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1

COMPANY

PROFILE

INDIANOIL CORPORATION LIMITED

VISION

A major diversified, translational, integrated energy company with

national leadership and its strong environment conscience, playing a national

role in oil security and public distribution.

DISTINCTIONS

IndianOil is India‘s flagship national oil company with business

interests straddling the entire hydrocarbon value chain – from refining, pipeline

transportation and marketing of petroleum products to exploration & production

of crude oil & gas, marketing of natural gas and petrochemicals. It is the leading

Indian corporate in the Fortune 'Global 500' listing, ranked at the 125th position in

the year 2010.

With over 34,000-strong workforce, IndianOil has been helping to meet

India‘s energy demands for over half a century. With a corporate vision to be the

Energy of India, IndianOil closed the year 2009-10 with a sales turnover of Rs.

271,074 crore and profits of Rs. 10,221 crore.

At IndianOil, operations are strategically structured along

business verticals - Refineries, Pipelines, Marketing, R&D Centre and Business

Development – E&P, Petrochemicals and Natural Gas. To achieve the next

level of growth, IndianOil is currently forging ahead on a well laid-out road

map through vertical integration— upstream into oil exploration & production

(E&P) and downstream into petrochemicals – and diversification into

natural gas marketing and alternative energy, besides globalisation of its

downstream operations. Having set up subsidiaries in Sri Lanka, Mauritius and

the United Arab Emirates (UAE), IndianOil is simultaneously scouting for new

business opportunities in the energy markets of Asia and Africa.

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Indian Oil and its subsidiary (CPCL) account for over 48% petroleum products

market share, 34.8% national refining capacity and 71% downstream sector

pipelines capacity in India.

The IndianOil Group of companies owns and operates 10 of India's 20

refineries with a combined refining capacity of 65.7 million metric tonnes per

annum (MMTPA, .i.e. 1.30 million barrels per day approx.). IndianOil‘s

cross-country network of crude oil and product pipelines, spanning 10,899 km and

the largest in the country, meets the vital energy needs of the consumers in an

efficient, economical and environment-friendly manner.

IndianOil has a keen customer focus and a formidable network of

customer touch-points dotting the landscape across urban and rural India. It has

18,643 petrol and diesel stations, including 2,947 Kisan Seva Kendras (KSKs) in

the rural markets. With a countrywide network of 35,600 sales points, backed for

supplies by 140 bulk storage terminals and depots, 98 aviation fuel stations and

88 LPGas bottling plants, IndianOil services every nook and corner of the

country. Indane is present in almost 2764 markets through a network of 5095

distributors. About 7,593 bulk consumer pumps are also in operation for the

convenience of large consumers, ensuring products and inventory at their doorstep.

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It has a portfolio of powerful and much-loved energy brands that includes

Indane LPGas, SERVO lubricants, XtraPremium petrol, XtraMile diesel,

etc. Validating the trust of 56.8 million households, Indane has earned the coveted

status of ‗Superbrand‘ in the year 2009.

IndianOil‘s ISO-9002 certified Aviation Service commands an enviable

63% market share in aviation fuel business, successfully servicing the demands of

domestic and international flag carriers, private airlines and the Indian Defence

Services. The Corporation also enjoys a 65% share of the bulk consumer, industrial,

agricultural and marine sectors.

With a steady aim of maintaining its position as a market leader and

providing the best quality products and services, IndianOil is currently investing

Rs. 47,000 crore in a host of projects for augmentation of refining and

pipelines capacities, expansion of marketing infrastructure and product quality

upgradation.

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Innovation is Key

IndianOil has a sprawling world-class R&D Centre that is perhaps Asia's

finest. It conducts pioneering work in lubricants formulation, refinery

processes, pipeline transportation and alternative fuels, and is also the nodal agency

of the Indian hydrocarbon sector for ushering in Hydrogen fuel economy in the

country. The Centre holds 215 active patents, including 109 international patents.

Some of the in-house technologies and catalysts developed by Indian

Oil include the INDMAX technology (for maximising LPGas yield), Oilivorous–S

bio- remediation technology (extended to marine applications too), Diesel

Hydro DeSulphurisation (DHDS) catalyst, a special Indicat catalyst for Bharat

Stage-IV compliant Diesel, IndVi catalyst for improved distillate yield and FCC

throughput, and adsorbent based deep desulphurisation process for gasoline and diesel

streams.

Natural Gas marketing is another thrust area for IndianOil with special

focus on City Gas Distribution (CGD) business. The Corporation has entered into

franchise agreements with several CGD players to market Compressed Natural Gas

through its retail outlets. IndianOil‘s joint venture with GAIL India Ltd. - Green

Gas Ltd. – is authorised to take up city gas distribution in Agra. A long term gas

supply agreement

has been signed with NTPC. IndianOil is setting up a 5 MMTPA LNG import,

storage & regassification terminal at Ennore (outskirts of Chennai). This LNG

Terminal would be first of its kind on the East Coast of India.

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IndianOil R & D Centre, Faridabad

IndianOil corporation Limited is the country‘s largest commercial

enterprise, with a sale turnover of Rs.1,30,203 crore and profits of Rs. 7,005 crore

for fiscal 2003.

IndianOil is India‘s sole representative in Fortune‘s prestigious listening of

the world‘s 500 largest corporations, ranked 191 for the year 2003 based on

fiscal 2002 performance. It is also the seventeen largest petroleum company in

the world. Indian oil has been adjudged first in petroleum trading among the

national oil company in the Asia-Pacific region, and is ranked 325th in the

Forbes‘ ―Global 500‖ listing of the largest public companies apart from the

global 500, Forbes has also come out with the ―Forbes Global 2000‖, a

comprehensive listening of the world‘s biggest and most important companies.

This list includes 2000 companies from 46 countries.

IndianOil‘s world class R&D centre spread over 65 acres of lush green

campus on the outskirts of Delhi has state of the art facilities and has carried out

pioneering work in lubricants formulation, refinery processes and pipeline

transportation. The centre has 108 patents to its credit of which 44 are international

including 26 in USA.

IndianOil's world class R&D Centre, established in 1972, has state-of –the

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art facilities and has delivered pioneering results in lubricants technology,

refining process, pipeline transportation, bio-fuels and fuel-efficient appliances.

Over the past three decades, IndianOil R&D Centre has developed

over thousands of formulations of lubricating oils and greases responding to the

needs of Indian industry and consuming sectors like Defence, Railways, Public

Utilities and Transportation. The Centre has also developed and introduced many new

lubricant products to the Indian market like multigrade railroad oils.

Focused research in the areas of lubricants and grease

formulations, fuels, refining processes, biotechnology, additives, pipeline

transportations, engine evaluation , tribiological and emission studies, and applied

metallurgy has won several awards. The R&D Center‘s activities in refining

technology are targeted in the areas of fluid catalytic cracking (FCC),

hydroprocessing, catalysis, reside upgradation, distillation simulation and

modeling, lube processing, crude evaluation, process optimization, material

failure analysis and remaining life assessment and technical services to operating

units.

In FCC, apart from process optimization and catalyst evaluation the accent is on

the development of novel technologies aimed at value addition to various refinery

streams. IndianOil's R&D Centre is fully equipped to provide technical support to

commercial hydrocracker units in the evaluation of feedstocks and catalysts,

optimization of operating parameters, evaluation of licensors' process technologies,

development of novel processes and simulation models.

Material failure analysis and remaining life assessment of refinery equipment

and installations is a highly specialized service being provided by the R&D Centre to the

refineries of IndianOil as well as other companies.

With a vision of evolving into a leader as technology provider through

excellence in management of knowledge, technology and innovation, Indian Oil has

launched IndianOil Technology Ltd. The new subsidiary markets the intellectual

properties developed by IndianOil R&D Centre.

