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Table of Contents:

Chapter1: introduction

1.1Project Overview

1.2Project Objective

1.3Project Flow

Chapter2: Wireless sensor networks

2.1 wireless sensor networks

2.2 Key definitions of sensor networks

2.3 applications on wireless sensor networks

2.4 Network topologies

2.4.1 star network (Single Point-to- Multipoint)

2.4.2 Mesh network

2.4.3 Hybrid star Mesh network

2.5 power consideration in wireless sensor networks

Chapter3: Sensors

3.1control sensors

3.2classificationof measurement errors

3.3 type of sensors3.4application

Chapter4: Related work

Chapter5: Design and implementation

4.1 introduction

4.2 theoryofoperation

4.3model

Chapter6: Conclusion and feature work

List of Tables

List of Figures

List of Appendices


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CHAPTER-1 Introduction

Modern wireless sensor networks are made up of a large number of inexpensidevices that are networked via low power wireless communications.

It is the networking capability that fundamentally differentiates a sensor network fro

a mere collection of sensors by enabling cooperation, coordination, and collaborati

among sensor assets. Harvesting advances in the past decade in microelectronicsensing, analog and digital signal processing, wireless communications, a

networking, wireless sensor network technology is expected to have a significa

impact on our lives in the twenty-first century. Proposed applications of sens

networks include environmental monitoring, natural disaster prediction and reli

homeland security, healthcare, manufacturing, transportation, and home appliances aentertainment. Sensor networks are expected to be a crucial part in future milita

mission, for example, as embodied in the concepts of network centric warfare an

network-enabled capability.

Wireless sensor networks differ fundamentally from general data networks such as t

internet, and as such they require the adoption of a different design paradigm . Oftsensor networks are application specific; they are designed and deployed for speci

purposes. Thus the network design must take into account the specific intend

applications. More fundamentally, in the context of wireless sensor networks, t

broadcast nature of the medium must be taken into account. For battery-operat

sensors, energy conservation is one of the most important design parameters, sin

replacing batteries may be difficult or impossible in many applications. Thus sens

network designs must be optimized to extend the network lifetime. The energy a

bandwidth constraints and the potential large-scale deployment pose challenges

efficient resource allocation and sensor management. A general class of approachescross-layer designs has emerged to address these challenges. In addition, a rethinki

of the protocol stack itself is necessary so as to overcome some of the complexities a

unwanted consequences associated with cross-layer designs.

This edited book focuses on theoretical aspects of wireless sensor networks, aiming provide signal processing and communication perspectives on the design of large-sca

sensor networks. Emphasis is on the fundamental properties of large-scale sens

networks, distributed signal processing and communication algorithms, and nov

cross-layer design paradigms for sensor networking. The design of a sensor netwo

requires the fusion of ideas from several disciplines. Of particular importance are t


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theories and techniques of distributed signal processing, recent advances

collaborative communications, and methodologies of cross-layer design.

This book elucidates key issues and challenges, and the state-of-the-art theories an

techniques for the design of large-scale wireless sensor networks. For the sign

processing and communications research community, the book provides ideas a

illustrations of the application of classical theories and methods in an emerging field applications. For researchers and practitioners in wireless sensor networks, this bo

complements existing texts with the infusion of analytical tools that will play importaroles in the design of future application-specific wireless sensor networks. For studen

at senior and the graduate levels, this book identifies research directions and provid

tutorials and bibliographies to facilitate further investigations [1].The book is divided into 4 chapters :


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Chapter-2 Wireless sensor networks

2.1 Wireless sensor networks

Recent technological advances allow us to envision a future where large numbers of

low-power, inexpensive sensor devices are densely embedded in the physical

environment, operating together in a wireless network. The envisioned applications

of these wireless sensor networks range widely: ecological habitat monitoring

structure health monitoring , environmental contaminant detection industrial process

control , and military target tracking , among others.

A US National Research Council report titled Embedded Everywhere notes that the

use of such networks throughout society could well dwarf previous milestones in

the information revolution. Wireless sensor networks provides bridges between the

virtual world of information technology and the real physical world. They present a

fundamental paradigm shift from traditional inter-human personal communications to

autonomous inter-device communications. They promise unprecedented new abilities

to observe and understand large-scale . real-world phenomena at a fine spatio-

temporal resolution. As a result , wireless sensor networks also have the potential to

engender a new breakthrough scientific advances .

While the notion of networking distributed sensors and their use in military andindustrial applications dates back at least to the 1970s , the early systems where

primarily wired and small in scale . it was only in the 1990s when wireless

technologies and low-power VLSI design became feasible that researchers began

envisioning and investigating large-scale embedded wireless sensor networks for

dense sensing applications.

Figure 1 : A Berkeley mote (MICAz MPR2400 series)


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Perhaps one of the earliest research efforts in the direction was the low-power

wireless integrated micro sensors (LWIM) project at UCLA funded by DARPA . the

LWIM project focused on developing devices with low-power electronics in order to

enable large, dense wireless sensor networks. This project were succeeded by the

Wireless Integrated Networked Sensors (WINS) project a few years later , in which

researchers at UCLA collaborated withR

ockwell science center to develop some ofthe first wireless sensor devices. Other early project in this area, starting around

1999-2000. Were also primarily in academia, at several places included MIT,

Berkeley and USC [2].

Researchers at Berkeley developed embedded wireless sensor networking devices

called motes which were made publicly available commercially, along with TinyOS,

an associated embedded operating system that facilitates the uses of these devices

figure (1) shows the image of Berkeley mote devices the availability of these devicesas an easily programmable , fully functional , relatively inexpensive platform for

experimentation and real deployment has played a significant role in the ongoing

wireless sensor networks revolution

2.2 key definitions of sensor networks

Sensor networks is an interdisciplinary research area that draws on Contributions

from signal processing, networking and protocols, databases and informationmanagement, distributed algorithms, and embedded systems and architecture. In the

following, we define a number of key terms and concepts that will be used

throughout the report as we develop techniques and examples for sensor networks. Sensor: A transducer that converts a physical phenomenon such as heat, light,

sound, or motion into electrical or other signals that may be further manipulated by

other apparatus.

