Thermocouple Manual

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ADVANCE TECHNOLOGY Page 1www.atechindia.com

CONTENTS

TOPICS PAGES

(i) Introduction.2

(ii) Principle Of Operation...4

(iii) Types.......6

(iv) Application.........9

(v) Zigbee.....11

(vi) Block Diagram... 18

(vii) Working.19

(viii) Experiment20


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INTRODUCTION

A thermocouple consists of two conductors of different materials (usually metal alloys) that producea voltage in the vicinity of the point where the two conductors are in contact. The voltage produced

is dependent on, but not necessarily proportional to, the difference of temperature of the junction to

other parts of those conductors. Thermocouples are a widely used type of temperature sensor formeasurement and control and can also be used to convert a temperature gradient into electricity.

Commercial thermocouples are inexpensive, interchangeable, are supplied with standard

connectors, and can measure a wide range of temperatures. In contrast to most other methods oftemperature measurement, thermocouples are self powered and require no external form of

excitation. The main limitation with thermocouples is accuracy; system errors of less than one

degree Celsius (C) can be difficult to achieve

Any junction of dissimilar metals will produce an electric potential related to temperature.Thermocouples for practical measurement of temperature are junctions of specific alloys which
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have a predictable and repeatable relationship between temperature and voltage. Different alloys are

used for different temperature ranges. Properties such as resistance to corrosion may also beimportant when choosing a type of thermocouple. Where the measurement point is far from the

measuring instrument, the intermediate connection can be made by extension wires which are less

costly than the materials used to make the sensor.

Thermocouples are usually standardized against a reference temperature of 0 degrees Celsius;

practical instruments use electronic methods of cold-junction compensation to adjust for varyingtemperature at the instrument terminals. Electronic instruments can also compensate for the varying

characteristics of the thermocouple, and so improve the precision and accuracy of measurements.

Thermocouples are widely used in science and industry; applications include temperature

measurement for kilns, gas turbine exhaust, diesel engines, and other industrial processes.

A thermocouple measuring circuit with a heat source, cold junction and a measuring instrument

Principle of Operation
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In 1821, the GermanEstonian physicist Thomas Johann Seebeck discovered that when any

conductor is subjected to a thermal gradient, it will generate a voltage. This is now known as thethermoelectric effect or Seebeck 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 voltageof 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 legsgenerate different voltages, leaving a small difference in voltage available for measurement. That

difference increases with temperature, and is between 1 and 70 microvolt per degree Celsius

(V/C) for standard metal combinations.

The voltage is not generated at the junction of the two metals of the thermocouple but rather along

that portion of the length of the two dissimilar metals that is subjected to a temperature gradient.

Because both lengths of dissimilar metals experience the same temperature gradient, the end resultis a measurement of the difference in temperature between the thermocouple junction and the

reference junction.

Homogeneous material

A thermoelectric current cannot be sustained in a circuit of a single homogeneous material by the

application of heat alone, regardless of how it might vary in cross section. In other words,temperature changes in the wiring between the input and output do not affect the output voltage,

provided all wires are made of the same materials as the thermocouple.

Intermediate materials

The algebraic sum of the thermoelectric EMFs in a circuit composed of any number of dissimilar

materials is zero if all of the junctions are at a uniform temperature. So, if a third metal is inserted in

either wire and if the two new junctions are at the same temperature, there will be no net voltagegenerated by the new metal.

Successive or intermediate temperatures

If two dissimilar homogeneous materials produce thermal EMF1 when the junctions are at T1 and

T2 and produce thermal EMF2 when the junctions are at T2 and T3, the EMF generated when the

junctions are at T1 and T3 will be EMF1 + EMF2, provided T1


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Having a junction of known temperature, while useful for laboratory calibration, is not convenient

for most measurement and control applications. Instead, they incorporate an artificial cold junctionusing a thermally sensitive device such as a thermistor or diode to measure the temperature of the

input connections at the instrument, with special care being taken to minimize any temperature

gradient between terminals. Hence, the voltage from a known cold junction can be simulated, and

the appropriate correction applied. This is known as cold junction compensation. Some integratedcircuits are designed for cold junction temperature compensation for specific thermocouple types.

