training at hindustan zinc, chittorgarh
DESCRIPTION
CHAPTER 1 INTRODUCTION1.1REQUIREMENT OF PRACTICAL TRANING:Engineering profession is full of practical challenges as every engineer has to confront various problems in his/her professional career. Therefore an engineer must be aware of practical challenges right from the college level. Sometimes it becomes essential to find the solutions to the problems practically, and then comes the need to implement the theoretical knowledge gained during study life into the practical environment. This pTRANSCRIPT
CHAPTER 1
INTRODUCTION
1.1 REQUIREMENT OF PRACTICAL TRANING:
Engineering profession is full of practical challenges as every engineer has to
confront various problems in his/her professional career. Therefore an engineer
must be aware of practical challenges right from the college level. Sometimes
it becomes essential to find the solutions to the problems practically, and then
comes the need to implement the theoretical knowledge gained during study
life into the practical environment.
This practical implementation not only requires thorough knowledge of
the subject but also the skill and real time decision making so that the task can
be performed with full efficiency and accuracy. This skill and decision making
power comes only when one should be aware of the live processing and
working of an industry, therefore every Engineer has to undergo a practical
summer internship in an organization so that he can practically visualize the
working, management, and various techniques of the industry and can simulate
on real machines and gadgets with his own hands.
Therefore Rajasthan Technical University, Kota has prescribed 30 days
practical summer training for every Engineer after the completion of the VIth
Semester to enhance one’s practical approach and also the application of the
theoretical knowledge.
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1.2 ROLE OF INDUSTRIAL AUTOMATION:
Life has become simpler and luxurious after the development of science and
engineering. Everything has become automatic and can be operated by just one
click or one press of a button. This has led to revolution in current scenario. It
has reduced labor and has increased efficiency and accuracy as the tasks
considered too difficult and impossible for human being can now be
accomplished with the help of automatic machines. This requires low
manpower and can save a lot time.
Automation in industries play a major role as everyday, the
requirements are increasing and accordingly the production needs to be
increased to earn maximum profits. Today every production industry rely on
heavy machinery which works automatically and saves both power and
money with least risk to human life. Thus automation is a necessary tool for
the increment in production as well as profit for an organization. Therefore it
is both essential and beneficial to learn the role of automation as it requires
core Electronics & Instrumentation along with Computer applications.
1.3 AUTOMATION AT HZL:
Hindustan Zinc Limited is a world renowned organization producing millions
of tons of Zinc (Zn) and Lead (Pb) every year. It requires a lot of sophisticated
machinery and equipments, costing millions of rupees to produce such a huge
amount of concentrate. Therefore skilled labor and proper conditioning is very
essential. Every task on this level cannot be performed by human being for
such huge quantities with proper accuracy and efficiency in the given time
slot, here comes the role of automation. Each equipment works automatically
under the prescribed measurements and norms with complete human
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supervision. Various sensors, transducers, motors, pumps run automatically
24x7 for zinc and lead production. The working of these equipments is
monitored by Programmable Logic control which fetches each and every
information of equipment connected in the stream. It visualizes the functioning
of the plant on a computer screen which is supervised by an Engineer.
Automation system comes under the supervision of Electronics and
Instrumentation department which is responsible for proper functioning of
Smelters. The company profile and training report is accommodated in
forthcoming chapters.
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CHAPTER 2
ORGANIZATION PROFILE
2.1 HISTORY:
Hindustan Zinc Limited, a Vedanta Group Organization the only integrated
Zinc manufacturer in India and is the world`s second largest and India`s largest
integrated Zinc producer and also one of the lowest cost Zinc producer in the
world, with a global share of 6% in Zinc. The company has four mines & four
smelting operations, captive mines are located at Rampura Agucha (Bhilwara),
Rajpura Dariba (Udaipur), Sindesar Khurd and Zawar (Udaipur) with smelters
at Chanderiya, Debari and Dariba located in Rajasthan & Vizag (Andhra
Pradesh).
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Fig .1 HZL Distributions in India
Chanderiya Smelting Complex is located 110kms from north of
Udaipur in the State of Rajasthan,India.It was commissioned in year 1991 with
an initial production capacity of 70,000 tonnes of per annum Zinc & 35,000
tonnes of Lead per annum.
It is basically the single largest Zinc Smelting Complex in the world.