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IndianOil Technologies Limited

IndianOil offers services in the field of Research and Development. The

clientele includes defence, railways, automotive oil manufactures, textile producers,

industries producing steel, ferroalloys, power plant industries and multinational

companies involved in the business of petroleum products, petrochemicals and bio

fuels etc. IndianOil R&D Centre also provides expertise to universities, IITs and other

academic institutions for collaborative programmes and joint research ventures.

DIVISIONS IN R & D CENTRE

The centre has been divided into the following divisions:

1. Lubricant Technology

2. Analytical division(AD)

3. Engine testing and tribology(ETT)

4. Vehicle testing and fuel emissions

5. Chemical engineering divisions

6. Hydro processing division

7. Technology promotion division

8. Quality standards and documentation

9. Technical co- ordination division

10. Management and information system

11. Synthetics

12. Biotic

13. Greases

14. Applied metallurgy

15. Instrumentation

16. Petrochemical

17. Personnel and administration

18. Finance

19. Material department

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Lubricant technology

This is the core division, which plays important role in the formation of lubes and

additives; this division is further divided into four groups namely

1. Fuel research group

2. Automotive oil group

3. Industrial oil group

4. Metal working oils

5. Synthetic lubes

Condition monitoring lab, which is used to find out the condition of used sample

with robotic instrument, is the attractive feature of this division.

Analytical division

The main function of this group is to provide analytical support to all the research

additives in the centre. This group performs the chemical analysis of both fresh and

used samples. Analytical constitutes three groups:

1. Separation methods

2. Molecular spectroscopy

3. Atomic spectroscopy

Engine testing and tribology

Performance evaluation of newly developed automotive lubricants in prescribed

standard engines is must before commercialization. These tests, varying in duration

from few hours to thousands of hours for individual tests, determine the efficiency to

the end use products. The engine tests laboratory has 36 test benches including

standard engines and also earns lots of money for the organization. Tribology

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division evaluates the performance of industrial lubricants, metal working and

greases.

Vehicle testing of fuels and emissions

Once the new formulation passes in engine testing, that formation will be tested in

this department, this department tests the performance of oils in real/ simulated

driving conditions for fuel economy , emissions and its performance of lubes. The

field trial laboratory has been set up where 8 dynamometers are used to simulate all

the driving conditions at ambient temperature for different types of vehicles. This

department is equipped with test rings for two wheelers as well as four wheelers.

Climatic chamber is also available, and it facilitates the testing under varying

conditions and humidity condition.

Robotic driver for two wheelers adds the ability to test the performance of

formulations for longer duration.

Chemical processing division

This department mainly pays attention on the refining processes like Fluid catalytic

cracking, resid fluid catalytic cracking (RFCC), reforming. Delayed coking and

visebreaking. Pilot plants are there to carry out the experimental studies for all the

above mentioned areas. Micro reactors are also there for the preliminary screening of

the catalysts.

Hydro processing division

This division plays an important role in the production of cleaner fuels that meets

environmental and emission specification. This division focuses much on the

processes involving hydrogen like hydro treating, hydrocracking and hydrogen

production. This division is broadly divided into catalyst group, evaluation group,

modelling and simulation group, and design cell.

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Technology promotion department

This group takes effort in promotion of the technologies developed at R & D centre.

It is an interface between R & D (Lube technology), marketing and customers. Once

the formulation given by the PDD passed all the laboratory tests it will arrange final

field trials and produce OEM approvals, it will also conduct customer awareness

programs.

Quality standards and documentation

Library, ISO certification and patent filling are the major activities of this

department. Presently the library is computerized and any information regarding the

books/journals/articles and their availability can be obtained from any networked

computer in our R & D centre. IOC has 15 patents to its credit in both refining

technology and lube technology.

Technical co-ordination department

This division acts as an interface between R & D centre and refineries. Other

activities include contribution to corporate planning, technology forecasting.

Research activities:

1. Crude evaluation: facilities are there for the post-mortem of crude.

2. Lube processing related research: it mainly pays attention on the secondary

process like solvent extraction and its optimization. They have come up with

a new concept like co-solvent in the extraction.

Information systems

This department takes care of the IT related issues of the centre. Functions are to

procure all software and hardware required by the centre. Presently, the main activity

is to implement LIMS and they are also taking part in project ―MANTHAN‖, i.e.

connecting all offices of Indian Oil with Intranet.

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Synthetics and biotic

The main aim of the synthetics department is to indigenise all the additives; those

will be blended in base oils to get lubricants. Right now research is going on

developing additives like anti-oxidants, anti-wear agents, extreme pressure additives,

detergency, rust and corrosion inhibitors. This department is also having pilot plant

for additive manufacture. Biotic department also does routine analysis for toxicity

and bio degradability of formulation. Major areas of research include development of

biocatalysts and development of a biochemical process for de-sulphurisation of

diesel.

Grease

The main activity of grease department is in development of the formulations for the

new greases. Greases are solid or semi-solid with having particles of sizes greater

than colloids that are suspended in base oils to provide non flowing lubrication.

Apart from the pilot facilities it also have facilities to find out the properties such as

many cone penetration, dropping pant, roll stability, water resistance, water

absorption, low temperature torque, sheer tats, rust test, etc.

Applied metallurgy

Function of this division is-

1. Material failure analysis

2. Remaining life assessment

3. Condition monitoring equipment at high pressure and high temperature conditions.

Some of the facilities available in this department are universal tester, scanning

electron microscope, micro hardness tester, stereoscopic zoom microscopic,

advanced optical microscope , impact testing machine, corrosion wheel etc.

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Instrumentation

Instrumentation department carries out all the repair and calibration work of

instruments.

Personnel and administration

This division takes care of the employee‘s needs. They will help employees to get

their accommodation and all other things. Other activities include recruitment of

suitable professionals, assistance in transportation and loan facilities.

Materials department

Function of this section is mainly to procure chemicals and equipment , required in

the R & D centre. This department has got two divisions, one each for indigenous

procurement and for imports.

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Chapter 1

TEMPERATURE SENSORS

The seven basic types of temperature sensors are:

1.1 RTD

1.1.1. What Is an RTD?

An RTD (Resistance Temperature Detector) is basically a temperature sensitive

resistor. It is a positive temperature coefficient device, which means that the

resistance increases with temperature. The resistance of the metal increases with

temperature. The resistive property of the metal is called its resistivity. The resistive

property defines length and cross sectional area required to fabricate an RTD of a

given value. The resistance is proportional to length and inversely proportional to the

cross sectional area :

R= (r X L)/A

Where

R = Resistance (ohms)

r = Resistivity (ohms)

L = Length

A = Cross sectional area

1.2. RTD Materials

The criterion for selecting a material to make an RTD is:

the material must be malleable so that it can be formed into small wires.

it must have a repeatable and stable slope or curve.

the material should also be resistant to corrosion.

the material should be low cost

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it is preferred that the material have a linear resistance verses temperature

slope

Some of the common RTD materials are:

1.2.1. Platinum: The platinum RTD has the best accuracy and stability among the

common RTD materials. The resistance versus temperature curve is fairly linear and

the temperature range is the widest of the common RTD materials. Platinum has a

very high resistivity, which means that only a small quantity of platinum is required

to fabricate a sensor and making platinum cost competitive with other RTD

materials. Platinum is the only RTD commonly available with a thin film element

style.

1.2.1.1 Primary uses:

Platinum is the primary choice for most industrial, commercial, laboratory and other

critical RTD temperature measurements. Copper, nickel and nickel iron are also

commonly used RTD materials. They are mostly used in lower cost noncritical

applications.