Sensor node: A basic unit in a sensor network, with on-board sensors, processor,

memory, wireless modem, and power supply. It is often abbreviated as node. When a

node has only a single sensor on board, the node is sometimes also referred to as a

sensor, creating some confusion.

Network topology: A connectivity graph where nodes are sensor nodes and edges

are communication links. In a wireless network, the link represents a one-hopconnection, and the neighbors of a node are those within the radio range of the node.


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Detection: The process of discovering the existence of a physical phenomenon. A

threshold-based detector may flag a detection whenever the signature of a physical

phenomenon is determined to be significant enough compared with the threshold.

Classification: The assignment of class labels to a set of physical phenomena being

observed.

Resource: Resources include sensors, communication links, processors, on-board

memory, and node energy reserves.Resource allocation assigns resources to taskstypically optimizing some performance objective.

Sensor tasking: The assignment of sensors to a particular task and the control ofsensor state (e.g., on/off, pan/tilt) for accomplishing the task.

Node services: Services such as time synchronization and node localization that

enable applications to discover properties of a node and the nodes to organizethemselves into a useful network.

Data storage: Sensor information is stored, indexed, and accessed by applications

Storage may be local to the node where the data is generated, load-balanced across anetwork, or anchored at a few points (warehouses).

Embedded operating system (OS): The run-time system support for sensor networkapplications. An embedded OS typically provides an abstraction of system resources

and a set of utilities [3].

2.3 applications on wireless sensor network

A sensor network is designed to perform a set of high-level information processing

tasks[3] such as industrial control and monitoring; home automation and consumer

electronics; security and military sensing; asset tracking and supply chainmanagement; intelligent agriculture; and health monitoring

2.3.1 Industrial Control and Monitoring

A large, industrial facility typically has a relatively small control room, surrounded

by a relatively large physical plant. The control room has indicators and displays that

describe the state of the plant (the state of valves, the condition of equipment, thetemperature and pressure of stored materials, etc.), as well as input devices that

control actuators in the physical plant (valves, heaters, etc.) that affect the observed

state of the plant. The sensors describing the state of the physical plant, their displays

in the control room, the control input devices, and the actuators in the plant are often

all relatively inexpensive when compared with the cost of the armored cable that

must be used to communicate between them in a wired installation. Significant cost


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savings may be achieved if an inexpensive wireless means were available to provide

this communication. Because the information being communicated is state

information, it often changes slowly. Thus, in normal operation, the required data

throughput of the network is relatively low, but the required reliability of the network

is very high. A wireless sensor network of many nodes, providing multiple message

routing paths of multihop communication, can meet these requirements[4].

An example of wireless industrial control is the control of commercial lighting. Muchof the expense in the installation of lights in a large building concerns the control of

the lights where the wired switches will be, which lights will be turned on and off

together, dimming of the lights, etc. A flexible wireless system can employ ahandheld controller that can be programmed to control a large number of lights in a

nearly infinite variety of ways, while still providing the security needed by a

commercial installation.

A further example is the use of wireless sensor networks for industrial safetyapplications. Wireless sensor networks may employ sensors to detect the presence of

noxious, poisonous, or otherwise dangerous materials, providing early detection andidentification of leaks or spills of chemicals or biological agents before serious

damage can result (and before the material can reach the public). Because the

wireless networks may employ distributed routing algorithms, have multiple routingpaths, and can be self-healing and self-maintaining, they can be resilient in the face

of an explosion or other damage to the industrial plant, providing officials with

critical plant status information under very difficult conditions.

The monitoring and control of rotating or otherwise moving machinery is another

area suitable for wireless sensor networks. In such applications, wired sensor and

actuators are often impractical, yet it may be important to monitor the temperature,

vibration, lubrication flow, etc. of the rotating components of the machine tooptimize the time between maintenance periods, when the machine must be taken

off-line. To do this, it is important that the wireless sensor system be capable of

operating for the full interval between maintenance periods; to do otherwise defeats

the purpose of the sensors. This, in turn, requires the use of a wireless sensor networkwith very low energy requirements. The sensor node often must be physically small

and inexpensive as well. Wireless sensor networks may be of particular use in theprediction of component failure for aircraft, where these attributes may be used to

particular advantage.[12]


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Still another application in this area for wireless sensor networks is the heating,

ventilating, and air conditioning (HVAC) of buildings.HVAC systems are typically

controlled by a small number of strategically located thermostats and humidistats

The number of these thermostats and humidistats is limited, however, by the costs

associated with their wired connection to the rest of the HVAC system. In addition

the air handlers and dampers that directly control the room environment are also

wired; for the same reasons, their numbers are also limited.

The heat load generated by people in a building is quite dynamic, however. Diurnal

hebdomadal, seasonal, and annual variations occur. These variations are associated

with the distribution of people in the building throughout the day, week, season, andyear; important changes also affect the heat load of the building at more irregular

intervals. For example, when organizations reorganize and remodel, space previously

used for offices may be used by heat-generating laboratory or manufacturing

equipment. Changes to the building itself must also be considered: interior walls may

be inserted, moved, or removed; windows, curtains, and awnings may be added orremoved, etc. Due to all these possible variations and, as nearly anyone who works in

an office building can attest, improvement is needed.

