measurements
Temperature Measurements
 
Rtd
RtdRtd
Rtd
 
ResistanceTemperatureThermometer_RTD.ppt
ResistanceTemperatureThermometer_RTD.pptResistanceTemperatureThermometer_RTD.ppt
ResistanceTemperatureThermometer_RTD.ppt
 
Rtd and thermocouples
Rtd and thermocouplesRtd and thermocouples
Rtd and thermocouples
 

Indicating, recording & controlling devices used in dairy plants principle, working mechanisms & applications

  • 1. Indicating, Recording & Controlling Devices Used in Dairy Plants Principle, Working Mechanisms & Applications Subject : Instrumentation & Process Control (DE-525) Submitted by : Dhruv Beladiya M.Tech ( 2nd Semester ) Department of Dairy Engineering
  • 2. CONTENTS Introduction Resistance Temperature Detectors (RTDs) Effect of Temperature on Sorption Isotherm Measurement of Sorption Isotherm Bellows-Type Pressure Detectors Thermistors Thermocouples Bourdon Tube-Type Pressure Detectors Level Indicator - Float Sensor Level Indicator - Ultrasonic Sensor Magnetic Flow Meter Ultrasonic Flow Meter Conclusion 12-07-2020 2
  • 3. INTRODUCTION 12-07-2020 3 • The most important properties of dairy processes subject to measurement that reflect both process operation and product quality are classified as objective or subjective. • Examples of the former are pH, temperature, flow rates, pressure, level, etc. • Sensors for on-line measurement of such properties have been available already for a long time. • Properties such as taste, flavour, colour and consistency are considered as subjective and difficult to measure. • Commercial sensors applied in the dairy industry are subject to several quality constraints such as sanitary, safety and environmental requirements.
  • 4. CONT. 12-07-2020 4 • A trend in the new sensor design technologies is the increasing integration of the sensing elements into silicon chip microcircuits. • These new measurement devices directly incorporate all circuitry needed to self- compensate for environmental changes and yield an output that is suitably amplified for transmission to standard electronic controllers. • These sensors offer the advantage of small size, reduced prices and practically no mechanical parts to wear out.
  • 5. Resistance Temperature Detectors (RTDs) 12-07-2020 5 • A resistance temperature detector (abbreviated RTD) is basically either a long, small diameter metal wire wound in a coil or an etched grid on a substrate, much like a strain gage. • Platinum is the most common metal used for RTDs.
  • 6. 12-07-2020 6  Principle of Operation • Resistance Temperature Detectors (RTD) operates on the principle that the electrical resistance of a metal changes predictably in an essentially linear and repeatable manner with changes in temperature. • RTD have a positive temperature coefficient (resistance increases with temperature). • The resistance of the element at a base temperature is proportional to the length of the element and the inverse of the cross-sectional area. • A typical electrical circuit designed to measure temperature with RTDs actually measures a change in resistance of the RTD, which is then used to calculate a change in temperature. • The resistance of an RTD increases with increasing temperature, just as the resistance of a strain gage increases with increasing strain.
  • 7. 12-07-2020 7  RTD Materials & Construction • RTD acts somewhat like an electrical transducer, converting changes in temperature to voltage signals by the measurement of resistance. • The metals that are best suited for use as RTD sensors are pure metals or certain alloys of uniform quality that increase in resistance as temperature increases and conversely decrease in resistance as temperature decreases. • Only a few metals have the properties necessary for use in RTD elements. Common materials used in RTD sensor are BALCO wire, Copper, Platinum.
  • 8. 12-07-2020 8 • This particular design has a platinum element that is surrounded by a porcelain insulator. The insulator prevents a short circuit between the wire and the metal sheath. • Inconel, a nickel-iron chromium alloy, is normally used in manufacturing the RTD sheath because of its inherent corrosion resistance. • When placed in a liquid or gas medium, the Inconel sheath quickly reaches the temperature of the medium. The change in temperature will cause the platinum wire to heat or cool, resulting in a proportional change in resistance.
  • 9. Resistance Temperature Detectors (RTDs) 12-07-2020 9  Advantages: • Linear resistance with temperature, good stability, wide range of operating temperature, interchangeable over wide temperature range.  Disadvantages: • Small resistance changes with temperature, responses may be slower, subject to self-heating, transmitter or three to four wire leads required for lead resistance compensation, external circuit power required.