Platinum RTD Performance Specifications :

1.2.1.2 Temperature Coefficient (µ):

Platinum RTDs are manufactured with two distinct types or temperature coefficients

(µ).

The temperature coefficient (µ) is the slope of the platinum RTD between 0°C to

100°C. It is calculated as follows:

(R100 - R0)/ (100xR0) = µ

µ= Temperature Coefficient (W/W/°C)

R100 = RTD resistance at 100°C

R0 = RTD resistance at 0°C

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1.2.2. DIN Grade Platinum:

The DIN grade, sometimes referred to as the European standard, has a temperature

coefficient of 0.00385W/W/°C (+/- 0.000012). A consortium of European standards

committees developed the curve that all manufacturers of platinum RTDs could

conform to. The platinum that is used to achieve the DIN standard is pure platinum

that is alloyed with a controlled small amount of platinum group metals to reproduce

the curve. The DIN curve has captured a majority of the market for industrial RTDs

worldwide. Thin film sensors are only manufactured with DIN platinum.

1.2.3. Reference Grade Platinum:

Reference grade platinum is made from 99.999% pure platinum. It will produce a

maximum temperature coefficient of 0.003926W/W/°C. The maximum temperature

coefficient can only be achieved in Standard Platinum Resistance Thermometers

(SPRT) for laboratory use. The practical range of temperature coefficients for

industrial use is 0.003902 to 0.003923W/W/°C. Reference grade platinum is still the

choice for critical applications including aerospace and nuclear.

1.2.4 Accuracy:

Platinum RTDs typically are provided in two classes, class A and Class B.

Class A is considered high accuracy and has an ice point tolerance of +/- 0.06 ohms.

Class B is standard accuracy and has an ice point tolerance of +/-0.12 ohms. Class B

is widely used by most industries.

The accuracy will decrease with temperature. Class A will have an accuracy of +/-

0.43 ohms (+/-1.45°C) at600°C and class B will be +/- 1.06 ohms(+/- 3.3°C) at

600°C.

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1.3. RTD Types :

There are basically three styles of platinum sensing elements.

Each style has unique characteristics and advantages.

1.3.1. Wire wound Element : The wire wound sensor is the simplest sensor design.

The sensing wire is wrapped around an insulating mandrel or core. The winding core

can be round or flat, but must be an electrical insulator. Matching the coefficient of

thermal expansion of the sensing wire and winding core materials will minimize any

mechanical strain.

Strain on the element wire will result in an error in the measurement. The winding

core must also be selected to match the intended service temperature and

environment.

The sensing wire is connected to a larger wire, usually referred to as the element lead

or wire. This wire is selected to be compatible with sensing wire so that the

combination does not generate an emf that would distort the measurement. The wire

also has to be able to with stand any annealing during the process.

The wire wound sensor is the only configuration that can be made with all5of the

sensing materials.

This design is intended for Aerospace or Nuclear applications, where response time

is important or the application is of a critical nature.

The sensing element is wound on a hollow stainless steel winding core that is

insulated with a flame sprayed coating aluminium oxide. A specific stainless steel is

chosen for its close match of thermal expansion with the platinum sensing wire.

After the usual processing, annealing and coating, the sensing element is enclosed in

cased with a thin stainless steel sheath. This provides a completely sealed sensing

element that can be directly immersed into a process fluid.

Response time for this sensor ranges from 350 milli-seconds for a directly immersed

sensor to approximately 11seconds in an appropriately fitted thermo well.

The disadvantage of this style sensing element is the high cost.

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1.3.2. Coiled Element :

The coiled sensor is a method to produce a "strain free" design. A strain free design

allows the sensing wire to expand and contract free of influences from other

materials in the assembly. Techniques similar to those used in this design are used in

Standard Platinum Resistance Thermometers (SPRT), which are used as laboratory

standards.

There are variations to this style sensor depending on the manufacturer. The basis of

the sensing element is a small coil of platinum sensing wire. This coil resembles a

filament in an incandescent light bulb. The housing or mandrel is a hard fired

aluminium oxide tube with four equally spaced bores that run transverse to the axes.

The coil is inserted in the bores of the mandrel and the bores are packed with a very

fine grit ceramic powder. This permits the sensing wire to move while still remaining

in good thermal contact with the process being measured.

The strain free design provides the highest temperature coefficient

(.003923ohm/ohm/°C) available for industrial use. It also has the best accuracy and

long term stability. The response time is a little slower than an outer wound sensor.

1.3.3. Thin Film Element: The thin film sensing element is manufactured by

depositing a very thin layer of platinum on a ceramic substrate. This layer is usually

just a 10 to 100 angstroms (10-8 centimetres ) thick. The platinum film is coated with

epoxy or glass. This coating helps protect deposited platinum film and acts as a strain

relief for the external lead wires.

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1.3.4. Leadwire Configurations:

1.3.4.1. Two wire RTD:

The two wire RTD is the simplest wire configuration. One wire is attached to each

side of the element. A measure can be taken by any device equipped to measure

resistance, including basic Volt Ohm Meters (VOM).This is the least accurate way of

measuring temperature, due to the fact that the lead wire resistance is in series with

the sensing element. The lead wire is at a different temperature than the sensing

element and also has different resistance verses temperature characteristics. The

longer the leads wire the greater the effect on the measurement.

1.3.4.2. Three Wires RTD:

The three wires RTD is the most popular configuration for use in industrial

applications. When used correctly, the three wire configuration eliminates the series

resistance. This permits an accurate measurement of the sensing element. Two of the

leads are connected to one side of the sensing element and the single lead to the other

side.

The resistance in L1 and L3 should be matched as close as possible; this will cause

the lead resistance to cancel them.

The colour code for a three wire RTD is two red wires and one white.

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1.3.4.3. Four Wire RTD:

A four wire RTD is the most accurate method to measure an RTD. It is primarily

used in laboratories and is seldom seen in an industrial application. A four wire RTD

circuit removes the effect of mismatched resistances on the lead wires. A constant

current is passed through L1and L4. L2 and L3 measure the voltage drop across the

RTD element.The colour code for a four wire RTD is usually two red wires and two

white wires.

Figure A is a 2 wire RTD.

Figure B is a 3 wire RTD.

Figure C is a 4 wire RTD.

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1.4. Thermocouples

A thermocouple is a device that consists of two measuring devices connected

via two wires made up of different materials to a common end. A sufficient

thermoelectric difference between the two materials is essential for detection

purposes. Usually Platinum- Constantan are used as the materials for the wire. One

junction is usually referred to as the hot junction while the other junction is referred

to as the cold junction.

Heating the measuring junction of thermocouple produces a voltage across

the reference junction. Difference between two voltages is proportional to the

difference in temperature which is measured on voltmeter. Thermocouples are

voltage devices that indicate temperature by measuring a change in voltage. As

temperature goes up, the output voltage of the thermocouple rises - not necessarily

linearly.

Often the thermocouple is located inside a metal or ceramic shield that

protects it from exposure to a variety of environments. Metal-sheathed

thermocouples also are available with many types of outer coatings, such as Teflon,

for trouble-free use in acids and strong caustic solutions.

Of the infinite number of candidate combinations, the ISA recognizes 12.

Most of these thermocouple types are known by a single-letter designation; the most

common are J, K, T, and E. The compositions of thermocouples are international

standards, but the color codes of their wires are different. For example, in the U.S.

the negative lead is always red, while the rest of the world uses red to designate the

positive lead.

Measurement errors can be easily introduced with thermocouples. Since the

voltage created by the thermocouple is due to the bonding of two dissimilar metals,

the introduction of other junctions to the circuit results in voltage changes that are

referred to as cold junction errors. If the temperature at the connections is

determined, these errors can be corrected by a process called cold junction

compensation. This is carried out at the receiving device, which is usually the signal

conditioner.