Grades

Thermocouple wire is available in several different metallurgical formulations per type, typically, in

decreasing levels of accuracy and cost: special limits of error, standard, and extension grades.

Extension grade wires made of the same metals as a higher-grade thermocouple are used to connect

it to a measuring instrument some distance away without introducing additional junctions betweendissimilar materials which would generate unwanted voltages; the connections to the extension

wires, being of like metals, do not generate a voltage.

In the case of platinum thermocouples, extension wire is a copper alloy, since it would be

prohibitively expensive to use platinum for extension wires. The extension wire is specified to have

a very similar thermal coefficient of EMF to the thermocouple, but only over a narrow range oftemperatures; this reduces the cost significantly.

The temperature-measuring instrument must have high input impedance to prevent any significantcurrent draw from the thermocouple, to prevent a resistive voltage drop across the wire. Changes in

metallurgy along the length of the thermocouple (such as termination strips or changes in

thermocouple type wire) will introduce another thermocouple junction which affects measurement

accuracy.

For typical metals used in thermocouples, the output voltage increases almost linearly with the

temperature difference (T) over a bounded range of temperatures. For precise measurements ormeasurements outside of the linear temperature range, non-linearity must be corrected. The

nonlinear relationship between the temperature difference (T) and the output voltage (a few mV)

of a thermocouple can be approximated by a polynomial:

The coefficients an are given for n from 0 to between 5 and 13 depending upon the metals. In some

cases better accuracy is obtained with additional non-polynomial terms. In modern equipment the

equation is usually implemented in a digital controller or stored in a look-up table; older devices useanalog circuits.
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Types

Certain combinations of alloys have become popular as industry standards. Selection of thecombination is driven by cost, availability, convenience, melting point, chemical properties,

stability, and output. Different types are best suited for different applications. They are usually

selected based on the temperature range and sensitivity needed. Thermocouples with lowsensitivities (B, R, and S types) have correspondingly lower resolutions. Other selection criteriainclude the inertness of the thermocouple material, and whether it is magnetic or not. Standard

thermocouple types are listed below with the positive electrode first, followed by the negative

electrode.

K

Type K (chromel {90% nickel and 10% chromium}alumel {95% nickel, 2% manganese, 2%

aluminium and 1% silicon}) is the most common general purpose thermocouple with a sensitivity ofapproximately 41 V/C, chromel positive relative to alumel. It is inexpensive, and a wide variety

of probes are available in its 200 C to +1250 C / -330 F to +2460 F range. Type K wasspecified at a time when metallurgy was less advanced than it is today, and consequently

characteristics may vary considerably between samples. One of the constituent metals, nickel, ismagnetic; a characteristic of thermocouples made with magnetic material is that they undergo a

deviation in output when the material reaches its Curie point; this occurs for type K thermocouples

at around 350 C.

E

Type E (chromelconstantan) has a high output (68 V/C) which makes it well suited to cryogenic

use. Additionally, it is non-magnetic. Wide range is -50 to 740 C and Narrow range is -110 to 140C.

J

Type J (ironconstantan) has a more restricted range than type K (40 to +750 C), but highersensitivity of about 55 V/C. The Curie point of the iron (770 C) causes an abrupt change in the

characteristic, which determines the upper temperature limit.

N

Type N (NicrosilNisil) (nickel-chromium-silicon/nickel-silicon) thermocouples are suitable for usebetween 270 C and 1300 C owing to its stability and oxidation resistance. Sensitivity is about

39 V/C at 900 C, slightly lower compared to type K.

Designed at the Defense Science and Technology Organization (DSTO), Australia, by Noel A

Burley, type N thermocouples overcome the three principal characteristic types and causes ofthermoelectric instability in the standard base-metal thermo element materials:
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1) A gradual and generally cumulative drift in thermal EMF on long exposure at elevatedtemperatures. This is observed in all base-metal thermo element materials and is mainly due

to compositional changes caused by oxidation, carburization or neutron irradiation that can

produce transmutation in nuclear reactor environments. In the case of type K, manganese

and aluminum elements from the KN (negative) wire migrate to the KP (positive) wire

resulting in a down-scale drift due to chemical contamination. This effect is cumulative and

irreversible.