The root cause of such unsatisfactory HVAC function is that the control system lacks

sufficient information about the environment in the building to maintain acomfortable environment for all. Because they do not require the expense of wired

sensors and actuators, wireless sensor networks may be employed to greatly increase

the information about the building environment available to the HVAC controlsystem, and to greatly decrease the granularity of its response. Wireless thermostats

and humidistats may be placed in several places around each room to provide

detailed information to the control system. Similarly, wireless bypass dampers and

volume dampers can be used in great number to fine-tune the response of the HVAC

system to any situation. Should everyone in an office area move to the conference

room for a meeting, for example, the system can respond by closing the volumedampers in the office area, while opening the volume dampers in the conference

room. Should the group leave the building, the HVAC system may instruct the

wireless bypass dampers to respond to the change in total building heat load. Shouldthe group return during a driving rainstorm, the humidistat in the umbrella and coat

closet could detect the increased humidity in that closet. The HVAC system could

then place especially dry air there, without affecting the occupants elsewhere in thebuilding.


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The wireless HVAC system can also solve one of the great problems facing the

HVAC engineer: balancing heating and air conditioning. It is often the case that heat

sources are not uniformly distributed throughout a building. In the home, for

example, kitchens tend to be warm, due to the heat of cooking, while bedrooms tend

to be cool. In winter, more heated air needs to be sent to the bedroom, where it is

cooler, and less heated air needs to be sent to the kitchen, where it is warmer. In

summer, however, just the opposite is true more cooled air needs to be sent to thekitchen, where it is warmer, and less cooled air needs to be sent to the bedroom,

where it is cooler. This difference between the air distribution of heating and airconditioning is a difficult and expensive problem to solve with wired control

systems, because a volume damper to each room in the house must be independently

controlled. Often, the dampers are placed in a single, fixed position, leaving someareas perpetually cold and others perpetually warm. With wireless sensors and

actuators in the HVAC system, however, the problem becomes trivial; the damper(s)

to each room can be controlled by the sensor(s) in each room, leading to perfectsystem balance at any time of the year.

Such a wireless HVAC system has other advantages. Close monitoring of system

performance enables problems to be identified and corrected before occupancomplaints arise. In addition to the living-area sensors, wireless sensors may be

placed inside air ducts (to monitor the performance of heat exchange apparatus, for

example) without requiring maintenance personnel to make manual measurementsatop ladders. In addition, sensors may be placed in attics and crawlspaces that contain

ductwork; anomalous temperatures in such areas may indicate costly leaks of heatedor cooled air. For these reasons, total building HVAC costs should drop, while

occupant comfort would increase when wireless sensors and actuators are employed.

2.3.2 Home Automation and Consumer Electronics

The home is a very large application space for wireless sensor networks.[13]

Many of

the industrial applications just described have parallels in the home. For example, a

home HVAC system equipped with wireless thermostats and dampers can keep therooms on the sunny side of the house comfortable without chilling the occupants

on the shady side of the house more effectively than a home equipped with only asingle, wired thermostat.However, many other opportunities are available.

One application is the "universal" remote control, a personal digital assistant (PDA)-

type device that can control not only the television, DVD player, stereo, and other


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home electronic equipment, but the lights, curtains, and locks that are also equipped

with a wireless sensor network connection. With the universal remote control, one

may control the house from the comfort of one's armchair. Its most intriguing

potential, however, comes from the combination of multiple services, such as having

the curtains close automatically when the television is turned on, or perhaps

automatically muting the home entertainment system when a call is received on the

telephone or the doorbell rings. With the scale and personal computer both connectedvia a wireless sensor network, one's weight may be automatically recorded without

the need for manual intervention (and the possibility of stretching the truth "just thisonce").

A major use of wireless sensor networks in the home is expected to be for personal

computer peripherals, such as wireless keyboards and mice. Such applications take

advantage of the low cost and low power consumption that are the sine qua non of

wireless sensor networks. Another application in the home is sensor-based

information appliances that transparently interact and work symbiotically together aswell as with the home occupant. These networks are an extension of the information

appliances proposed by Norman.

Toys represent another large market for wireless sensor networks. The list of toys

that can be enhanced or enabled by wireless sensor networks is limited only by one'simagination, and range from conventional radio-controlled cars and boats to

computer games employing wireless joysticks and controllers. A particularly

intriguing field is personal computer (PC)-enhanced toys, which employ thecomputing power of a nearby computer to enrich the behavior of the toy itself. For

example, speech recognition and synthesis may be performed by placing the

microphone and speaker in the toy, along with the appropriate analog-to-digital and

digital-to-analog converters, but employing a wireless connection to the computer,

which performs the recognition and synthesis functions. By not placing the relatively

expensive yet limited speech recognition and synthesis circuits in the toy, and usingthe (much more powerful) computing power already present in the computer, the cost

of the toy may be significantly reduced, while greatly improving the capabilities and

performance of the toy. It is also possible to give the toy complex behavior that is notpractical to implement in other technologies [4].

Another major home application is an extension of the Remote Keyless Entry (RKE)

feature found on many automobiles. With wireless sensor networks, wireless locks,

door and window sensors, and wireless light controls, the homeowner may have a


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device similar to a key fob with a button. When this button is pressed, the device

locks all the doors and windows in the home, turns off most indoor lights (save a few

night lights), turns on outdoor security lights, and sets the home's HVAC system to

nighttime (sleeping) mode. The user receives a reassuring "beep" once this is all done

successfully, and sleeps soundly, knowing that the home is secure. Should a door be

left open, or some other problem exists, a small display on the device indicates the

source of the trouble. The network may even employ a full home security system todetect a broken window or other trouble.

Outside of the home, the location-aware capabilities of wireless sensor networks are

suitable for a diverse collection of consumer-related activities, including tourism[17

and shopping.[18]

,[19]

In these applications, location can be used to provide context-

specific information to the consumer. In the case of the tourism guide, the user is

provided only information relevant to his present view; in the case of the shopping

guide, the user is provided information relevant to the products before him, including

sale items and special discounts and offers.

2.3.3 Security and Military Sensing

The wireless security system described above for the home can be augmented for use

in industrial security applications. Such systems, employing proprietary

communication protocols, have existed for several years. They can support multiplesensors relevant to industrial security, including passive infrared, magnetic door

opening, smoke, and broken glass sensors, and sensors for direct human intervention(the "panic button" sensor requesting immediate assistance).