Now the metal production capacity is 610,000 tonnes per annum.With a talent
pool of over 6400 employees and about 16% women employees in the fresh
intake, HZL is emerging as one of the most preferred employer in the industry.
The company has tried to maintain and upkeep the quality of life of its
employees.
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Fig 2. Chanderiya Lead Zinc Smelter
2.2 EXCELLENCE AT HZL:
You set a vision and you build a road map to achieve it, Hindustan Zinc was
no different, but the most important was the approach to excel- to make
Hindustan Zinc Ltd a world class company that is focused to achieve
excellence and set global benchmark. This is what lies in the working culture
at HZL, and this is best reflected in their mission and vision.
MISSION: Be a world class company, creating value, leveraging mineral
resources and related core competencies.
VISION: To be a global lowest cost Zinc producer, maintaining market
leadership with a million tonne Zinc-Lead metal capacity by 2012 by
innovating, customer oriented and eco-friendly environment and maximizing
stake-holder value.
QUALITY POLICY: Ensure involvement, participation and motivation of
employees and contractor employees in implementation of our environment,
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health and safety management systems through training, awareness and
continual competence building.
2.3 IMPORTANT KEY FEATUERS:
In the past 3 decades, Chanderiya Smelting Complex has continuously made
progress in terms of production, cost and consumer satisfaction, it has made
several milestones in this period. To count a few Key facts are:
1. Annual Production Capacity:
a. Zinc: 525,000 tons per annum
b. Lead: 85,000 tons per annum
c. Silver: 168 tons per annum
2. Products: SHG Zinc & Zinc alloys, PW Zinc, Lead, Silver
2.4 AWARDS AND RECOGNITIONS:
Hindustan Zinc Limited has received various awards in production, consumer
satisfaction, environment, health and safety. Even, it has got various
certifications from government of India and state government. The
organization is been certified by:
1. ISO-9001 (Quality control)
2. ISO-14001 (Environment Management)
3. OHSAS (Occupational health and safety advisory services)
4. SA-8000 (Social accountability)
Besides these major certifications HZL has been recognized by various
prestigious awards in different categories, the few to mention are:
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1. FIMI National Environment award under best open cast mechanized
mine – 2006.
2. Bhilwara Udyog Ratna Award – 2006, 2009.
3. Greentech safety silver award – 2006.
4. “First” overall performance in safety week in Ajmer region – 2006.
5. Golden Peacock Award for environ management – 2009.
6. Ranked second in the top 25 for best employers in India – 2009.
7. 9th Annual Excellence Award in the best manufacturing process – 2008.
8. ROSPA gold award for prevention against accidents – 2008.
9. National energy conservation award – 2008.
10. Gold Pegasus CSR award – 2008.
11. FICCI annual award for Rural and Community development – 2007
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CHAPTER 3
PROCESS
3.1 PYRO PLANT
1. SINTER GROUP
- Sinter Plant
- Acid Plant
- Effuel Treatment Plant
- Tall Gas Treatment
- Reverse Osmosis
2. ZINC CIRCUIT
- Imperial Smelting Furnace/plant
- Zinc Refinery Plant
3. LEAD CIRCUIT
- AUSMELT
- Lead Refinery Plant
- Copper Refinery Plant
- Silver Refinery Plant
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Fig 3 Sinter plant
3.1.1 RAW MATERIAL STOCK YARD WITH LOADING
STATION
Concentrates and fluxes are unloaded from the trucks into grizzly. The
unloading system of belt conveyors takes the material to the respective bay in
the storage yard through a tripper conveyor. The capacities of various
materials and fluxes bay are as follows:
Zinc concentrates (Total) 9450MT
Bulk concentrates 3500MT
Lead concentrates 7500MT
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Limestone fluxes 450MT
Iron fluxes 700MT
From the above storage yard they are carried to proportioning bins by a series
of conveyor system.
3.1.2 CHARGE PROPORTIONING AND CONDITIONING SYSTEM
The raw material can be made to pass through a disintegrator when they
are over size, there are 13 storage bins each having a capacity of 50 cu M, six
bins are for zinc concentrate 3 bins for lead concentrate 1for bulk concentrate
1 for iron flux and 2 for limestone are earmarked in that order lastly, two bins
with capacity of 25 cu M are provided for return fines. All bins are equipped
with vibrator and shock cannons to prevent blockage. Generally, the ratio
between crude charge and return fines will be in ratio of 1:3 to 1:5 in order to
have supplied sulphur of 6% in feed to sinter machine. Plant ventilation dust,
which is removed in a bag filter and stored in a 35 cu M. Bins are being added
to the final stream of charge component entering the mixing drum, moisture
addition is done in a controlled way at mixing and conditioning drums so as to
get a moisture content of 6% in the feed to sinter machine. All the various
sources of input are controlled through weigh feeders located at the bottom of
the proportioning bins.