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Thermocouples are also available in three junction types: grounded, ungrounded, and

exposed.

Thermocouples come in three junction types. Grounded units have their

sensing junction directly attached to the probe wall (A), ensuring good heat transfer

from the outside to the junction. The junction point of the ungrounded type (B) is

detached from the probe wall, resulting in a slower response time than offered by the

grounded devices. The exposed thermocouple (C), with its sensing junction outside

the sheath and exposed to the environment, is preferable when a quick response time

is required.

The grounded thermocouple has its sensing junction directly attached to the

probe wall. This results in good heat transfer from the outside, through the probe

wall to the thermocouple junction

The ungrounded thermocouple has its junction point detached from the probe

wall. This type has a response time that is slower than the grounded style .When

response time is the determining factor in selecting a thermocouple probe type, the

exposed thermocouple is preferable .In this type of probe, the sensing junction

protrudes out of the tip of the sheath and is exposed to the surrounding environment.

Ungrounded thermocouples offer the best response time, but cannot be used in

corrosive or pressurized applications.

Temperature measurement decisions can make or break the expected results

of the process. Choosing the correct sensor for the application might be a difficult

task, but processing that measured signal is also very critical.

1.4.1. Tip-sensitive Thermocouples

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The probe sensing tip is constructed of copper alloy which is twenty times more

conductive than stainless steel. The sensors react more quickly to changes and

indicate tip temperature instead of stem temperature. The result is better accuracy in

thermo wells, bearings, and other installations.

1.5. Infrared Sensors

Infrared sensors are non-contacting sensors. As an example, if you hold up a

typical infrared sensor to the front of your desk without contact, the sensor will tell

you the temperature of the desk by virtue of its radiation - probably 68°F at normal

room temperature.

In a noncontacting measurement of ice water, it will measure slightly under

0°C because of evaporation, which slightly lowers the expected temperature reading.

1.6. Bimetallic Devices

Bimetallic devices take advantage of the expansion of metals when they are

heated. In these devices, two metals are bonded together and mechanically linked to

a pointer. When heated, one side of the bimetallic strip will expand more than the

other. And when geared properly to a pointer, the temperature is indicated.

Advantages of bimetallic devices are portability and independence from a

power supply. However, they are not usually quite as accurate as are electrical

devices, and you cannot easily record the temperature value as with electrical devices

like thermocouples or RTDs; but portability is a definite advantage for the right

application.

1.7. Thermometers

Thermometers are well-known liquid expansion devices. Generally speaking,

they come in two main classifications: the mercury type and the organic, usually red,

liquid type. The distinction between the two is notable, because mercury devices

have certain limitations when it comes to how they can be safely transported or

shipped.

For example, mercury is considered an environmental contaminant, so

breakage can be hazardous. Be sure to check the current restrictions for air

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transportation of mercury products before shipping.

1.8. TRANSDUCERS

Introduction:

Transducers are devices that convert one type of physical phenomenon,

such as temperature, strain, pressure, or light into another. The most

common transducers convert physical quantities to electrical quantities,

such as voltage or resistance. Transducer characteristics define many of

the signal conditioning requirements of your measurement system. Table

1 summarizes the basic characteristics and conditioning requirements of

some common transducers.

Table 1.1.: Electrical Characteristics and Basic Signal Conditioning Requirements

of

Common Transducers

Sensor Electrical

Characteristics

Signal Conditioning

Requirement

Thermocouple Low-voltage

output Low

sensitivity

Nonlinear output

Reference temperature

sensor (for cold-

junction

compensation)

High amplification

Linearization

RTD Low resistance

(100 ohms typical)

Low sensitivity

Nonlinear output

Current excitation

Four-wire/three-

wire configuration

Linearization Strain gauge Low

resistance

device

Low sensitivity

Nonlinear output

Voltage or

current

excitation

High

amplification

Bridge

completion

Linearization

Shunt

calibration

Current output device Current loop output

(4 – 20 mA typical)

Precision resistor

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Thermistor Resistive device

High resistance

and sensitivity

Very nonlinear

output

Current excitation or

voltage excitation

with reference

resistor Linearization AC Linear Variable Differential

Transformer (LVDT)

AC voltage output AC

excitation

Demodulatio

n

Linearization

1.8.1. THERMOCOUPLES:

The most popular transducer for measuring temperature is the

thermocouple. The thermocouple is an inexpensive, rugged device that can operate

over a very wide range of temperatures. However, the thermocouple has unique

signal conditioning requirements.

A thermocouple operates on the principle that the junction of two

dissimilar metals generates a voltage that varies with temperature. Measuring

this voltage is difficult because connecting the thermocouple to the terminals of a

DAQ board creates what is called the reference junction or cold junction,

shown in Fig.2.1. These additional junctions act as thermocouples themselves

and produce their own voltages. Thus, the final measured voltage, VMEAS,

includes both the thermocouple and cold junction voltages. The method used to

compensate for these unwanted cold-junction voltages is called cold-junction

compensation.

Fig. : The connection of thermocouple wires to a measurement system

There are two general approaches to cold-junction compensation --

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hardware and software compensation. Hardware compensation uses a special

circuit that applies the appropriate voltage to cancel the cold-junction voltage.

Although you need no software for hardware compensation, each thermocouple

type must have its own compensation circuit that works at all ambient

temperatures.

Cold-junction compensation in software, on the other hand, is very flexible

and requires only knowing the ambient temperature. If you use an additional

sensor to directly measure the ambient temperature at the cold junction, you can

compute the appropriate compensation for the unwanted thermoelectric voltages.

Software cold- junction compensation follows this process:

1. Measure the temperature of the reference junction and compute the

equivalent thermocouple voltage for this junction using standard

thermocouple tables or polynomials.

2. Measure the output voltage (VMEAS) and add -- not subtract -- the reference-

junction voltage computed in Step 1.

3. Convert the resulting voltage to temperature using standard

thermocouple polynomials or look-up tables.

Sensitivity is another characteristic to consider with

thermocouple measurements. Thermocouple outputs are very low level and

change only 7 to 50 µV for every 1 °C change in temperature. You can increase

the sensitivity of the system with a low-noise, high-gain amplification of the

signal.

The same DAQ board with a signal conditioning amplifier gain of 1000

has a resolution of 2.4 µV/bit, which corresponds to a fraction of a degree

Celsius. More importantly, an external signal conditioner can amplify the low-

level thermocouple signal near the source to minimize noise corruption. A

high-level amplified signal suffers much less corruption from radiated noise

in the environment. Table 2.2 summarizes various types of thermocouples

along with their materials and temperature ranges.

26

Table1.2: Temperature ranges of various types of thermocouples along with their

used materials.

Types Materials Temperature Ranges J Fe-Co -210oC/+1210oC

K Cr-Al -270oC/+1370oC T Cu-Co -270oC/+400oC R Pt13%Rh-Pt -50oC/+1760oC S Pt10%Rh-Pt -50oC/+1760oC B Pt30%Rh-Pt6%Rh 0oC/+1820oC E Cr-Co -270

oC/+1000

oC

N Nicrosil-Nisil -270oC/+400

oC (1)

0oC/+1300

oC (2)

(1): Wires dia. 0.32mm (2): Wires dia. 1.63 mm

1.8.2. STRAIN GAUGES:

The strain gauge is the most common device used in mechanical testing and

measurements. The most common type is the bonded resistance strain gauge,

which consists of a grid of very fine foil or wire. The electrical resistance of the

grid varies linearly with the strain applied to the device. When using a strain

gauge, you bond the strain gauge to the device under test, apply force, and

measure the strain by detecting changes in resistance. Strain gauges are also used

in sensors that detect force or other derived quantities, such as acceleration,

pressure, and vibration. These sensors generally contain a pressure sensitive

diaphragm with strain gauges mounted to the diaphragm.