  • 10. Thermistors 12-07-2020 10  Thermistors are temperature sensitive semiconductors that exhibit a large change in resistance over a relatively small range of temperature.  There are two main types of thermistors: positive temperature coefficient (PTC) and negative temperature coefficient (NTC).  NTC thermistors exhibit the characteristic of resistance falling with increasing temperature. These are most commonly used for temperature measurement.
  • 11. Thermistors Materials & Construction 12-07-2020 11  A thermistor is similar to an RTD, but a semiconductor material is used instead of a metal.  A thermistor is a solid-state device and has larger sensitivity than does an RTD. Unlike RTD's, the temperature-resistance characteristic of a thermistor is non-linear, and cannot be characterized by a single coefficient.  Thermistors cannot be used to measure high temperatures compared to RTDs. In fact, the maximum temperature of operation is sometimes only 100 or 200°C.
  • 12. 12-07-2020 12 • From the circuit diagram, it is clear that this is a simple voltage divider. Rs is some fixed (supply) resistor. Rs and the supply voltage, Vs, can be adjusted to obtain the desired range of output voltage Vo for a given range of temperature.  Advantages: • Large resistance changes with temperature, rapid response time, good stability, high resistance eliminates difficulties caused by lead resistance, low cost and interchangeable.  Disadvantages: • Non-linear, limited operating temperature range, may be subjected to inaccuracy due to overheating, current source required.
  • 13. Thermocouples 12-07-2020 13  Thermocouple Construction • A thermocouple is constructed of two dissimilar metal wires joined at one end. When one end of each wire is connected to a measuring instrument, the thermocouple becomes a sensitive and highly accurate measuring device. • Thermocouples may be constructed of several different combinations of materials. • The performance of a thermocouple material is generally determined by using that material with platinum. • The most important factor to be considered when selecting a pair of materials is the "thermoelectric difference" between the two materials. • A significant difference between the two materials will result in better thermocouple performance.
  • 14. 12-07-2020 14  Figure shows the internal construction of a typical thermocouple. The leads of the thermocouple are encased in a rigid metal sheath.  The measuring junction is normally formed at the bottom of the thermocouple housing.  Magnesium oxide surrounds the thermocouple wires to prevent vibration that could damage the fine wires and to enhance heat transfer between the measuring junction and the medium surrounding the thermocouple.
  • 15. 12-07-2020 15  Thermocouple Operation  Thermocouples will cause an electric current to flow in the attached circuit when subjected to changes in temperature.  The amount of current that will be produced is dependent on the temperature difference between the measurement and reference junction; the characteristics of the two metals used; and the characteristics of the attached circuit.
  • 16. 12-07-2020 16  Heating the measuring junction of thermocouple produces a voltage which is greater than the voltage across the reference junction.  The difference between the two voltages is proportional to the difference in temperature and can be measured on the voltmeter (in millivolts).  For ease of operator use, some voltmeters are set up to read out directly in temperature through use of electronic circuity.
  • 17. Bellows-Type Detectors 12-07-2020 17  The need for a pressure sensing element that was extremely sensitive to low pressures and provided power for activating recording and indicating mechanisms resulted in the development of the metallic bellows pressure sensing element.  The metallic bellows is most accurate when measuring pressures from 0.5 to 75 psi. However, when used in conjunction with a heavy range spring, some bellows can be used to measure pressures of over 1000 psi. Figure shows a basic metallic bellows pressure sensing element.
  • 18. 12-07-2020 18  Bellows-Type Pressure Detector Operation • The bellows is a one-piece, collapsible, seamless metallic unit that has deep folds formed from very thin-walled tubing. • The diameter of the bellows ranges from 0.5 to 12 in. and may have as many as 24 folds. • System pressure is applied to the internal volume of the bellows. • The moving end of the bellows is connected to a mechanical linkage assembly. • As the bellows and linkage assembly moves, either an electrical signal is generated or a direct pressure indication is provided. • The flexibility of a metallic bellows is similar in character to that of a helical, coiled compression spring. Up to the elastic limit of the bellows, the relation between increments of load and deflection is linear.
  • 19. 12-07-2020 19 • This relationship exists only when the bellows is under compression. It is necessary to construct the bellows such that all of the travel occurs on the compression side of the point of equilibrium. • Therefore, in practice, the bellows must always be opposed by a spring, and the deflection characteristics will be the resulting force of the spring and bellows.  Advantages • Its cost is moderate. • It is able to deliver high force. • It is adaptable for absolute and differential pressures. • It is good to low-to moderate range.  Disadvantages • It needs ambient temperature compensation. • It is unsuitable for high pressures. • The availability of construction metals is limited.