2) A short-term cyclic change in thermal EMF on heating in the temperature range 250650 C,which occurs in types K, J, T and E thermocouples. This kind of EMF instability is

associated with structural changes like magnetic short range order.

3) A time-independent perturbation in thermal EMF in specific temperature ranges. This is dueto composition-dependent magnetic transformations that perturb the thermal EMFs in type K

thermocouples in the range 25-225 C, and in type J above 730 C.

4) Nicrosil and Nisil thermocouple alloys show greatly enhanced thermoelectric stabilityrelative to the other standard base-metal thermocouple alloys because their compositions

substantially reduces the thermoelectric instability. This is achieved primarily by increasing

component solute concentrations (chromium and silicon) in a base of nickel above those

required to cause a transition from internal to external modes of oxidation, and by selecting

solutes (silicon and magnesium) that preferentially oxidize to form a diffusion-barrier, and

hence oxidation inhibiting films.

Platinum types B, R, and S

Types B, R, and S thermocouples use platinum or a platinumrhodium alloy for each conductor.These are among the most stable thermocouples, but have lower sensitivity than other types,

approximately 10 V/C. Type B, R, and S thermocouples are usually used only for high

temperature measurements due to their high cost and low sensitivity.

B

Type B thermocouples use a platinumrhodium alloy for each conductor. One conductor contains

30% rhodium while the other conductor contains 6% rhodium. These thermocouples are suited for

use at up to 1800 C. Type B thermocouples produce the same output at 0 C and 42 C, limitingtheir use below about 50 C.
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R

Type R thermocouples use a platinumrhodium alloy containing 13% rhodium for one conductor

and pure platinum for the other conductor. Type R thermocouples are used up to 1600 C.

S

Type S thermocouples are constructed using one wire of 90% Platinum and 10% Rhodium (thepositive or "+" wire) and a second wire of 100% platinum (the negative or "-" wire). Like type R,type S thermocouples are used up to 1600 C. In particular, type S is used as the standard of

calibration for the melting point ofgold (1064.43 C).

T

Type T (copper constantan) thermocouples are suited for measurements in the 200 to 350 C

range. Often used as a differential measurement since only copper wire touches the probes. Since

both conductors are non-magnetic, there is no Curie point and thus no abrupt change incharacteristics. Type T thermocouples have a sensitivity of about 43 V/C.

C

Type C (tungsten 5% rheniumtungsten 26% rhenium) thermocouples are suited for measurementsin the 0 C to 2320 C range. This thermocouple is well-suited for vacuum furnaces at extremely

high temperatures. It must never be used in the presence ofoxygen at temperatures above 260 C.

M

Type M thermocouples use a nickel alloy for each wire. The positive wire (20 Alloy) contains 18%

molybdenum while the negative wire (19 Alloy) contains 0.8% cobalt. These thermocouples are

used in vacuum furnaces for the same reasons as with type C. Upper temperature is limited to1400 C. It is less commonly used than other types.

Chromel-gold/iron

In chromel-gold/iron thermocouples, the positive wire is chromel and the negative wire is gold witha small fraction (0.030.15 atom percent) of iron. It can be used for cryogenic applications (1.2300

K and even up to 600 K). Both the sensitivity and the temperature range depends on the iron

concentration. The sensitivity is typically around 15 V/K at low temperatures and the lowestusable temperature varies between 1.2 and 4.2 K.