3.1.3 SINTER MACHINE
The updraft sinter machine has an area of 120 sq m and 109 pallets each
measuring 3m x 1m in size. There are 444 grate bars in a pallet above the
sinter machine, the main and ignition layer bins are located. The ignition layer
thickness is generally adjusted to give 30 mm height and the total layer
thickness maximum is up to 400 mm. The ignition layer is fired by two
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burners operating on L.S.H.S. to get about 1000 C hood temperature. The
ignition gases are drawn by the ignition waste gas fan through the wind box
and conveyed to recalculating gas main. Dust and spillage are removed in a
solid separator. The ignition wind box is equipped with two conveyors, which
are to seal and discharge the sinter machine dust collecting through from the
sinter hood, the rich sulphur dioxide gases are drawn and sent to wet gas
cleaning plant through a HGP with the help of booster blower.
Beside the ignition fan, there are three fresh air fans and one
recirculation fan supplying fresh air and recirculated to 17 wind boxes of the
sinter machine. The gases above the both updraft wind boxes are low in
sulphur dioxide extremely humid and at low temperature. These gases are
mixed with the hot gases from the discharge end of the sinter machine
recirculated to the last three wind boxes at the discharge end of the sinter
machine. There are five cyclones for dust removal of ventilation air and
recirculation gases in order to avoid any dust build up in the ducts and also to
avoid wear of the fans.
3.1.4 SINTER AND RETURN FINES HANDLING
The lumps discharge from sinter m/c at 800 deg. C are first crushed by a claw
breaker up to about 250 mm. a vibrating feeder feed the materials to a spike
roll crusher to get particles of size 130 mm which are conveyed to a vibrating
feeder and a Ross classifier . The 65-130 mm fraction is sent to ISF by a tray
conveyor. The 7-65 mm fraction from classifier is sent to an intermediate bin.
From here the material can either go to intermediate storage or to crushing
circuit for return fines. In the return crushing circuit the material goes to a
corrugated roll crusher and a smooth roll crusher through vibrating feeders to
get a size less than 8 mm, the finally crushed hot material is sent to cooling
drum where the bay house dust is also added. The cooling is accomplished by
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addition of different slurries generated in ISF plant, cadmium plant, copper
plant and industrial water. The moisture content of the cooled material is in the
industrial water. The moisture content of the cooled material is in the range of
2-35% and this material is carried back to sinter proportioning plant.
3.1.5 VENTILATION SYSTEM
The dry ventilation gases from all machines, belt conveyors and material
transmission point are cleaned in a central bag filter. The mixing and cooling
drum dusts are removed at above 100 deg. C. by a burner system and the gases
are dusted in a separate bag filter. The removed dust is sent to return fines
circuit.
Ventilation gases and vapors from the return fines bin are treated in
venture scrubber units. The washed gases are vented after passing through
hydro clones. The wash solution is collected in an agitated tank from where the
solution is recalculating to the venture scrubber units.
3.1.6 SLURRY HANDLING
In general, the slurry received from ISF, cadmium plant and copper plant are
treated in agitated tank and fed into cooling drum. The various slurry-handling
units are located in the crusher building.
3.1.7 RECIRCULATION FAN
The Main uses of recirculation fan as depicted above are:
1. It is used for reutilization of the heat of SO2 gas and supply it to bed
again
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2. It is used for cooling purpose.
3.2 ZINC CIRCUIT
3.2.1 IMPERIAL SMELTING PLANT
The I.S.F. is one of the plants of the C.L.Z.S. in this plant, the small sized
clinkers coming from the sinter plant are melted and lead, silver, zinc, and
copper are obtained in their impure form. These impure metals are then sent to
refinery in order to obtain the highest purity form.
Fig 4 Imperial Smelting Furnace
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Fig.5 Process Flow Diagram
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3.2.1.1 PROCESS:
In sinter plant, the raw material after conveyed through a belt, is mixed with
water and heated in a furnace and it forms spherical shaped clinkers of size
about 25-30 kg. After this, these are subjected to hammering in a big machine
and small sized products of 1-2 kg are formed.