Because strain measurement requires detecting relatively small changes

in resistance, the Wheatstone bridge circuit is almost always used. The

Wheatstone bridge circuit consists of four resistive elements with a voltage

excitation supply applied to the ends of the bridge. Strain gauges can occupy

one, two or four arms of the bridge, with any remaining positions filled with

fixed resistors. Fig. 2.4 shows a configuration with a half-bridge strain gauge

consisting of two strain gauge elements, RG1 and RG2, combined with two fixed

resistors, R1 and R2.

27

When the ratio of RG1 to RG2 equals the ratio of R1 to R2, the measured

voltage V0 is 0 V. This condition is referred to as a balanced bridge. As strain is

applied to the gauge, their resistance values change, causing a change in the

voltage at VO. Full- bridge and half bridge strain gauges are designed to maximize

sensitivity by arranging the strain gauge elements in opposing directions.

For example, the half-bridge strain gauge in Figure 5 includes an element RG1,

which is installed so that its resistance increases with positive strain, and an element

RG2, whose resistance decreases with positive strain. The resulting VO responds with

sensitivity that is twice that of a quarter-bridge configuration.

Some signal conditioning products have voltage excitation sources, as well as

provisions for bridge-completion resistors. Bridge completion resistors should be very

precise and stable. Because strain-gauge bridges are rarely perfectly balanced, some

signal conditioning systems also perform nulling. Nulling is a process in which you

adjust the resistance ratio of the unstrained bridge to balance the bridge and remove any

initial DC offset voltage. Alternatively, you can measure this initial offset voltage and use

this measurement in your conversion routines to compensate for unbalanced initial

condition.

28

Chapter 2

PID Control

2.1. What is a controller?

2.1.1. Working of temperature controllers

To accurately control process temperature without extensive operator involvement, a

temperature control system relies upon a controller, which accepts a temperature

sensor such as a thermocouple or RTD as input. It compares the actual temperature to

the desired control temperature, or setpoint, and provides an output to a control

element. The controller is one part of the entire control system, and the whole system

should be analyzed in selecting the proper controller. The following items should be

considered when selecting a controller:

1. Type of input sensor (thermocouple, RTD) and temperature range

2. Type of output required (electromechanical relay, SSR, analog output)

3. Control algorithm needed (on/off, proportional, PID)

4. Number and type of outputs (heat, cool, alarm, limit)

2.1.2. What Are the Different Types of Controllers, and How Do They Work?

There are three basic types of controllers: on-off, proportional and PID. Depending

upon the system to be controlled, the operator will be able to use one type or another

to control the process.

2.2. On/Off Control

An on-off controller is the simplest form of temperature control device. The output

from the device is either on or off, with no middle state. An on-off controller will

switch the output only when the temperature crosses the set point. For heating

control, the output is on when the temperature is below the set point, and off above

set point. Since the temperature crosses the set point to change the output state, the

process temperature will be cycling continually, going from below set point to above,

and back below. In cases where this cycling occurs rapidly, and to prevent damage to

29

contactors and valves, an on-off differential, or ―hysteresis,‖ is added to the

controller operations. This differential requires that the temperature exceed set point

by a certain amount before the output will turn off or on again. On-off differential

prevents the output from ―chattering‖ or making fast, continual switches if the

cycling above and below the set point occurs very rapidly. On-off control is usually

used where a precise control is not necessary, in systems which cannot handle having

the energy turned on and off frequently, where the mass of the system is so great that

temperatures change extremely slowly, or for a temperature alarm. One special type

of on-off control used for alarm is a limit controller. This controller uses a latching

relay, which must be manually reset, and is used to shut down a process when a

certain temperature is reached.

2.3. Proportional Control

Proportional controls are designed to eliminate the cycling associated with on-off

control. A proportional controller decreases the average power supplied to the heater

as the temperature approaches set point. This has the effect of slowing down the

heater so that it will not overshoot the set point, but will approach the set point and

maintain a stable temperature. This proportioning action can be accomplished by

turning the output on and off for short time intervals. This "time proportioning"

varies the ratio of ―on‖ time to "off" time to control the temperature. The

proportioning action occurs within a ―proportional band‖ around the set point

temperature. Outside this band, the controller functions as an on-off unit, with the

output either fully on (below the band) or fully off (above the band). However,

within the band, the output is turned on and off in the ratio of the measurement

difference from the set point. At the set point (the midpoint of the proportional band),

the output on:off ratio is 1:1; that is, the on-time and off-time are equal. if the

temperature is further from the set point, the on- and off-times vary in proportion to

the temperature difference. If the temperature is below set point, the output will be on

longer; if the temperature is too high, the output will be off longer.

30

2.4. PID Control

The third controller type provides proportional with integral and derivative control,

or PID. This controller combines proportional control with two additional

adjustments, which helps the unit automatically compensate for changes in the

system. These adjustments, integral and derivative, are expressed in time-based units;

they are also referred to by their reciprocals, RESET and RATE, respectively. The

proportional, integral and derivative terms must be individually adjusted or ―tuned‖

to a particular system using trial and error. It provides the most accurate and stable

control of the three controller types, and is best used in systems which have a

relatively small mass, those which react quickly to changes in the energy added to

the process. It is recommended in systems where the load changes often and the

controller is expected to compensate automatically due to frequent changes in set

point, the amount of energy available, or the mass to be controlled.

OMEGA offers a number of controllers that automatically tune themselves. These

are known as auto tune controllers.

2.4.1. In PID controllers, Proportional term

Plot of PV vs time, for three values of Kp (Ki and Kd held constant)

The proportional term (sometimes called gain) makes a change to the output that is

proportional to the current error value. The proportional response can be adjusted by

multiplying the error by a constant Kp, called the proportional gain.

The proportional term is given by:

31

where

Pout: Proportional term of output

Kp: Proportional gain, a tuning parameter

e: Error = SP − PV

t: Time or instantaneous time (the present)

A high proportional gain results in a large change in the output for a given change in

the error. If the proportional gain is too high, the system can become unstable). In

contrast, a small gain results in a small output response to a large input error, and a

less responsive (or sensitive) controller. If the proportional gain is too low, the

control action may be too small when responding to system disturbances.

2.4.2. Integral term

Plot of PV vs time, for three values of Ki (Kp and Kd held constant)

The contribution from the integral term (sometimes called reset) is proportional to

both the magnitude of the error and the duration of the error. Summing the

instantaneous error over time (integrating the error) gives the accumulated offset that

should have been corrected previously. The accumulated error is then multiplied by

the integral gain and added to the controller output. The magnitude of the

contribution of the integral term to the overall control action is determined by the

integral gain, Ki.

32

The integral term is given by:

where

Iout: Integral term of output

Ki: Integral gain, a tuning parameter

e: Error = SP − PV

t: Time or instantaneous time (the present)

τ: a dummy integration variable

The integral term (when added to the proportional term) accelerates the movement of

the process towards setpoint and eliminates the residual steady-state error that occurs

with a proportional only controller. However, since the integral term is responding to

accumulated errors from the past, it can cause the present value to overshoot the

setpoint value (cross over the setpoint and then create a deviation in the other

direction).

2.4.3. Derivative term

Plot of PV vs time, for three values of Kd (Kp and Ki held constant)

The rate of change of the process error is calculated by determining the slope of the

error over time (i.e., its first derivative with respect to time) and multiplying this rate

of change by the derivative gain Kd. The magnitude of the contribution of the

33

derivative term (sometimes called rate) to the overall control action is termed the

derivative gain, Kd.