Aging of thermocouples

Thermo elements are often used at high temperatures and in reactive furnace atmospheres. In thiscase the practical lifetime is limited by aging. The thermoelectric coefficients of the wires in a

thermocouple that is used to measure very high temperatures change with time, and the
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measurement voltage accordingly drops. The simple relationship between the temperature

difference of the joints and the measurement voltage is only correct if each wire is homogeneous.As thermocouples age in a process their conductors can lose homogeneity due to chemical and

metallurgical changes caused by extreme or prolonged exposure to high temperatures. If the

inhomogeneous section of the thermocouple circuit is exposed to a temperature gradient the

measured voltage will differ resulting in error. For this reason, aged thermocouples cannot be takenout of their installed location and recalibrated in a bath or test furnace to determine error. This also

explains why error can sometimes be observed when an aged thermocouple is pulled partly out of a

furnace -- as the sensor is pulled back, inhomogeneous sections may see exposure to increasedtemperature gradients from hot to cold as the inhomogeneous section now passes through the cooler

refractory area, contributing significant error to the measurement. Likewise, an aged thermocouple

that is pushed deeper into the furnace might sometimes provide a more accurate reading if beingpushed further into the furnace causes the area of in homogeneity to be located in an area of the

furnace where it is no longer exposed to a temperature gradient.

Applications

Thermocouples are suitable for measuring over a large temperature range, up to 2300 C.

Applications include temperature measurement for kilns, gas turbine exhaust, diesel engines, and

other industrial processes. They are less suitable for applications where smaller temperaturedifferences need to be measured with high accuracy, for example the range 0100 C with 0.1 C

accuracy. For such applications thermistors, silicon band gap temperature sensors and resistance

temperature detectors are more suitable.

Steel industry

Type B, S, R and K thermocouples are used extensively in the steel and iron industries to monitor

temperatures and chemistry throughout the steel making process. Disposable, immiscible, type Sthermocouples are regularly used in the electric arc furnace process to accurately measure the

temperature of steel before tapping. The cooling curve of a small steel sample can be analyzed and

used to estimate the carbon content of molten steel.

Heating appliance safety

Many gas-fed heating appliances such as ovens and water heaters make use of a pilot flame to ignitethe main gas burner when required. If it goes out, gas may be released, which is a fire risk and a

health hazard. To prevent this, some appliances use a thermocouple in a fail-safe circuit to sense

when the pilot light is burning. The tip of the thermocouple is placed in the pilot flame, generating a

voltage which operates the supply valve which feeds gas to the pilot. So long as the pilot flameremains lit, the thermocouple remains hot, and the pilot gas valve is held open. If the pilot light goes

out, the thermocouple temperature falls, causing the voltage across the thermocouple to drop and

the valve to close. Some combined main burner and pilot gas valves (mainly by Honeywell) reduce

the power demand to within the range of a single universal thermocouple heated by a pilot (25mVopen circuit falling by half with the coil connected to 10~12mV @ 0.2~0.25A typically) by sizing

the coil to be able to hold the valve open against a light spring, only after the initial turning-on force

is provided by the user pressing and holding a knob to compress the spring during first lighting.
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These systems are identifiable by the 'press and hold for x minutes' in the pilot lighting instructions.

(The holding current requirement of such a valve is much less than a bigger solenoid designed forpulling the valve in from closed would require.) Special test sets are made to confirm the valve let-

go and holding currents as an ordinary millimeter cannot be used as it introduces more resistance

than the gas valve coil. Apart from testing the open circuit voltage of the thermocouple, and the near

short-circuit DC continuity through the thermocouple gas valve coil, the easiest non-specialist test issubstitution of a known good gas valve.

Some systems, known as mill volt control systems, extend the thermocouple concept to both open

and close the main gas valve as well. Not only does the voltage created by the pilot thermocouple

activate the pilot gas valve, it is also routed through a thermostat to power the main gas valve aswell. Here, a larger voltage is needed than in a pilot flame safety system described above, and a

thermopile is used rather than a single thermocouple. Such a system requires no external source of

electricity for its operation and so can operate during a power failure, provided all the related

system components allow for this.