As with many technologies, some of the earliest proposed uses of wireless sensor

networks were for military applications. One of the great benefits of using wireless

sensor networks is that they can be used to replace guards and sentries around

defensive perimeters, keeping soldiers out of harm's way. In this way, they can serve

the same function as antipersonnel mines, without the attendant hazard mines

represent to allied personnel during the battle (or the civilian population afterward)

In addition to such defensive applications, deployed wireless sensor networks can beused to locate and identify targets for potential attack, and to support the attack by

locating friendly troops and unmanned vehicles. They may be equipped with acoustic

microphones, seismic vibration sensors, magnetic sensors, ultra wideband radar, andother sensors.

[22]


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Wireless sensor networks can be small, unobtrusive, and camouflaged to resemble

native rock, trees, or even roadside litter. By their nature, multihop networks are

redundant. These networks have distributed control and routing algorithms (i.e.

without a single point of failure), a feature that makes them difficult to destroy in

battle.[23]

The use of spread spectrum techniques, combined with the bursty

transmission format common to many wireless sensor networks (to optimize battery

life), can give them a low probability of detection by electronic means. The relativelocation determination capability of many ad hoc wireless sensor networks can

enable the network nodes to be used as elements of a retro directive arrayof

randomly distributed radiating elements; such an array can be used to provide

exfiltration of the sensor network data. [4]The relative location information is used to

align the relative carrier phase of the signals transmitted by each node; with thisinformation, the exfiltrated data may be transmitted not just in the direction of the

incoming signal, but in any desired direction. Beam forming techniques can also be

applied to the sensors themselves, to enhance their sensitivity and improve detectionprobabilities.

Wireless sensor networks can also be effective in the monitoring and control of

civilian populations with the use of optical, audio, chemical, biological, andradiological sensors to track individuals and groups. The control of wireless sensor

networks and the data they produce in a free society, while an important public

policy discussion,[28]

is outside the scope of this text.

2.3.4 Asset Tracking and Supply Chain Management

A very large unit volume application of wireless sensor networks is expected to be

asset tracking and supply chain management. Asset tracking can take many forms

One example is the tracking of shipping containers in a large port. Such port facilities

may have tens of thousands of containers, some of which are empty and in storage,

while others are bound for many different destinations. The containers are stacked,

both on land and on ship. An important factor in the shipper's productivity (and

profitability) is how efficiently the containers can be organized so that they can behandled the fewest number of times and with the fewest errors. For example, it is

important that the containers next needed be on top of a nearby stack instead of at thebottom of a stack1 km away. An error in the location record of any container can be

disastrous; a "lost" container can be found only by an exhaustive search of a very

large facility. Wireless sensor networks can be used to advantage in such a situation;by placing sensors on each container, its location can always be determined.


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Similar situations involving large numbers of items that must be tracked occur in rail

yards, where thousands of railroad cars of all types must be organized, and in the

manufacture of durable goods, such as cars and trucks, that may sit in large lots or

warehouses after manufacture, but before delivery to a retailer.

A related application is that of supply chain management. An item in a large

warehouse, but with its precise location unknown, is practically lost because it isunavailable to be used or sold. This represents inventory shrinkage, even though theitem is physically on the premises, and is therefore a business expense. In a manner

similar to that of the asset tracking application described previously, wireless sensor

networks can be used to reduce this cost; however, additional benefits may beobtained. In a large distribution chain, one of the most vexing problems facing the

distributor is to quickly and accurately identify the location of material to be sold

Knowing where a product is can mean the difference between making or not making

a sale, but knowing the status of the entire supply chain from raw materials

through components to final product can help a business operate more efficientlyFor example, transferring excess product from Division X (where it is selling slowly)

to Division Y (where it is selling briskly) can help a company avoid the purchase of

component parts to manufacture more product for Division Y. Wireless sensornetworks placed along the supply chain enable everyone in the business to make

better decisions because more information about product in the supply chain i

available.

This information can also be used as a competitive advantage; by being able to tell acustomer exactly where his product is (or even where the component parts of his

product are) in the supply chain, the customer's confidence of on-time delivery (and

opinion of the seller's competence) rises. This has already been used extensively in

the package shipping industry, so much so that customers expect this service as a

matter of course a shipper that cannot tell a customer where his package is at any

given time is rarely reused [4].

The use of wireless sensor networks for the tracking of nuclear materials has already

been demonstrated in the Authenticated Tracking and Monitoring System (ATMS)The ATMS employs wireless sensors (including the state of the door seal, as well as

infrared, smoke, radiation, and temperature sensors) within a shipping container (e.g.,a railroad car) to monitor the state of its contents. Notification of sensor events are

wirelessly transmitted within the shipping container to a mobile processing unit,

connected to both a Global Positioning System (GPS) receiver and an International


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Maritime Satellite (INMARSAT) transceiver. Through the INMARSAT system, the

location and status of each shipment may be monitored anywhere in the world.

2.3.5 Intelligent Agriculture and Environmental Sensing

A textbook example of the use of wireless sensor networks in agriculture is the rain

gauge. Large farms and ranches may cover several square miles, and they mayreceive rain only sporadically and only on some portions of the farm. Irrigation isexpensive, so it is important to know which fields have received rain, so that

irrigation may be omitted, and which fields have not and must be irrigated. Such an

application is ideal for wireless sensor networks. The amount of data sent over thenetwork can be very low (as low as one bit "yes or no" in response to the "Did

it rain today?" query), and the message latency can be on the order of minutes. Yet

costs must be low, and power consumption must be low enough for the entirenetwork to last an entire growing season.

The wireless sensor network is capable of much more than just soil moisture

measurements, however, because the network can be fitted with a near-infinite

variety of chemical and biological sensors. The data that is provided by such anetwork is capable of providing the farmer with a graphical view of soil moisture;

temperature; the need for pesticides, herbicides, and fertilizers; received sunshine;

and many other quantities. This type of application is especially important invineyards, where subtle environmental changes may have large effects on the value

of the crop and how it is processed.