  • 20. Bourdon Tube-Type Detectors 12-07-2020 20  Working Principle • The Bourdon pressure gauge uses the principle that a flattened tube tends to straighten or regain its circular form in cross-section when pressurized. • • This change in cross-section may be hardly noticeable, involving moderate stresses within the elastic range of easily workable materials. • The strain of the material of the tube is magnified by forming the tube into a C shape or even a helix, such that the entire tube tends to straighten out or uncoil elastically as it is pressurized.
  • 21. 12-07-2020 21  Bourdon Tube-Type Detectors Operation • It consists of a thin-walled tube that is flattened diametrically on opposite sides to produce a cross-sectional area elliptical in shape, having two long flat sides and two short round sides. • Pressure applied to the inside of the tube causes distention of the flat sections and tends to restore its original round cross-section. • This change in cross-section causes the tube to straighten slightly.
  • 22. 12-07-2020 22 • Tube is permanently fastened at one end, the tip of the tube traces a curve that is the result of the change in angular position with respect to the center. • Within limits, the movement of the tip of the tube can then be used to position a pointer or to develop an equivalent electrical signal to indicate the value of the applied internal pressure.  Advantages of Bourdon Gauges • Inexpensive • Simple Design • Good accuracy except at low pressure. (High-pressure range) • It can be easily used with electrical devices  Disadvantages of Bourdon Gauges • Susceptible to shock and vibration • Gauges are subjected to hysteresis
  • 23. Float Sensor 12-07-2020 23  Principle of Operation • A liquid level control system by using a float sensor works on the principle of buoyancy, which states, “A float immersed in a liquid is buoyed towards upward direction by an applied equal force to the weight of the displaced liquid”. • As a result, the body drives partially and gets submerged upon the liquid surface and covers the same distance the liquid level moves.
  • 24. 12-07-2020 24  Construction • A level measurement float system consists of a float, a sensor stem, a magnet, a reed switch and a weight suspended on the outside of the open tank. • A scale is fixed on the outside of the tank, and the contents of the tank’s level are indicated by the position of the weight along the scale.  Working • Level detection of liquids is often done with a float-type liquid level switch. • The float transfers on a mechanical arm or sliding pole and activates a switch when the level moves towards upward direction. • Sometimes the float itself contains a small magnet that varies the state of a switch when the liquid level gets moving up and moves into the original position. • This type of level sensor comes with many advantages like it is very simple, highly accurate, and best suitable for various products.
  • 25. 12-07-2020 25  The Disadvantages of this sensor are that it requires various mechanical equipment, especially the pressure vessels.  Float Sensor Application • In view of the requirements pertaining to the increase in usage of sealed tanks, the current industrial systems make use of this type of float method for precise reading and accuracy, • It is a good example of electronics and mechanical engineering, making it the most accurate level-measuring system for various applications in very large storage tanks.
  • 26. Ultrasonic Sensor 12-07-2020 26  A continuous level sensor is most sophisticated and also provides liquid level monitoring of an entire system.  This liquid level sensor is used to measure the fluid level within a specified range, moderately than at a one point, which produces an analogue output and directly correlates to the level in the vessel.  To create a liquid level management system, the output signal is interconnected to process a control loop and linked as a visual liquid level indicator.
  • 27. Ultrasonic Sensor 12-07-2020 27  Principle of Operation • Ultrasonic level instruments work on the basic time-of-flight principle which states that sending a sound wave from a peizo electric transducer to the contents of the vessel, which may contain liquid, solid or slurries level.
  • 28. 12-07-2020 28  Construction and Working • This liquid level sensor comprises two elements such as an associated electronic transceiver and a transducer with relatively high efficiency. • In case of a liquid level controller, the fluid level can be determined by measuring the trip time difference between a transmitted ultrasonic pulse and a reflected echo. • The frequency range for ultrasonic methods varies from a range of 15-200 kHz for transmitting and receiving ultrasonic waves.
  • 29. 12-07-2020 29  Advantage • The ultrasonic sensors are advantageous as they are not in direct contact with the product, and the level measurement is done without involving any physical contact. • They do not have any moving parts.  Disadvantage • As a disadvantage, these types of sensors are not suitable for higher pressures in a vacuum and temperature limits of up to 170 degree centigrade.