The derivative term is given by:

where

Dout: Derivative term of output

Kd: Derivative gain, a tuning parameter

e: Error = SP − PV

t: Time or instantaneous time (the present)

The derivative term slows the rate of change of the controller output and this effect is

most noticeable close to the controller setpoint. Hence, derivative control is used to

reduce the magnitude of the overshoot produced by the integral component and

improve the combined controller-process stability. However, differentiation of a

signal amplifies noise and thus this term in the controller is highly sensitive to noise

in the error term, and can cause a process to become unstable if the noise and the

derivative gain are sufficiently large. Hence an approximation to a differentiator with

a limited bandwidth is more commonly used. Such a circuit is known as a Phase-

Lead compensator

Control theory is important for nearly all engineering disciplines. One of the simplest

control systems, for those who grow up in hot climates with central air conditioning,

is the thermostat. Nearly everyone has set the dial to the temperature you want and

then heard the air conditioning turn itself on and off to maintain

a house at a comfortable level. This is only one example. Modern aircraft are full of

complex control systems that maintain a steady aircraft during takeoff, landing, and

flight. The recent scooter 'IT' has a control system that keeps the two-wheeled

scooter balanced and responds when the user leans in a certain direction. In all these

systems the system takes measurements of the current state, and through

software , hardware, or both the system moves to the desired state. In this course we

will only be providing an introduction to control theory. Advanced control theory can

34

be quite complex and rely on advanced mathematical techniques. In this course we

will concentrate mostly on building the systems and

implementing simple software control algorithms. The control method that we will

discuss is referred to as PI control (Proportional, Integral). PI control uses a

combination of three simple control methods to maintain a set point.

This document will explain PI algorithms and we will implement them in the

simulation of control of first order systems: specifically, we will work through the

example of a first order thermal system.

PID controller

2.4.4 Understanding a PID Controller

The PID temperature controller is the most sophisticated controller available. Three

levels of tuning - Proportional, Integral, and Derivative - provide exceptional

performance at a surprisingly low price. But what is it, really??

The characteristics and performance of many devices change with a change in

temperature making them difficult to use in a particular operation. The change in

temperature is caused by a change in environment. To hold characteristics constant in

a changing environment we must supply or remove heat to compensate for variations

in ambient temperature. This is accomplished with temperature controllers.

Most installations of temperature controllers supply heat, or remove heat (chill), to

hold the temperature at a constant point somewhat above or below the ambient

temperature. Electronic temperature controllers are most often used to vary the

supply of an electric current through a resistance heater to accomplish this when the

controlled temperature is to be above ambient.

The controlled device or material can also be stabilized at some temperature below

environment by controlling the flow of a refrigerant through a heat exchanger. Yet

another type of low temperature control system (called buck and boost) supplies

cooling to drop the temperature below the desired set point and then controls the

temperature by supplying heat via a controller to get the exact temperature setting.

35

This type of operation is needed when the desired set point is close to the ambient

temperature.

In an ideal world, once we set the temperature of an area or device, the temperature

would remain the same over any length of time. Unfortunately we do not live in an

ideal world. Thus, the need for temperature controllers.

If one were to observe the temperature of a controlled item over a period of time it

would be rare to always find that item at the exact target (set point) temperature.

Temperature would vary above and below the set point most of the time. What we

are concerned about, therefore, is the amount of variation. One of the newer

temperature controller designs uses a sophisticated means of reducing this variation.

This controller is known as a PID controller.

2.5. PID CONTROLLER DEFINITIONS

In order to understand the operation of a PID (Proportional-Integral-Differential)

controller we should review a few basic definitions.

Derivative - is a value which expresses the rate of change of another value. For

instance, the derivative of distance is speed.

Integral - is the opposite of a derivative. The integral of acceleration is velocity and

the integral of velocity is distance.

Proportional - means a value varying relative to another value. The output of a

proportional controller is relative to (or a function of) the difference between the

temperature being controlled and the set point. The controller will be full on at some

temperature which is well below the set point (or desired temperature). It will be full

off at some point above the set point.

The classical three-term PID controller

Proportional feedback control can reduce error responses but that it still allows a

non-zero steady-state error for a proportional system.In addition, proportional

36

feedback increases the speed of response but has a much larger transient overshoot.

When the controller includes a term proportional to the integral of the error, then the

steady-state error can be eliminated.

But this comes at the expense of further deterioration in the dynamic response.

Addition of a term proportional to the derivative of the error can damp the dynamic

response. Combined, these three kinds of actions form the classical PID controller,

which is widely used in industry.

This principle mode of action of the PID controller can be explained by the parallel

connection of the P, I and D elements shown in Figure 2.1. From this diagram the

transfer function of the PID controller is

(Eq.2.1)

Figure 2.1: Block diagram of the PID controller

The controller variables are

gain

integral action time

derivative action time

37

Eq. (2.1) can be rearranged to give

(2.2)

These three variables, and are usually tuned within given ranges. Therefore, they are

often called the tuning parameters of the controller. By proper choice of these tuning

parameters a controller can be adapted for a specific plant to obtain a good behavior

of the controlled system.

It follows from Eq. (2.2) that the time response of the controller output is

(2.3)

Using this relationship for a step input of , i.e. , the step response of the PID

controller can be easily determined. The result is shown in Figure 2.2a. One has to

observe that the length of the arrow of the D action is only a measure of the weight

of the impulse.

Figure 2.2: Step responses (a) of the ideal and (b) of the real PID controller

In the previous considerations it has been assumed that a D behaviour can be realised

by the PID controller. This is an ideal assumption and in reality the ideal D element

cannot be realised. In real PID controllers a lag is included in the D behaviour.

Instead of a D element in the block diagram of Figure 2.1a element with the transfer

function

38

(2.4)

is introduced. From this the transfer function of the real PID controller or more

precisely of the controller follows as

(2.5)

Introducing the controller tuning parameters

and

it follows

(2.6)

The step response of the controller is shown in Figure 2.2b. This response from gives

a large rise, which declines fast to a value close to the P action, and then migrates

into the slower I action. The P, I and D behaviour can be tuned independently. In

commercial controllers the 'D step' at can often be tuned 5 to 25 times larger than the

'P step'. A strongly weighted D action may cause the actuator to reach its maximum

value, i.e. it reaches its 'limits'.

As special cases of PID controllers one obtains for:

a) (2.7)

39

the PI controller with transfer function

b) the ideal PD controller with the transfer function

(2.8)

and the controller with the transfer function

(2.9)

c)

and the P controller with the transfer function

(2.10)

The step responses of these types of controllers are compiled in Figure 2.3. A pure I

controller may also be applied and this has the transfer function

(2.11)

40

Figure 2.3: Step responses of the PID controller family

2.6. Control Loop Tuning

It is important to keep in mind that understanding the process is fundamental to

getting a well designed control loop. Sensors must be in appropriate locations and

valves must be sized correctly with appropriate trim.

In general, for the tightest loop control, the dynamic controller gain should be as high

as possible without causing the loop to be unstable. C

2.6.1. Fine Tuning "Rules"

This picture shows the effects of a PI controller with too much or too little P or I

action. The process is typical with a dead time of 4 and lag time of 10. Optimal is

red.

You can use the picture to recognize the shape of an optimally tuned loop. Also see

the response shape of loops with I or P too high or low. To get your process response

to compare, put the controller in manual change the output 5 or 10%, then put the

controller back in auto.

41

P is in units of proportional band. I is in units of time/repeat. So increasing P or I,

decreases their action in the picture.