Note that this excludes common forced air furnaces because external power is required to operatethe blower motor, but this feature is especially useful for un-powered convection heaters. A similargas shut-off safety mechanism using a thermocouple is sometimes employed to ensure that the main

burner ignites within a certain time period, shutting off the main burner gas supply valve should that

not happen.

Out of concern for energy wasted by the standing pilot, designers of many newer appliances have

switched to an electronically controlled pilot-less ignition, also called intermittent ignition. With nostanding pilot flame, there is no risk of gas buildup should the flame go out, so these appliances do

not need thermocouple-based pilot safety switches. As these designs lose the benefit of operation

without a continuous source of electricity, standing pilots are still used in some appliances. The

exception is later model instantaneous (aka "tankless") water heaters that use the flow of water togenerate the current required to ignite the gas burner, in conjunction with a thermocouple as a safety

cut-off device in the event the gas fails to ignite, or the flame is extinguished.

Manufacturing

Thermocouples can generally be used in the testing of prototype electrical and mechanical

apparatus. For example, switchgear under test for its current carrying capacity may have

thermocouples installed and monitored during a heat run test, to confirm that the temperature rise atrated current does not exceed designed limits.

Power production

A thermocouple can produce current to drive some processes directly, without the need for extracircuitry and power sources. For example, the power from a thermocouple can activate a valve

when a temperature difference arises. The electrical energy generated by a thermocouple is

converted from the heat which must be supplied to the hot side to maintain the electric potential. Acontinuous transfer of heat is necessary because the current flowing through the thermocouple tends

to cause the hot side to cool down and the cold side to heat up (the Peltier effect).
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Thermocouples can be connected in series to form a thermopile, where all the hot junctions are

exposed to a higher temperature and all the cold junctions to a lower temperature. The output is thesum of the voltages across the individual junctions, giving larger voltage and power output. In a

radioisotope thermoelectric generator, the radioactive decay oftransuranic elements as a heat source

has been used to power spacecraft on missions too far from the Sun to use solar power.

Thermopiles heated by kerosene lamps were used to run battery less radio receivers in isolated

areas. There are commercially produced lanterns that use the heat from a candle to run several light-emitting diodes, and thermoelectrically-powered fans to improve air circulation and heat

distribution in wood stoves.

ZIGBEE

Zigbee is a collection of nodes organized into a cooperative network. Each node consists ofprocessing capability (one or more microcontrollers, CPUs or DSP chips), may contain multipletypes of memory (program, data and flash memories), have a RF transceiver (usually with a single

Omni- directional antenna), have a power source (e.g., batteries and solar cells), and accommodatevarious sensors and actuators. The nodes communicate wirelessly and often self-organize afterbeing deployed in an ad hoc fashion. Such systems can revolutionize the way we live and work.

Data acquisition and monitoring system using zigbees (WSNs) use tiny, inexpensive sensor nodeswith several distinguishing characteristics: they have very low processing power and radio ranges,permit very low energy consumption and perform limited and specific monitoring and sensingfunctions. Several such wireless sensors.

in a region self-organize and form a WSN. Information based on sensed data can be used inagriculture and livestock, assisted driving or even in providing security at home or in public places.

A key requirement from both the technological and commercial point of view is to provide adequatesecurity capabilities. Fulfilling privacy and security requirements in an appropriate architecture forWSNs offering pervasive services is essential for user acceptance. Five key features need to beconsidered when developing WSN solutions: scalability, security, reliability, self-healing androbustness.