  • 30. Magnetic Flow Meter 12-07-2020 30  Working Principle • Magnetic Flow Meter Construction are the first type of flowmeters to be considered for high corrosive applications and for applications involving measurement of erosive slurries. • These meters work on the principle of Faraday’s law of electromagnetic induction, which states that whenever a conductor moves through a magnetic field of given field strength, a voltage is induced in the conductor proportional to the relative velocity between the conductor and the magnetic field. • In case of flowmeters, electrically conductive flowing liquids work as the other conductor.
  • 31. 12-07-2020 31  The induced voltage is given by the equation. where E= Induced voltage in volts C = Dimensional constants B =Magnetic flux in Wb/sq.m L= Length of the conductor (fluid) in m V = Velocity of the conductor (fluid) in m/s
  • 32. 12-07-2020 32  Construction • The Magnetic Flow Meter Construction consists of an electrically insulated or non-conducting pipe, such as fibre glass. • Pair of electrodes mounted opposite each other and flush with the inside walls of the pipe. • The magnetic coil mounted around the pipe so that a magnetic field is generated in a plane mutually perpendicular to the axis of the flow meter body and to the plane of the electrodes. • If a metal pipe is used, an electrically insulating liner is provided on the inside of the pipe.
  • 33. 12-07-2020 33 • The basic operating principle of a Magnetic Flow Meter Construction in which the flowing liquid acts as a conductor is shown in Figure. • A modern design of Magnetic Flow Meter Construction is one which can be inserted into the line through couplings. • It consists of electrodes mounted on each side of a probe and magnetic coils which are also integral to the probe. • The probe can be mounted on pipes of diameters 152.4 mm and above can easily be mounted for open channel flow.
  • 34. 12-07-2020 34 Advantages  It is relatively expensive.  It works only with fluids which are adequate electrical conductors.  It is relatively heavy, especially in larger sizes.  It must be full at all times. • It must be explosion proof when installed in hazardous electrical areas. Disadvantage  It can handle slurries and greasy materials.  It can handle corrosive fluids.  It has very low pressure drop.  It is totally obstruction less.  It is available in large pipe sizes and capacity as well as in several construction materials.  It is capable of handling low flows
  • 35. Ultrasonic Flow Meter 12-07-2020 35  An ultrasonic flow meter can be defined as, a meter that is used to measure liquid velocity with ultrasound to analyse the volume of liquid flow.  This is a volumetric flow meter that needs bubble or minute particles within the liquid flow.  These meters are suitable in the applications of wastewater but they will not work with drinking/ distilled water.  This type of flow meter is ideal for the applications wherever chemical compatibility, low maintenance, and low-pressure drop are required.
  • 36. 12-07-2020 36  Working Principle and Construction • An ultrasonic flow meter construction can be done by using upstream and downstream transducers, sensor pipe and reflector. • The working principle of ultrasonic flow meter is, it uses sound waves to resolve the velocity of a liquid within a pipe. • In the first condition, the frequencies of ultrasonic waves are transmitted into a pipe & its indication from the fluid are similar. • In the second condition, the reflected wave’s frequency is dissimilar because of the Doppler Effect.
  • 37. 12-07-2020 37 • Whenever the liquid flows in the pipe quickly, then the frequency shift can be increased linearly. • The transmitter processes the signals from the wave & its reflections determine the flow rate. • The times of the upstream & downstream processed by the transmitter to decide the flow rate.
  • 38. 12-07-2020 38 Advantages  It does not block the path of liquid flow.  The flow of liquid is bidirectional  The dynamic response of this meter is good.  The output of this meter is in analog form  Conservation of energy  It is handy to fit and maintain  Versatility is good  There is no contact to liquid  There is no leakage risk  There are no moving parts, pressure loss  High accuracy Disadvantage  It is expensive as compared with other mechanical flow meters.  Design of this meter is complex  Auditory parts of this meter are expensive.  These meters are complicated as compared with other meters; it requires specialists for maintaining and repairing these meters  It cannot measure cement or concrete pipes one they rusted.  It doesn’t work once the pipe contains holes or bubbles in it
  • 39. 12-07-2020 39  Applications • These meters are used in wastewater and dirty liquid applications • These meters are used wherever chemical compatibility, less maintenance, and low- pressure drop are required. • These meters are used to measure the velocity of a liquid through ultrasound to analyze volume flow. • These meters measure the disparity between the transit time of ultrasonic pulses which transmits with the direction of liquid flow • The applications of these meters range from process to custody flow • This is one kind of device for volumetric flow measurement for liquids as well as gases. • These are excellent alternatives for both vortex & electromagnetic flowmeters.