Starting PID Settings For Common Control Loops

Loop Type PB

%

Integral

min/rep

Integral

rep/min

Derivative

min Valve Type

Flow 50 to

500

0.005 to

0.05 20 to 200 none

Linear or Modified

Percentage

Liquid

Pressure

50 to

500

0.005 to

0.05 20 to 200 none

Linear or Modified

Percentage

Gas Pressure 1 to 50 0.1 to 50 0.02 to 10 0.02 to 0.1 Linear

Liquid Level 1 to 50 1 to 100 0.1 to 1 0.01 to

0.05

Linear or Modified

Percentage

Temperature 2 to 100 0.2 to 50 0.02 to 5 0.1 to 20 Equal Percentage

Chromatograph 100 to

2000 10 to 120

0.008 to

0.1 0.1 to 20 Linear

These settings are rough, assume proper control loop design, ideal or series algorithm

and do not apply to all controllers.

2.6.2. Ziegler-Nichols Method:

1. First, note whether the required proportional control gain is positive or

negative. To do so, step the input u up (increased) a little, under manual

control, to see if the resulting steady state value of the process output has also

moved up (increased). If so, then the steady-state process gain is positive and

the required Proportional control gain, Kc, has to be positive as well.

2. Turn the controller to P-only mode, i.e. turn both the Integral and Derivative

modes off.

3. Turn the controller gain, Kc, up slowly (more positive if Kc was decided to be

so in step 1, otherwise more negative if Kc was found to be negative in step 1)

and observe the output response. Note that this requires changing Kc in step

42

increments and waiting for a steady state in the output, before another change

in Kc is implemented.

4. When a value of Kc results in a sustained periodic oscillation in the output (or

close to it), mark this critical value of Kc as Ku, the ultimate gain. Also,

measure the period of oscillation, Pu, referred to as the ultimate period. (

Hint: for the system A in the PID simulator, Ku should be around 0.7 and 0.8 )

5. Using the values of the ultimate gain, Ku, and the ultimate period, Pu, Ziegler

and Nichols prescribes the following values for Kc, tI and tD, depending on

which type of controller is desired

Table 2.1. Ziegler-Nichols Tuning Chart:

Kc I D

P control Ku/2

PI control Ku/2.2 Pu/1.2

PID control Ku/1.7 Pu/2 Pu/8

As an alternative to the table above, another set of tuning values have been

determined by Tyreus and Luyblen for PI and PID, often called the TLC tuning

rules. These values tend to reduce oscillatory effects and improves robustness.

Table 2.2. Tyreus-Luyben Tuning Chart:

Kc I D

PI control Ku/3.2 2.2 Pu

PID control Ku/2.2 2.2 Pu Pu/6.3

43

Chapter 3

Temperature Control of a liquid using PID control algorithm

3.1 Apparatus Used:

CHINO LT230- PID controller

PT100- Temperature Sensor.

Connecting Wires

Solenoid Contactor

Electric Heater

3.2. DIGITAL INDICATING CONTROLLER LT230 Series

LT230 series, 1/16 DIN size, new digital indicating controllers feature all functions

including newly developed PID algorithms and overshoot suppression function

which are convenient in various control applications.

3.2.1. Features

Two kinds of universal input

(Standard and for high temperature)

New PID algorithms built-in

New overshoot suppression function built-in

MODBUS protocol communications for easy

44

system configuration

Various functions are built in for easy control.

Only 7mm thickness of the front panel

Conformance to CE, UL and CSA

(UL, CSA: Approval pending

Water-protection conforming to IP65 (option)

3.2.2. TERMINAL BOARD

45

Table3.1.1 Line A: Control output 1 Table 3.1.2 Line B:

Communications/remote contacts

input/CT input

Table 3.1. Line C : Event output/control output 2/power supply

No.

On-off pulse type

SSR drive pulse

type Current output

type

Voltage output type 1 COM ＋

2 NO －

No. RS-485 Remote

contacts

input

CT input

6 SA

7 SB

8 SG DI-COM

9 DI1+ CT

10 DI2+ CT

No. Event output Control output 2

+ event output

AC power DC power

11 EV1 EV1

12 EV2 NO

13 COM1/2 COM

14 L (live) ＋

15 N (neutral) －

46

3.2.3. Measuring Ranges

Note: For DC current input, a shunt resistor (250 ) is necessary.

Inputs Input ranges Standard

universal

High

temperature

universal

Thermocouple B 0 to 1820°C 32 to 3300°F

R 0 to 1760°C 32 to 3200°F

S 0 to 1760°C 32 to 3200°F

N 0 to 1300°C 32 to 3250°F

K -200 to 1370°C -300 to 2450°F

E -199.9 to

700.0°C

-300 to 1250°F -

J -199.9 to

900.0°C

-300 to 1650°F -

T -199.9 to 400.0°C -300 to 700°F -

U -199.9 to 400.0°C -300 to 700°F -

L -199.9 to 900.0°C -300 to 1650°F -

WRe5-

WRe26

0 to 2310°C 32 to 4190°F -

W-WRe26 0 to 2310°C 32 to 4190°F -

PtRh40-

PtRh20

0 to 1880°C 32 to 3400°F -

Platinel II 0 to 1390°C 32 to 2500°F -

Resistance

thermometers

Pt100 -199.9 to 850.0°C -300 to 1500°F

JPt100 -199.9 to 649.0°C -300 to 1200°F

DC voltage 5V 0 to 5V (0.000 to

5.000)

Scale setting range

-1999 to 9999

Decimal point

position adjustable

DC current 20mA* 4 to 20mADC

(Converted into 1

to 5V)

47

3.2.4.Specifications

Input Specifications

Input signal Thermocouple… Standard universal: B, R, S, N, K, E, J, T,

U, L

High temperature universal: B, R, S, N,

K, WRe5-WRe26, W-WRe26, PtRh40-

PtRh20, Platinel II

Resistance thermometer…Pt100, JPt100

DC voltage…0 to 5V

A 250 shunt resistor (sold separately) and the 5V (1 to

5V) are used.

Accuracy rating ±0.25% ± 1 digit (at reference operation conditions)

Reference junction

compensation accuracy

±1.0°C (23°C±10°C), ±2.0°C (-10°C to 50°C)

Measuring unit °C or °F

Sampling cycle About 0.5 second

Burnout Up scale (thermocouple input, resistance thermometer

input)

Measuring current Resistance thermometer … 110µA

Scaling Ranges/scales of DC voltage/current input are optional

settings.

(-1999 to 9999)

Scale decimal point 0 to 3

Control Specifications

Control cycle time Approx. 0.5 second

Control system On-off pulse type PID system

Current output type PID system

SSR drive pulse type PID system

48

Voltage output type PID system

* 2-position control is selectable.

Control setpoint 2 sets switching, 4-digit setting

Setpoint ramp function: Setpoint ramp unit …°C/minute (common to rising/falling)

Setpoint rising ramp: 0 to 9999 (0 = no operation)

Setpoint falling ramp: 0 to 9999 (0 = no operation)

PV start function …At SV change, power-on, Run/Ready

Auto-tuning Standard (Manual setting of PID constants enabled)

PID constants P… 0.1 (0.0) to 999.9% (0 = 2-position)

I… 0 to 9999 seconds

D… 0 to 9999 seconds

PID deadband (gap) 0.0 to 9.9%

Anti-reset windup High limit … 0.0 to 100.0%, Low limit … -100.0 to 0.0%

Overshoot suppression

function

On/off selectable

Control operation With direct/reverse action switching

Output specifications -off pulse type

Output

signal

… On-off pulse conductive signal

Contact

ratings

… Resistive

load:

100VAC 3A, 240VAC 3A,

30VDC 3A

Inductive

load:

100VAC 1.5A, 240VAC

1.5A, 30VDC 1.5A

Pulse cycle … Approx. 1 second to 180 seconds

ad ustable

Output signal … 4 to 20mADC

Load resistance … 600 or less

49

Output

signal

… On-off pulse voltage signal

At ON 12VDC ± 20% (load current …

20mA or less)

At OFF 0.8VDC or less

Puls

cycle

… Approx. 1 second to 180 seconds

adjustable

Output signal … 0 to 10VDC

Output resistance … Approx. 10

Load resistance … 50k or more

General Specifications

3.3. PT100 Platinum Resistance Thermometers

Platinum resistance thermometers (PRTs) offer excellent accuracy over a wide

temperature range (from -200 to +850 °C). Standard Sensors are are available from

many manufacturers with various accuracy specifications and numerous packaging

options to suit most applications. Unlike thermocouples, it is not necessary to use

special cables to connect to the sensor.