Currently, data acquisition and monitoring system using zigbees are beginning to be deployed at anaccelerated pace. It is not Unreasonable to expect that in 10-15 years that the world will be coveredwith data acquisition and monitoring system using zigbees with access to them via the Internet. Thiscan be considered as the Internet becoming a physical network. This new technology is excitingwith unlimited potential for numerous application areas including environmental, medical, military,

transportation, entertainment, crisis management, homeland defense, and smart spaces. Since a dataacquisition and monitoring system using zigbee is a distributed real-time system a natural questionis how many solutions from distributed and real-time systems can be used in these new systems?
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SOLUTION

BASIC REQUIREMENTS

Low Power ConsumptionEase of Use

Scalability

Responsiveness

Range

Bi-Directional Communication

Reliability

Small Module Form Factor

COMMUNICATION NETWORKS

NETWORK TOPOLOGY

The basic issue in communication networks is the transmission of messages to achieve a prescribedmessage throughput (Quantity of Service) and Quality of Service (QoS). QoS can be specified interms of message delay, message due dates, bit error rates, packet loss, economic cost oftransmission, transmission power, etc. Depending on QoS, the installation environment, economicconsiderations, and the application, one of several basic network topologies may be used.

A communication network is composed of nodes, each of which has computing power and cantransmit and receive messages over communication links, wireless or cabled.

The basic network topologies are shown in the figure

Wireless LinksNumerous paths to Connect to the same destination.

These could be:-

1. Star2. Mesh3. Hybrid

A single network may consist of several interconnected subnets of different topologies. Networksare further classified as Local Area Networks (LAN), e.g. inside one building, or Wide AreaNetworks (WAN), e.g. between buildings


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STAR TOPOLOGY

All nodes of the star topology are connected to a single hub node. The hub requires greatermessage handling, routing, and decision-making capabilities than the other nodes. If a

communication link is cut, it only affects one node. However, if the hub is incapacitated thenetwork is destroyed. In the ring topology all nodes perform the same function and there is noleader node. Messages generally travel around the ring in a single direction.

However, if the ring is cut, all communication is lost. The self-healing ring network (SHR) shownhas two rings and is more fault tolerant.

In the bus topology, messages are broadcast on the bus to all nodes. Each node checks thedestination address in the message header, and processes the messages addressed to it.

The bus topology is passive in that each node simply listens for messages and is not responsible forretransmitting any messages.

Some features of star are:

Single Hop to GatewayGateway serves to communicate between nodes

Nodes cannot send data to each other directly

ProsLowest Power consumption

Easily Scalable

ConsNot very reliable as one point of failure

No alternate communication paths


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FULLY CONNECTED NETWORK

IT Suffer from problems of NP-complexity as additional nodes are added, the number of linksincreases exponentially. Therefore, for large networks, the routing problem is computationallyintractable even with the availability of large amounts of computing power.

MESH NETWORK

This type of network is regularly distributed networks that generally allow transmission only to anodes nearest neighbors. The nodes in these networks are generally identical, so that mesh nets arealso referred to as peer-to-peer (see below) nets. Mesh nets can be good models for large-scalenetworks of wireless sensors that are distributed over a geographic region, e.g. personnel or vehiclesecurity surveillance systems. Note that the regular structure reflects the communications topology;


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the actual geographic distribution of the nodes need not be a regular mesh. Since there are generallymultiple routing paths between nodes, these nets are robust to failure of individual nodes or links.An advantage of mesh nets is that, although all nodes may be identical and have the samecomputing and transmission capabilities, certain nodes can be designated as group leaders thattake on additional functions. If a group leader is disabled, another node can then take over theseduties.

Mesh Topology

Multi-Hopping Systems

Nodes can communicate with each other directly

Hybrid Topology

Sensors are arranged in a star topology around the routers The routersarrange themselves in a mesh form

RING TOPOLOGY

In Ring Topology all devices are situated in the form of a ring and each device connected withintwo neighbors devices by the means of communication. In Ring topology all node communicatewith each other clockwise or anti clockwise. Generally FDDI, Token ring and SONET used toconfigure ring topology. The use of ring topology increasing day by day because a network caneasily implement in home, office, building, and school .Ring topology have some benefits such asequal access to every one, transformation of data at very high speed but have disadvantages like Thefault in any cable or wire may cause of failure network., trouble shooting also a major problem.

APPLICATION OF INTERESTS

We categorize the applications into two classes.

1. The first class, data gathering applications, focuses on entity monitoring with limited signalprocessing requirements. The primary goal of these applications is to gather information of arelatively simple form, such as temperature and humidity, from the operating environment.Some environmental monitoring and habitat study applications also belong to this class.