The location determination features of many wireless sensor networks also may be

used in advanced control systems to enable more automation of farming equipment

[4].

Many applications of wireless sensor networks are also used on ranches.Ranchers

may use wireless sensor networks in the location determination of animals within the

ranch and, with sensors placed on each animal, determine the need for treatments to

prevent parasites. Dairy farmers may use wireless sensors to determine the onset ofestrus in cattle, a labor-intensive manual process at present.Hog and chicken farmers

typically have many animals in cooled, ventilated barns. Should the temperature riseexcessively, many thousands of animals may be lost. Wireless sensor networks can

be used to monitor the temperature throughout the barn, keeping the animals safe.


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Wireless sensor networks may also be used for low-power sensing of environmental

contaminants such as mercury.[31]

Integrated micro cantilever sensors sensitive to

particular contaminants can achieve parts-per-trillion sensitivities. These micro-

electromechanical (MEMS) sensors may be integrated with a wireless transceiver in

a standard complementary metal oxide semiconductor (CMOS) process, providing a

very low-cost solution to the monitoring of chemical and biological agents.

2.3.6 Health Monitoring

A market for wireless sensor networks that is expected to grow quickly is the field of

health monitoring. "Health monitoring" is usually defined as "monitoring of non-life-critical health information," to differentiate it from medical telemetry, although the

definition is broad and nonspecific, and some medical telemetry applications can be

considered for wireless sensor networks.

Two general classes of health monitoring applications are available for wirelesssensor networks. One class is athletic performance monitoring, for example, tracking

one's pulse and respiration rate via wearable sensors and sending the information to a

personal computer for later analysis.[32]

The other class is at-home health monitoringfor example, personal weight management.

[33]The patient's weight may be wirelessly

sent to a personal computer for storage. Other examples are daily blood sugar

monitoring and recording by a diabetic, and remote monitoring of patients withchronic disorders.

[34]

The use of wireless sensor networks in health monitoring is expected to accelerate

due to the development of biological sensors compatible with conventional CMOS

integrated circuit processes.[35]

These sensors, which can detect enzymes, nucleic

acids, and other biologically important materials, can be very small and inexpensive,

leading to many applications in pharmaceuticals and medical care.

A developing field in the health monitoring market is that of implanted medical

devices. In the United States, the Federal Communications Commission (FCC)

established regulations governing the Medical Implant Communications Service, inJanuary 2000, "for transmitting data in support of diagnostic or therapeutic functions

associated with implanted medical devices."[36]

These types of systems can be usedfor a number of purposes, from monitoring cardiac pacemakers to specialized drug

delivery systems.


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consumption to a minimum. It also allows for low latency communications between

the remote node and the base station. The disadvantage of such a network is that the

base station must be within radio transmission range of all the individual nodes and is

not as robust as other networks due to its dependency on a single node to manage the

network.

Figure 2

2.4.2Mesh network

A mesh network allows for any node in the network to transmit to any other node inthe network that is within its radio transmission range. This allows for what is known

as multihop communications; that is, if a node wants to send a message to another

node that is out of radio communications range, it can use an intermediate node to

forward the message to the desired node. This network topology has the advantage of

redundancy and scalability.

If an individual node fails, a remote node still can communicate to any other node in

its range, which in turn, can forward the message to the desired location. In additionthe range of the network is not necessarily limited by the range in between single

nodes, it can simply be extended by adding more nodes to the system . The

disadvantage of this type of network is in power consumption for the nodes that

implement the multihop communications are generally higher than for the nodes that

dont have this capability, often limiting the battery life. Additionally, as the number


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of communication hops to a destination increases, the time to deliver the message

also increases, especially if low power operation of the nodes is a requirement.

Figure 3

2.4.3 hybrid star Mesh network

A hybrid between the star and mesh network provides for a robust and versatile

communications network, while maintaining the ability to keep the wireless sensor

nodes power consumption to a minimum. In this network topology, the lowest power

sensor nodes are not enabled with the ability to forward messages. This allows for

minimal power consumption to be maintained.However, other nodes on the network

are enabled with multihop capability, allowing them to forward messages from the

low power nodes to other nodes on the network. Generally, the nodes with the

multihop capability are higher power, and if possible, are often plugged into the

electrical mains line. This is the topology implemented by the up and coming meshnetworking standard known as ZigBee


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Figure 4

2.5power consideration in wireless sensor networks

The single most important consideration for a wireless sensor network is power

consumption. While the concept of wireless sensor networks looks practical and

exciting on paper, if batteries are going to have to be changed constantly, widespread

adoption will not occur. Therefore, when the sensor node Is designed power

consumption must be minimized.

contributors to power consumption in a typical 5000-ohm wireless strain gage sensor

node versus transmitted data update rate. Note that by far, the largest power

consumption is attributable to the radiolink itself.


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Figure 5


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Chapter- 3 Sensors

Sensors are devices that convert a physical parameter such as room temperature

blood pressure or wind speed into a signal that can be measured electrically. Other

sensor outputs are equally valid (e.g. visual output from a glass thermometer), but wewill confined our coverage to electrical output sensors as they are more compatible

with electronic measuring devices.

Once the physical parameter has been converted to an electrical equivalent it is easily

input into a computer or microprocessor for manipulating, analyzing and displaying.

By far the most common parameter measured is temperature. At present temperature

is the only parameter covered in detail [5].

Each year hundreds millions of sensors are manufactured. They are in domestic

appliances, medical equipment, industrial control systems, air-conditioning systems,aircraft, satellites and toys. Sensors are becoming smarter, more accurate andcheaper. They will play an ever increasing role in just about every field imaginable.


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Figure 6

3.1 control sensorsA sensor as a control component is to capture correctly and speedy data of anenvironment where a machine is installed and data of products that are being

processed, and then convert those data to controllable electric signals or information

that human can easily confirm.