Rated power voltage 100V to 240VAC 50/60Hz universal power supply

Allowable power

voltage

90 to 264VAC

Working temperature

range

-10 to 50°C (maximum 40°C at closed installation)

Working humidity range 20 to 90%RH (no dew condensation)

Power consumption Maximum about 10VA

Installation Panel installation

Weight Maximum 200g

50

The principle of operation is to measure the resistance of a platinum element. The

most common type (PT100) has a resistance of 100 ohms at 0 °C and 138.4 ohms at

100 °C. There are also PT1000 sensors that have a resistance of 1000 ohms at 0 °C.

The relationship between temperature and resistance is approximately linear over a

small temperature range: for example, if you assume that it is linear over the 0 to 100

°C range, the error at 50 °C is 0.4 °C. For precision measurement, it is necessary to

linearise the resistance to give an accurate temperature. The most recent definition of

the relationship between resistance and temperature is International Temperature

Standard 90 (ITS-90).

This linearisation is done automatically, in software, when using Pico signal

conditioners. The linearisation equation is:

Rt = R0 * (1 + A* t + B*t2 + C*(t-100)* t3)

Where:

Rt is the resistance at temperature t, R0 is the resistance at 0 °C, and

A= 3.9083 E-3

B = -5.775 E-7

C = -4.183 E -12 (below 0 °C), or

C = 0 (above 0 °C)

For a PT100 sensor, a 1 °C temperature change will cause a 0.384 ohm change in

resistance, so even a small error in measurement of the resistance (for example, the

resistance of the wires leading to the sensor) can cause a large error in the

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measurement of the temperature. For precision work, sensors have four wires- two to

carry the sense current, and two to measure the voltage across the sensor element. It

is also possible to obtain three-wire sensors, although these operate on the (not

necessarily valid) assumption that the resistance of each of the three wires is the

same.

The current through the sensor will cause some heating: for example, a sense current

of 1 mA through a 100 ohm resistor will generate 100 µW of heat. If the sensor

element is unable to dissipate this heat, it will report an artificially high temperature.

This effect can be reduced by either using a large sensor element, or by making sure

that it is in good thermal contact with its environment.

Using a 1 mA sense current will give a signal of only 100 mV. Because the change in

resistance for a degree celsius is very small, even a small error in the measurement of

the voltage across the sensor will produce a large error in the temperature

measurement. For example, a 100 µV voltage measurement error will give a 0.4 °C

error in the temperature reading. Similarly, a 1 µA error in the sense current will give

0.4 °C temperature error.

Because of the low signal levels, it is important to keep any cables away from

electric cables, motors, switchgear and other devices that may emit electrical noise.

Using screened cable, with the screen grounded at one end, may help to reduce

interference. When using long cables, it is necessary to check that the measuring

equipment is capable of handling the resistance of the cables. Most equipment can

cope with up to 100 ohms per core.

The type of probe and cable should be chosen carefully to suit the application. The

main issues are the temperature range and exposure to fluids (corrosive or

conductive) or metals. Clearly, normal solder junctions on cables should not be used

at temperatures above about 170 °C.

Sensor manufacturers offer a wide range of sensors that comply with BS1904 class B

(DIN 43760): these sensors offer an accuracy of ±0.3 °C at 0 °C. For increased

accuracy, BS1904 class A (±0.15 °C) or tenth-DIN sensors (±0.03 °C). Companies

like Isotech can provide standards with 0.001 °C accuracy. Please note that these

52

accuracy specifications relate to the SENSOR ONLY: it is necessary to add on any

error in the measuring system as well.

3.4. Solenoid Contactor

A contactor is an electrically controlled switch used for switching a power circuit,

similar to a relay except with higher current ratings. A contactor is controlled by a

circuit which has a much lower power level than the switched circuit.

Contactors come in many forms with varying capacities and features. Unlike a circuit

breaker, a contactor is not intended to interrupt a short circuit current. Contactors

range from those having a breaking current of several amps and 24 V DC to

thousands of amps and many kilovolts. The physical size of contactors ranges from a

device small enough to pick up with one hand, to large devices approximately a

meter (yard) on a side.

Contactors are used to control electric motors, lighting, heating, capacitor banks, and

other electrical loads.

3.4.1 Operating principle

Unlike general-purpose relays, contactors are designed to be directly connected to

high-current load devices. Relays tend to be of lower capacity and are usually

designed for both normally closed and normally open applications. Devices

switching more than 15 amperes or in circuits rated more than a few kilowatts are

53

usually called contactors. Apart from optional auxiliary low current contacts,

contactors are almost exclusively fitted with normally open contacts. Unlike relays,

contactors are designed with features to control and suppress the arc produced when

interrupting heavy motor currents.

When current passes through the electromagnet, a magnetic field is produced, which

attracts the moving core of the contactor. The electromagnet coil draws more current

initially, until its inductance increases when the metal core enters the coil. The

moving contact is propelled by the moving core; the force developed by the

electromagnet holds the moving and fixed contacts together. When the contactor coil

is de-energized, gravity or a spring returns the electromagnet core to its initial

position and opens the contacts.

For contactors energized with alternating current, a small part of the core is

surrounded with a shading coil, which slightly delays the magnetic flux in the core.

The effect is to average out the alternating pull of the magnetic field and so prevent

the core from buzzing at twice line frequency.

Most motor control contactors at low voltages (600 volts and less) are air break

contactors; air at atmospheric pressure surrounds the contacts and extinguishes the

arc when interrupting the circuit. Modern medium-voltage motor controllers use

vacuum contactors. High voltage contactors (greater than 1000 volts) may use

vacuum or an inert gas around the contacts.

3.5. Electric Heater

54

3.6. Snapshot of the whole setup

55

Table 3.7. Readings

S.no. Time(Sec) Set Value (°C) Measured Value

(°C)

1 0 40 23.5

2 5 40 23.7

3 10 40 24.5

4 15 40 24.9

5 20 40 25.5

6 25 40 26.4

7 30 40 28.2

8 35 40 30.4

9 40 40 33.4

10 45 40 36.7

11 50 40 38.2

12 55 40 40.3

13 60 40 41.2

14 65 40 40.5

15 70 40 40.4

16 75 40 40.1

17 80 40 39.7

18 85 40 39.1

19 90 40 39.8

20 95 40 40.7

21 100 40 40.4

56

REFERENCES

BOOKS:

1. Instrumentation, Measurement And Analysis, B C Nakra & K.K

Chaudhry

2. A Course in Electrical and Electronics Measurements

&Instrumentation

by A.K. Sawhney Puneet , 18th Ed, Dhanpet Rai & Co. (P) Ltd.

WEBSITES:

1. http://www.chino.co.jp/english/products/01_LT230.htm

2. http://www.google.com

3. http://en.wikipedia.org/wiki/PID_controller

4. www.omega.com/temperature/z/pdf/z115-

117.pdf

.