In Imperial smelting furnace (I.S.F.), these clinkers are kept in sinter
bins of capacity 300 tones. These are two bins, one on the left and other on the
rights. After this, these sinter products reaches the screen feeder (vibrator) a
dare stored in way hopper, which works as small storage having open for a
definite time period and it closes as soon as it fills completely.
The coke required for combustion is stored in coke yard and is
transferred through cold coke bin. This coke is sent to coke screen feeder.
There is preheated at a temperature of 400-500 deg Celsius the CO gas is
obtained from this heating.
Air is blown into the stove by the help of an 1800 KW blower. The
reaction between air and coke produces carbon monoxide. Enormous amount
of heat is obtained by firing the air. This heat basically smelts the metal oxide
into elemental metal. Molten Lead metal falls into the bottom of the furnace
from where it is tapped together with slag of molten gangue material. At the
temperature of operation, metallic zinc is formed as a vapor and rises up the
furnace shaft with the furnace gases. These zinc containing gases pass through
a furnace off take into the condenser containing molten lead. Here zinc is
condensed to a liquid by shock cooling, the gases with a spray of finely
divided droplets of lead generated by rotors immersed in the lead. After
absorbing condensed zinc, this lead is pumped out of the condenser into an
adjacent cooling launder where it is cooled by tube banks immersed in the
launder from above. At the end of the launder the zinc lead is treated with flux
and flows into a separation bath where, at the cool temperature of 440 deg.
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Cent., zinc separates as a molten layer on the top of lead. Zinc continuously
overflows via a V – notch into a adjacent liquation bath whilst the main lead
stream passes from the separation bath under the underflow weir and then
into a return launder leading back into the condenser. The liquation bath is
small bath in which any final separation of lead and iron from the zinc can
occur before the zinc overflows to the final holding bath. Here it is allowed to
accumulate before being tapped for casting or further treatment in zinc
refinery. The waste gases leaves the condenser after zinc is condensed from
them are passed into a gas. These gases contain carbon monoxide and have a
low calorific value. After cleaning, calorific value is utilized in preheating the
furnace blast air and in preheating the cokes any remaining excess is used in
the site power plant boilers.
3.2.2 ZINC REFINERY PLANT
Fig. 6 Zinc Refinery
3.2.2.1 OBJECTIVES FOR REFINING:
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The I.S.F zinc is not suitable for zinc’s prime user i.e. galvanizers due to
1) High cadmium percentage
2) Occasional high arsenic
Hence zinc produced from I.S.F. needs a suitable refining tobecome of
economic industrial use. The process followed in CLZS is by distillation in
“new jersey type distillation columns”
3.2.2.2 INTRODUCTION:
Zinc refinery is situated east of I.S.F. the basic engineering is given by
mechim-engineering of Belgium and process by novellas-godault of France.
Main construction is done by TATA DAVY LTD.
3.2.2.3 FEATURES:
1. Since the main refining is done in columns consisting of superimposed
silicon-carbide trays, the trays can’t take thermal shock, so the process
can’t be stopped more than 2-3 minutes. Only after the life (2 to 3 yr) of
the columns finishes can be stopped. So the equipments which are
responsible for feeding and heating must run 24hr/day.
2. Due to above reason, there are some conditions before start up. Otherwise
huge expenditure & time will be taken to rebuild the trays consisting
columns.
3.2.2.4 PROCESS
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The I.S.F. Zinc is feed to the storage f/c through tilting device or by the
loading door in form of 1.1T ingots. This Zn by gravity goes to the feeding
furnace. In emergency 1 zinc pump is used or ladles are tilted in the feeding f/c
directly. The feeding furnace through the needle valve and float valve feeds
the I.S.F. Zinc to the lead columns in requite amount and temp. The lead
columns which have 59 trays each are having two parts up to the 30th tray. It is
having a combustion chamber around it and is known as the boiling part. The
top portion above the 34th tray (feed tray) is insulated, it is the refluxing part.
Only during the start up this top part of lead columns are electrically
heated.
If we consider the column erected by superimposition the trays, has got 8
types of trays. The top tray is different at it is connected to the condensers by a
mall-rack (electro-fused silica) cross over the bottom tray, the tray above feed
tray. The 30thtray is having double opening and extra electric coils around it.
33rd tray is having different outer shape. All the rest trays are of 2 types.