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(1) Role of sensor in automation Flow of control:

Figure 7

Figure 8


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Application in Factory

Figure 9

(2) Type of sensor


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(3) Use of sensor

(4) Sensor Output

ON/OFF Output

ON /OFF when input value exceeds the value set (it may be Called High/Low, 1/0)

Digital Sensor input

Which changes itself continuously is output as digital value such as BCD/BIN.

Analog Sensor input

Which changes itself continuously is output as consecutive value of voltage /electriccurrent.

3.2 Classification of measurement errorsA good sensor obeys the following rules:

Is sensitive to the measured property

Is insensitive to any other property

Does not influence the measured property

Ideal sensors are designed to be linear. The output signal of such a sensor is linearly

proportional to the value of the measured property. The sensitivity is then defined as

the ratio between output signal and measured property. For example, if a sensor

measures temperature and has a voltage output, the sensitivity is a constant with the

unit [V/K]; this sensor is linear because the ratio is constant at all points of

measurement.


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Sensor deviations

If the sensor is not ideal, several types of deviations can be observed:

The sensitivity may in practice differ from the value specified. This is called a

sensitivity error, but the sensor is still linear.

Since the range of the output signal is always limited, the output signal will

eventually reach a minimum or maximum when the measured property exceedsthe limits. The full scale range defines the maximum and minimum values of the

measured property.

If the output signal is not zero when the measured property is zero, the sensor has

an offset or bias. This is defined as the output of the sensor at zero input.

If the sensitivity is not constant over the range of the sensor, this is

called nonlinearity. Usually this is defined by the amount the output differs from

ideal behavior over the full range of the sensor, often noted as a percentage of the

full range. If the deviation is caused by a rapid change of the measured property over time,

there is a dynamic error. Often, this behavior is described with a bode

plot showing sensitivity error and phase shift as function of the frequency of a

periodic input signal.

If the output signal slowly changes independent of the measured property, this is

defined as drift (telecommunication).

Long term drift usually indicates a slow degradation of sensor properties over a

long period of time. Noise is a random deviation of the signal that varies in time.

Hysteresis is an error caused by when the measured property reverses direction,but there is some finite lag in time for the sensor to respond, creating a different

offset error in one direction than in the other.

If the sensor has a digital output, the output is essentially an approximation of the

measured property. The approximation error is also called digitization error.

If the signal is monitored digitally, limitation of the sampling frequency also can

cause a dynamic error. The sensor may to some extent be sensitive to properties other than the property

being measured. For example, most sensors are influenced by the temperature of

their environment.

All these deviations can be classified as systematic errors or random errors

Systematic errors can sometimes be compensated for by means of some kind


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of calibration strategy. Noise is a random error that can be reduced by signal

processing, such as filtering, usually at the expense of the dynamic behavior of the

sensor.

Resolution

The resolution of a sensor is the smallest change it can detect in the quantity that it ismeasuring. Often in a digital display, the least significant digit will fluctuate,

indicating that changes of that magnitude are only just resolved. The resolution is

related to the precision with which the measurement is made. For example,

a scanning tunneling probe (a fine tip near a surface collects an electron tunneling

current) can resolve atoms and molecules.

3.3 Types of sensorsSensors are used to measure basic physical phenomena including:

1. Acceleration - Shock & Vibration.

2. Angular / Linear Position

3.Chemical/Gas Concentration

4. Humidity

5. Flow Rate

6. Force

7. Magnetic Fields8. Pressure

9. Sound

10.Temperature

11..Velocity

y Sensors: Acceleration

An accelerometer is an electromechanical transducer which produces at its outputterminals, a voltage or charge that is proportional to the acceleration to which it issubjected. The piezoelectric elements (similar to small crystals) within the

accelerometer have the property of producing an electrical charge which is directly

proportional to the strain and thus the applied force when loaded either in tensioncompression or shear.


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Applications include measurement of Acceleration, Angular Acceleration, Velocity,

Position, RPM or AngularRate, Frequency, Impulse and Impulse Energy, Force, Tilt

and Orientation, and Motion Detection.

y Sensors: Linear / Angular Position

Potentiometers

Potentiometers utilize a variable resistor to convert an angle or displacement to

a resistance/voltage. They operate by moving a contact along a resistor to

produce a voltage proportional to the position.

Encoders

An encoder is a sensor of mechanical motion. It translates motion

(such as position, velocity, and acceleration) into electrical signals.

Absolute encoders have a unique value for each mechanical

position and thus the position is known "absolutely". With this type

of encoder, the position information is never lost and is instantlyavailable as a digital word on power-up.

Incremental encoders have output signals which repeat over the range of motion and

thus each mechanical position is not uniquely defined. The current position sensed is

only incremental from the last position sensed. Thus at power up, the position of anincremental encoder is not known since the output signals are not unique to any

singular position. They are made up of2 major parts, the disk and the sensor. The

disk of an incremental encoder is patterned with a single track of lines near the

outside edge of the disk. The disk count is defined as the number of dark/light line

pairs that occur per revolution (CPR). As a rule, one or more tracks are added to

generate a signal that occurs once per revolution (index signal), which can be used to

indicate zero or home on the encoder. Count and direction information can be

obtained from both absolute and incremental encoders.

Rotary Encoder

Figure 10


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y Sensors: Chemical / Gas Concentrations

Chemical / Gas Concentrations

There are many different types of sensors for detection

concentration levels of chemicals and gasses. These sensors

are critical for safety considerations in many industrialapplications.

Following is a table providing a brief summary of sensor types and applications.

