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University Of Maryland Baltimore County

Faculty Of Engineering Of The University Of Porto

A Sensor Network For An Early And Efficient Leak Detection In Long Pipelines

Alexandre Santos

PROVISIONAL VERSION

Master in Electrical and Computer Engineering Automation Major

Supervisor: Mohamed Younis (PhD) Co-Supervisor: Paulo Portugal (PhD)

January 2011

© Alexandre Santos, 2011

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Abstract

Our society relies on an extensive pipeline network to transfer and deliver water, gas,

oil, etc. In many cases the pipeline extends over hundreds of miles and run through

inhospitable environment. The pipes are often subject to erosion over time due to the

surrounding environment. In addition, pipes carrying valuable commodity may be subject to

theft, sabotage, etc. Leakage not only would waste resources, but also can be harm and

hazardous. Therefore detecting leakage and containing its negative effect is very important.

Current pipeline monitoring systems are inefficient and costly. They lack responsiveness

and often report the problem after significant fluid is spilled. Furthermore, current systems

involve mobile equipment and significant manpower. Sensor networks can be invaluable in

providing a comprehensive, economic and effective solution. This project opts to investigate

the design of a wireless sensor networks that continuously monitor a pipeline and provide an

early warning when leakage is starting.

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Resumo

A nossa sociedade está sustentada sobre uma extensa rede de “pipelines”, quer seja para

a transporte de água, gás ou petróleo.

Em muitos casos, estes “pipelines” estendem-se ao longo de vários quilómetros, passando

por ambientes inóspitos e estando sujeitos a processos de desgaste de forma prolongada.

Além disso, estes “pipelines” transportam muitas vezes matérias primas importantes,

podendo ser alvo de ataques como pilhagens ou sabotagens. As fugas não só desperdiçam

recursos como também podem trazer consequências graves. Nesse sentido, é importante

detectar e controlar os efeitos negativos que uma fuga pode acarretar.

Os sistemas de monitorização existentes actualmente são ineficientes e dispendiosos.

Apresentam falhas nos tempos de resposta aos acontecimentos provocando com frequência

fugas de fluidos em quantidades consideráveis. Além disso, os sistemas actualmente

existentes envolvem equipamentos portáteis o que implica a necessidade de mão-de-obra

para monitorizar os “pipelines”. Por estas razões, a implementação de uma rede de sensores

para a detecção de fugas trás elevados benefícios, fornecendo uma solução abrangente,

eficiente e de baixo custo.

Este projecto pretende assim investigar o desenvolvimento de uma rede de sensores sem-

fio que possibilite uma monitorização de um “pipeline”, fornecendo informações sobre uma

fuga em tempo-real.

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Contents

Chapter 1 ....................................................................................... 12  Introduction ................................................................................................... 12  

1.1   Motivation ........................................................................................... 12  1.2   Objectives ........................................................................................... 13  1.3   Work Plan ............................................................................................ 14  

Chapter 2 ....................................................................................... 15  Flow Measurement ........................................................................................... 15  

2.1   Background .......................................................................................... 15  2.2   Basic Principles ..................................................................................... 16  2.3   Flow Meters ......................................................................................... 22  2.4   Detection Of Leaks ................................................................................. 29  Summary ................................................................................................... 30  

Chapter 3 ....................................................................................... 31  Sensor Networks .............................................................................................. 31  

3.1   Background .......................................................................................... 31  3.2   Application Areas For WSN ........................................................................ 32  3.3   Challenges & Requirements For WSNs ........................................................... 36  3.4.   Energy Scavenging .................................................................................. 37  Summary ................................................................................................... 39  

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List Of Figures

Chapter 1

Figure 1.1 - Property Damage 1990 - 2009 [2] ......................................................... 12  

Figure 1.2 - Thesis work Plan ............................................................................. 14  

Chapter 2

Figure 2.1 - Block diagram of a flow measurement system [7]. .................................... 16  

Figure 2.2 - Laminar Flow versus Turbulent Flow [10] ............................................... 17  

Figure 2.3 - Flow profile of a fluid [12] ................................................................. 18  

Figure 2.4 - Hydraulic condition for pipe flow [9] .................................................... 19  

Figure 2.5 - Electromagnetic flow meter [14] ......................................................... 23  

Figure 2.6 - Ultrasonic flow meter - Doppler [9] ...................................................... 24  

Figure 2.7 - Ultrasonic flow meter - Transit-time [9] ................................................ 24  

Figure 2.8 - Working principle of transit-time flow meter [14] ..................................... 25  

Figure 2.9 – Cross-correlation flow meter [9] .......................................................... 26  

Chapter 3

Figure 3.1- Typical architecture of sensor network and sensor node. Based on [18] ............ 32  

Figure 3.2 - A sensor network for military surveillance application. From [22]. ................. 33  

Figure 3.3 - Enemy target localization and monitoring using WSNs. From [20]. ................. 34  

Figure 3.4 - Forest-fire monitoring application. From [20]. ......................................... 35  

List Of Tables

Chapter 2

Table 2.1 - Comparison of flow meters technologies ................................................. 27  

Table 2.2 - Types of flow meters and its characteristics ............................................ 27  

Chapter 3

Table 3.1 - Comparison of various potential power sources for WSNs. ............................ 38  

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Abbreviations and Symbols

Abbreviation list (alphabetical order)

EMF Electromotive Force

LDS Leak Detection Systems

MPPT Maximum Power Point Tracker

PHMSA U.S. Department of Transportation Pipeline and Hazardous Materials Safety Administration

WSN Wireless Sensor Network

WSNs Wireless Sensor Networks

Symbols list

A Area

Q Volumetric Flow Rate

V Volume

! Velocity

! Mass Density

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Chapter 1

Introduction

1.1 Motivation

Modern economy relies on an extensive network of pipelines for transferring billions of

dollars of crude oil or natural gas. The need to transport these commodities throughout the

world has led to sudden establishment of new pipelines that extends over hundreds of miles

and run through inhospitable environments.