2. The second class of applications requires the processing and transportation of large volumesof complex data. This class includes heavy industrial monitoring and video surveillance,where complicated signal processing algorithms are usually employed. We refer to theseapplications as computationally intensive applications.

In the following sections, we describe several academic and industrial applications based onthe above categorization. While both classes of applications are important for realizing thepotential of WSNs, the involved techniques can be quite deferent due to their varyingcomputation and communication demands


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DATA GATHERING APPLICATIONS

HABITAT STUDY

Habitat study is one of the driving applications for WSNs such applications usually require thesensing and gathering of bio-physical or bio-chemical information from the entities under study,such as Redwoods Storm Petrels Zebras and Oysters. In many scenarios, habitat study requiresrelatively simple signal processing, such as data aggregation using minimum, maximum, or averageoperations. Hence, motes are ideal platforms for such applications. The famous Great Duck Islandproject was initiated in the spring of 2002 by Intel Research and UC Berkeley, to monitor themicroclimates in and around Storm Petrel nesting burrows. Thirty two motes were deployed on theisland, each equipped with sensors for temperature, humidity, barometric pressure, and mid-rangeinfrared. The network was designed to have a tiered structure. The motes were grouped into patchesso that data collected in each patch could be relayed via a gateway to a base station, where datalogging was performed. Within one year of monitoring, the system gathered approximately 1

million readings. In 2003, a second generation network, with more than 100 nodes, was alsodeployed.

ENVIORMENTAL MONITORING

Environmental monitoring is another application for WSNs. The vast spaces involved in suchapplications require large volumes of low cost sensor nodes that can be easily dispersed throughoutthe region. For instance, WSNs have been studied for forest re alarm, landscape hooding alarm, soil

moisture monitoring, microclimate and solar radiation mapping, and environmental observation andforecasting in rivers. Researchers at University of West Australia are developing a prototype WSNfor outdoor, ne-grained environmental monitoring of soil water such a network can be used to assistsalinity management strategies, or to monitor irrigated crops, urban irrigation, and water movementin forest soils. In January 2005, a prototype network was built, which included 15 Mica2 nodesintegrated with soil moisture sensors and other gateway and routing nodes. The systemdistinguishes itself by using a reactive data gathering strategy frequent soil moisture readings arecollected during rain, while less frequent readings are collected otherwise. This strategy helpsincrease the system lifetime.


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BLOCK DIAGRAM


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Working and Operation

There are following three sections are present in this kit.

(i) Sensor Unit.(ii) Test points.(iii) Control Unit.(iv) LCD Display

Explanation of each section is given below

(1) Sensor unit : Thermocouple sensor is providing us analog output in voltage range of 0 to 5v.

(2) Test points : Test points are provided on the kit to check the analog output of the sensor. Graphcan also be plotted on the CRO by using this analog output.

(3) Control unit : Analog output of the sensor is given to the ADC through with digital data is providedto the microcontroller through which whatever processing we want to do we can do.

(4) LCD Display : LCD display is used to display the value of temperature of the atmosphere around thethermocouple.


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ADVANCE TECHNOLOGY Page 20hi di

Experiments

EXPERIMENT NO. 1

AIM:- To study and observe the value of temperature of the atmosphere around the thermocouple.

EQUIPMENTS REQUIRED:- Thermocouple trainer kit, Thermocouple sensor.

THEORY:- All the specification and regarding the kit and sensor is given above in the manual. In

the kit sensor is providing the analog output which is working as an input to ADC. ADC is

providing digital output which is used by controller for processing and it will display the value of

temperature of the atmosphere around the thermocouple.

PROCEDURE: -

(i). Power on the main supply of the kit.

(iii). Now insert the thermocouple sensor inside the atmosphere around which temperature youwant

to detect.

(iv). Observe the change in value of temperature on screen.

Result:- You will observe the value of temperature on the screen.

Thermocouple Manual

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