1. flat type: located in the reflux part
2. w-type: located in the bottom part (boiling part)
If we consider the composition of I.S.F. Zn and see the action of combustion
chamber which is having 8 burners in each column drawing 10% of total
combustion air from the burner and the rest 90% preheated air from
recuperator, we find that full cadmium, half Zn vaporizes and full lead and half
Zn comes down, the top product is condensed in condensers of each lead
column and then again in hot condition they are fed to cadmium columns. Feed
system is same as lead columns, Here the number of trays are 56 only and 2
columns are there (rest everything is same for cadmium columns) this feed is
known as Zn-Cd alloy. This Lead is separated in liquation f/c. some hard Zn
also comes and rest Zn having only the minimum lead comes out as G.O.B.
Zinc i.e. good ordinary brand or prime western (PW) zinc. The top Zn-Cd
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alloy is separated in cadmium columns. The bottom product of this is very
high grade Zinc known as Special High Grade Zinc (SHG).The top product
after condensation becomes Cd-Zn enriched alloy and is casted moulds to be
sent to Cd refinery. The SHG & GOB are casted in separate casting m/c.
CHAPTER 4
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TRANDUCERS & INSTRUMENTS
4.1 DISTRIBUTED CONTROL SYSTEM
A distributed control system (DCS) usually refers to a manufacturing system,
process or any kind of dynamic system, in which the controller elements are
not central in location (like the brain) but are distributed throughout the system
with each component sub-system controlled by one or more controllers. The
entire system of controllers is connected by networks for communication and
monitoring.
DCS is a very broad term used in a variety of industries, to monitor and
control distributed equipment. A DCS typically uses custom designed
processors as controllers and uses both proprietary interconnections and
Communications protocol for communication. Input & output modules form
component parts of the DCS. The processor receives information from input
modules and sends information to output modules. The input modules receive
information from input instruments in the process (a.k.a. field) and transmit
instructions to the output instruments in the field.
4.1.1 APPLICATIONS
Distributed Control Systems (DCSs) are dedicated systems used to control
manufacturing processes that are continuous or batch-oriented, such as oil
refining, petrochemicals, central station power generation, pharmaceuticals,
cement production, steelmaking, and papermaking. DCSs are connected to
sensors and actuators and use set-point control to control the flow of material
through the plant. The most common example is a set-point control loop
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consisting of a pressure sensor, controller, and control valve . Pressure or flow
measurements are transmitted to the controller, usually through the aid of a
signal conditioning Input/output (I/O) device. When the measured variable
reaches a certain point, the controller instructs a valve or actuation device to
open or close until the fluidic flow process reaches the desired set-point. Large
oil refineries have many thousands of I/O points and employ very large DCSs.
Processes are not limited to fluidic flow through pipes, however, and can also
include things like paper machines and their associated variable speed drives
and motor control centers, cement kilns, mining operations, ore processing
facilities, and many others.
A typical DCS consists of functionally and/or geographically distributed
digital controllers capable of executing from 1 to 256 or more regulatory
control loops in one control box. The input/output devices (I/O) can be integral
with the controller or located remotely via a field network. Today’s controllers
have extensive computational capabilities and, in addition to proportional,
integral, and derivative (PID) control, can generally perform logic and
sequential control.
DCSs may employ one or several workstations and can be configured at
the workstation or by an off-line personal computer. Local communication is
handled by a control network with transmission over twisted pair, coaxial, or
fiber optic cable. A server and/or applications processor may be included in
the system for extra computational, data collection, and reporting capability.
4.1.2 USE OF DCS IN PLANT
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1. Distributed Control Systems (DCSs) are used to control manufacturing
processes that are continuous or batch-oriented, such as refining Process
(lead, zinc silver).
2. The whole process of the plant is controlled by DCS so that the plant can
work automatically
4.2 PROGRAMMABLE LOGIC CONTROLLER (PLC):
INSTALLED AT: Serve as the centre for monitoring, controlling and
measuring all the parameters in control room. PLC in short act as the important
computer to control the process flow.
FIG.7 PLC Working
4.2.1 PRINCIPLE:
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A programmable logic controller (PLC) or programmable controller is a digital
computer used for automation of electromechanical processes, such as control
of machinery on factory assembly lines, amusement rides, or lighting _xtures.
PLCs are used in many industries and machines, such as packaging for
multiple inputs and output arrangements, extended temperature ranges and
semiconductor machines unlike general-purpose computers, the PLC is
designed immunity to electrical noise, and resistance to vibration and impact.