Table 3y Sensors: Humidity

Humidity sensors are used to measure the humidity in air, as a fraction of the

maximum amount of water that can be absorbed by air at a certain temperature

Under normal atmospheric conditions and a given temperature this fraction can varybetween 0 ( absolute dry point ) and 100 (Condensation starting point ). This relative

Catalytic Sensor

Figure 11


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humidity measurement is only valid under the above mentioned temperature and

atmospheric conditions, thus making very important the fact that the sensor must not

be affected by temperature or pressure changes. As a result it is obvious that

Temperature or Pressure Dependent sensing elements, such as Mechanical Devices

and Resistive type Sensors, are far behind of the respective non-dependent ones, such

as Capacitance sensors. Absorption based humidity sensors provide both temperature

and %RH (Relative Humidity) outputs.

Humidity Cells are mainly Capacitance sensors characterized of an excellent long

term stability, good resistance to pollutants, precise measurements, high sensitivity,

intergangeability and wettability.

Applications Include:

1.Refrigeration

2.Drying Processes3.Meteorology4.Battery-powered systems5.OEM assemblies

y Sensors: Flow Rate

Flow Rate

Ventura Valves

A Ventura valve reduces the cross section of a pipe to create a

pressure differential from the normal pipe diameter. The pressure

differential increases with the velocity of the flow to aid in

determining the flow rate.

Transit-Time Flow Measurement Principle

A transit-time flow meter measures the effect of a liquid's flow

velocity on bi-directional acoustical signals. An upstream

transducer (T1) sends a signal to a downstream transducer (T2)that in turn sends a signal back. When there is no flow, the time to go from the T1 to

T2 is the same as the time going from T2 to T1.However, when there is flow, the

Flow Rate Sensor

Figure 12

Figure 13


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effect of the liquid's flow velocity on the acoustical signal is to assist the signal in the

up to downstream direction and hinder the signal in the down to upstream direction

This creates the time difference by which the liquid's flow velocity, and ultimately

the flow rate, is determined.

Pitot Tubes

Pitot tubes have been used in flow measurement for years. Conventional pitot tubes

sense velocity pressure at only one point in the flowing stream. Therefore, a series of

measurements must be taken across the stream to obtain a meaningful average flowrate.

Flow Transducers

Fluid flowing through the sensor spins a magnetic rotor to induce a voltage in a

coil. An electronic circuit measures the frequency of the electrical pulsesgenerated and computes the flow rate. This rate is converted to a 0-5 VDC or0-20 MA output proportional to the flow rate and also used to control a relay. The

relay trip point may be present at the factory or adjusted by the user by turninga potentiometer.

y Sensors: Force

Force

Load Cells / Force Transducers

Load Cells are intended for determination of static or dynamictensile and compressive loads and come in many different forms

including compression, tension, simple beam and single point.

Force transducers can be used as load cells, but can also be used in

weighing applications and measuring compression or tension.

Load cells can be built utilizing either transducers, LVDTs, strain

gauges or piezoelectric sensors. Tension Load CellFigure 14


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Strain Gauges

Strain gauges are used for the measurement of tensile and

compressive strain in a body and can therefore pick up

expansion as well as contraction. Strain is caused in a body

by internal or external forces, pressures, moments, heat, or

structural changes in the material. In general, most types ofstrain gages depend on the proportional variance of electricalresistance to strain: the piezoresistive or semi-conductor gage,

the carbon-resistive gage, the bonded metallic wire, and foil

resistance gages.

The bonded resistance strain gage is by far the most widely

used in experimental stress analysis. They typically consist of a grid of very fine wire

or foil bonded to the backing or carrier matrix. The carrier matrix attaches to test

specimens with an adhesive. When the specimen is mechanically stressed (loaded),the strain on the surface is transmitted to the resistive grid through the adhesive and

carrier layers. The strain is then found by measuring the change in resistance.

The bonded resistance strain gage is low in cost, can be made with a short gagelength, is only moderately affected by temperature changes, has small physical size

and low mass, and has fairly high sensitivity to strain.

y

Sensors: Magnetic FieldsMagnetic Fields

Magneto resistive (MR) Sensors

Magneto resistive sensors can determine the change in earth's magnetic field

due to the presence of a ferromagnetic object or position within the earth's

magnetic field. The high bandwidth allows detection of vehicles and other

ferrous objects at high speeds. The sensors are contactless and the workingdistance is dependent on the ferromagnetic mass it is measuring. Applications

include Compassing and Navigation, Vehicle Detection, Virtual Reality,Laboratory Instrumentation, Medical Instruments, Underground Boring

Equipment and Flux Gate Replacement.

Strain Gauges

Figure 15


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y Sensors: Pressure

Pressure Transducer

Pressure sensor applications include flow (HVAC), height of a

column of liquid, altitude, depth of a submerged object,

position, sound (dbspl), barometric pressure, map, pressuredrop, vacuum, volumetric displacement, and weight.

A transducer is simply a device (or medium) that converts

energy from one form to another. The term is generally applied to devices that takephysical phenomenon (pressure, temperature, humidity, flow, etc.) and convert it to

an electrical signal.

Pressure transducers/sensors use a wide range of operating principles including:

1.Motion transducers use a bellows or Bourdon tube to convert pressure to anoutput. In one common type, the LVDT, an inductive member is driven into orout of a coil. It contains numerous pivots and linkages, making it nonlinear and

susceptible to wear and vibration, but it has the advantage of inherently high

output.2.Pressure potentiometers have characteristics similar to those of LVDTs. In

this case, a wiper is driven across a resistive coil, with output determined bywiper position. Compared to an LVDT, it has the added disadvantage of coil

wear. If continuously operated in about the same pressure range, it may

suddenly short out or produce severely nonlinear output. These sensors are

rather inexpensive.

3.Silicon or "chip" transducers are widely used in high-volume applicationsThere are two types of silicon pressure sensors, capacitive and piezoresistive

Capacitive devices are much more stable, sensitive, and temperature resistant

Piezoresistive types are easier to make and cost less and therefore dominate themarket.

4.Capacitance transducers use a flexing diaphragm to produce capacitancechanges proportional to applied pressure. Because of their low price, a common

application of these devices is in automobiles. One drawback is at normal

Pressure Transducer - Motorola

Figure 16


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The condenser microphones are available in two types: bias type and backelectrets type. The difference is whether the DC voltage is applied from the

outside or permanently electrically polarized polymer film is used in place of

applying voltage. In general, the bias type provides higher sensitivity and

stability.

Sound Intensity Microphones

Sound intensity is a measure of the "flow of energy passing through a unit area per

unit time" and its measurement unit is W/m2. The sound intensity microphone probeis designed to capture sound intensity together with the unit direction of flow as a

vector quantity. This is achieved by incorporating more than one microphone in a

probe to measure the sound energy flow. Conventional microphones can measure

sound pressure (unit: Pa), which represents sound intensity at a specific place (one

point), but can measure the direction of flow. The sound intensity microphone is

therefore used for sound source probing and for measuring sound power.

y Sensors: Temperature

Temperature

Typical applications for temperature sensors include:

y HVAC - room, duct, and refrigerant equipmenty Motors - overload protection

y Electronic circuits - semiconductor protection

y Electronic assemblies - thermal management,

temperature compensation

y Process control - temperature regulation

y Automotive - air and oil temperature

y Appliances - heating and cooling temperature

Sensor Types

1.Thermocouples - Thermocouples are pairs of dissimilar metal alloy wiresjoined at least at one end, which generate a net thermoelectric voltage between

the two ends according to the size of the temperature difference between the

Temperature Sensors

Figure 18


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ends, the relative Seebeck coefficient of the wire pair and the uniformity of the

wire's relative Seebeck coefficient.

2.Thermistors - Thermistors (Resistance Thermometers) are instruments used tomeasure temperature by relating the change in resistance as a function of

temperature.

3.Radiation Pyrometer - A device to measure temperature by sensing the

thermal radiation emitted from the object.4.Radiation Thermometers (Optical Pyrometers and Infrared

Thermometers) - Optical Pyrometers are devices used to measure temperatureof an object at high temperatures by sensing the brightness of an objects

surface.

5.Resistance Temperature Detectors (RTDs) - RTD's (Resistance TemperatureDetectors) are precision, wire-wound resistors with a known temperature

resistance characteristic. In operation, the RTD is usually wired into a specific

type of circuit (Wheatstone bridge). They are nearly linear over a wide rangeof temperatures and can be made small enough to have response times of a

fraction of a second. They require an electrical current to produce a voltagedrop across the sensor that can be then measured by a calibrated read-out

device. The output of this circuit can be used to drive a meter which has been

calibrated in temperature, or to operate a relay to sound an alarm or shut downthe motor. The Platinum RTD is the most accurate and stable temperature

detector from zero to about 500C. It can measure temperatures up to 800C

The resistance of the RTD changes as a function of absolute temperature, so it

is categorized as one of the absolute temperature devices. (In contrast, thethermocouple cannot measure absolute temperature; it can only measure

relative temperature.)

6.Fiber Optic Temperature Sensors - Optical-based temperature sensors provide accurate and stable remote measurement of on-line temperatures in

hazardous environments and in environments having high ambient

electromagnetic fields without the need for calibration of individual probes and

sensors.

Optical temperature sensor systems measure temperatures from -200C to 600C

safely and accurately even in extremely hazardous, corrosive, and high electro-magnetic field environments. They are ideal for use in these conditions because

their glass-based technology is inherently immune to electrical interference and

corrosion. Since there is no need to recalibrate individual sensors, operator and


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technician safety is greatly enhanced as the need for their repeated exposure to

field conditions is eliminated.

Probes are made from largely non-conducting and low thermal conductance

material, resulting in high stability and low susceptibility to interference, and in

increased operator safety. Optical cables also have a much higher information-

carrying capacity and are far less subject to interference than electricalconductors.

7.Silicon Temperature Sensors - Integrated circuit temperature sensors differsignificantly from the other types in a couple of important ways. The first is

operating temperature range. A temperature sensor IC can operate over the

nominal IC temperature range of -55 C to +150 C. Some devices go beyond

this range while others, because of package or cost constraints, operate over a

narrower range. The second difference is functionality. A silicon temperature

sensor is an integrated circuit, including extensive signal processing circuitrywithin the same package as the sensor.


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y Sensors: Velocity

Velocity

Linear Velocity Transducer - LVT

The LVT is based on the principle of magnetic induction

and provide reliable velocity measurement in a linear

motion. Passing a magnet through the coil form

generates a voltage proportional to the magnets velocity

and field strength. This output signal is used to carefullymonitor component velocities in various applications.

Tachometer

The tachometer measures the angular velocity of arotating shaft using one of two methods. The first type

connects a DC generator (motor) to the shaft whichproduces a voltage proportional to the increase in shaft

angular velocity. The second type utilizes a magnet with

a pickup coil. As the magnet passes the coil a pulse isgenerated. The pulse magnitude and frequency are proportional to the angular

speed.

Figure 19

Handheld Tachometer


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3.4 Applications:

Sensors are used in everyday objects such as touch-sensitive elevator buttons and

lamps which dim or brighten by touching the base. There are also innumerableapplications for sensors of which most people are never aware. Applications include

cars, machines, aerospace, medicine, manufacturing and robotics.

A sensor's sensitivity indicates how much the sensor's output changes when themeasured quantity changes. For instance, if the mercury in a thermometer moves 1

cm when the temperature changes by 1C, the sensitivity is 1 cm/C. Sensors that

measure very small changes must have very high sensitivities. Sensors also have an

impact on what they measure; for instance, a room temperature thermometer inserted

into a hot cup of liquid cools the liquid while the liquid heats the thermometer

Sensors need to be designed to have a small effect on what is measured; making the

sensor smaller often improves this and may introduce other advantages

Technological progress allows more and more sensors to be manufactured on amicro-scopic scale as micro-sensors using MEMS technology. In most cases, amicro-sensor reaches a significantly higher speed and sensitivity compared

with macroscopic approaches.


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Figure 20

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