Programs control machine operations are typically stored in battery-backed or
non-volatile memory. A PLC is an example of a real time system since output
results must be produced in response to input conditions within a bounded
time, otherwise unintended operation will result.
4.3 THERMOCOUPLE
Fig 8 Thermocouple
A thermocouple is a junction between two different metals that produces a
voltage related to a temperature difference. Thermocouples are a widely used
type of temperature sensor and can also be used to convert heat into electric
power. They are cheap and interchangeable, have standard connectors, and can
measure a wide range of temperatures. The main limitation is accuracy;
System errors of less than one Kelvin (K) can be difficult to achieve.
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Thermocouples are widely used in science and industry; a few applications
would include temperature measurement for kilns, measurement of exhaust
temperature of gas turbines or diesel engines, and many other industrial
processes.
4.3.1 PRINCIPLE OF OPERATION
When any conductor is subjected to a thermal gradient, it will generate a
voltage. This is now known as the thermoelectric effect or See beck effect.
Any attempt to measure this voltage necessarily involves connecting another
conductor to the "hot" end. This additional conductor will then also experience
the temperature gradient, and develop a voltage of its own which will oppose
the original. Fortunately, the magnitude of the effect depends on the metal in
use. Using a dissimilar metal to complete the circuit creates a circuit in which
the two legs generate different voltages, leaving a small difference in voltage
available for measurement. That difference increases with temperature, and
can typically be between 1 and 70 micro volts per degree Celsius (µV/°C) for
the modern range of available metal combinations. Certain combinations have
become popular as industry standards, driven by cost, availability,
convenience, melting point, chemical properties, stability, and output. This
coupling of two metals gives the thermocouple its name.
Thermocouples measure the temperature difference between two points,
not absolute temperature. In traditional applications, one of the junctions—the
cold junction—was maintained at a known (reference) temperature, while the
other end was attached to a probe
4.3.2 APPLICATIONS
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Thermocouples are suitable for measuring over a large temperature range, up
to 2300 °C. They are less suitable for applications where smaller temperature
differences need to be measured with high accuracy, for example the range 0–
100 °C with 0.1 °C accuracy. For such applications, thermistors and resistance
temperature detectors are more suitable.
4.4 RTD
There are two broad categories, "film" and "wire-wound" types.
Film thermometers have a layer of platinum on a substrate; the layer may be
extremely thin, perhaps one micrometer. Advantages of this type are relatively
low cost and fast response. Such devices have improved in performance
although the different expansion rates of the substrate and platinum give
"strain gauge " effects and stability problems.
Fig 9 Film Type
Wire-wound thermometers can have greater accuracy, especially for wide
temperature ranges. The coil diameter provides a compromise between
mechanical stability and allowing expansion of the wire to minimize strain and
consequential drift.
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Fig 10 Wire Wound
4.4.1 WORKING
Resistance thermometers require a small current to be passed through in order
to determine the resistance. This can cause resistive heating, and
manufacturers' limits should always be followed along with heat path
considerations in design. Care should also be taken to avoid any strains on the
resistance thermometer in its application. Lead wire resistance should be
considered, and adopting three and four wire connections can eliminate
connection lead resistance effects from measurements - industrial practice is
almost universally to use 3-wire connection. 4-wire connections need to be
used for precise application.
4.4.2 ADVANTAGES:
Advantages of platinum resistance thermometers:
● High accuracy
● Low drift
● Wide operating range
● Suitability for precision applications.
4.4.3 LIMITATIONS:
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● RTDs in industrial applications are rarely used above 660 °C. At
temperatures above 660 °C it becomes increasingly difficult to prevent
the platinum from becoming contaminated by impurities from the metal
sheath of the thermometer. This is why laboratory standard
thermometers replace the metal sheath with a glass construction. At very
low temperatures, say below -270 °C (or 3 K), due to the fact that there
are very few phonons, the resistance of an RTD is mainly determined by
impurities and boundary scattering and thus basically independent of
temperature. As a result, the sensitivity of the RTD is essentially zero
and therefore not useful.
● Compared to thermistors, platinum RTDs are less sensitive to small
temperature changes and have a slower response time. However
thermistors have a smaller temperature range and stability.
BIBLIOGRAPHY
1. Vedanta Resources
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2. Industrial Instrumentation and Control (S.K. SINGH)
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