Among the main issues associated with the transport of commodities are leakage

problems. According to the US Department of Transportation Pipeline and Hazardous

Materials Safety Administration (PHMSA), 25% of all pipeline failure incidents reported in the

US from 2002 to 2003 were caused by corrosion (leakage main causes)[1].

In addition, PHMSA’s reports reveal that pipeline incidents cause a significant damage to

property and product losses (Figure 1.1) [2].

Figure 1.1 - Property Damage 1990 - 2009 [2]

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Moreover, leakage not only damage companies property and profits, it also damages its

reputation and most important, people’s lives and the world’s environment. This issue

becomes even more conspicuous in the oil industry case, where leakage can lead to

catastrophic disasters.

 

In the latest oil spill accident, in Gulf Mexico, “…scientists say, the impacts of oil spill are

likely to go far beyond the oiled birds and dead sea turtles, spoiled beaches and wetlands

that we think of when we think ‘oil spill.’ ”

In Newsweek [3]

For this reason, the development of leak detection systems (LDS) is critical in pipeline

networks.

Despite of its importance, current pipeline monitoring systems are inefficient, costly and

they lack responsiveness [4]. Hence, it is important to develop a system capable of detecting

leaks quickly, efficiently and with low operational costs. It is within this context that wireless

sensor networks (WSNs) emerge. The advantage of using this type of networks lies in its

features that provide. This comprehends low deployment cost, low energy consumption and

high communication reliability.

In this project, the literature review on LDS was done having in mind the design of a non-

invasive monitoring system that continuously supervises a pipeline and provides an early

warning when leakage starts to occur.

As regarding to WSN, its literature review was done concerning some technical issues that

affect the network performance as well as the pipeline system requirements.

1.2 Objectives

This thesis aims to develop a pipeline monitoring system to detect leaks in real time. The

research project consists in using a large number of ultrasonic flow meters connected

wirelessly through an infrastructure based on like a wireless sensor network.

The assignment seeks to use these two technologies due to the fact of ultrasonic flow

meters being a non-invasive technique under employed in pipelines flow measurement. In

addition to this, ultrasonic flow meters installation tolerates the pipeline’s operation without

requiring major interventions.

Regarding the choice of wireless sensor network its deployment aims to cover an

application area that was been slightly covered yet.

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1.3 Work Plan

The thesis will be developed over a period of approximately four months. During this

period, the performed tasks are intended to meet the objectives defined above. The work

plan undertaken during the research project is presented in Error! Reference source not

found..

Figure 1.2 - Thesis work Plan

During the course of the dissertation thesis it will be possible to check in [5] a full

description of the work carried out in each week as well some further information related

with the project.

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Chapter 2

Flow Measurement

This chapter presents a literature review of the flow measurement techniques, giving

particular attention to use the flow meters. The chapter has been organized in four different

sections:

• The first section gives an overview of the flow measurement systems (FMS), its

importance and components.

• The subsequent section, highlights some basic principles involved in the process

of flow measurement.

• The working principle of some types of non-invasive electronic flow meters,

within the context this thesis is covered in section 2.3.

• Finally, the end of the chapter, discusses the correlation between flow

measurement techniques and leakage detection.

2.1 Background

As its name suggests, flow measurement is a technique used in fluids measurement for

both gases and liquids. The importance of quantifying this phenomenon is a consequence of

the need to transport the fluid from one point to another.

The application areas of flow measurement are wide and crucial. Either for charging some

supplied material or controlling industrial process, the task has to be performed accurately as

its value can affect many other process’ variables such as pressure or temperature. For

instance, in the operation and control of pipelines - LDS, flow measurement plays the most

important role [6, 7].

As stated previously, flow measurement is connected with the need to convey a fluid. This

transference occurs in a physical medium, which is frequently a pipe or pipeline. In order to

achieve the requirements of a flow measurement systems it is necessary to equip the physical

medium with sensors that have the ability to measure flow – flow meters. Other flow

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measurement systems require additional devices to measure relevant data, such as pressure

sensors, temperature gauges or other pertinent instrumentation devices.

In addition to this, it is necessary to provide the system with a signal conditioner

component that correlates the measured value with a physical value, and data acquisition

module to empower the control and monitoring of the system.

Despite not being mandatory, the incorporation of a communication module to gather

data and remotely control the process can be considered.

The composition of a flow measurement system (FMS) is illustrated in Figure 2.1

Figure 2.1 - Block diagram of a flow measurement system [7].

The architecture and technology employed in each flow measurement system (FMS) can be

different accordingly to the requirements. Some of these issues are going to be examined into

further detail in the next sections.

2.2 Basic Principles

Before discussing the topic of flow meters in detail it is necessary to start with the basics

of flow measurement theory. These concepts constitute the basis to understand the

instrumentation systems based on flow.

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2.2.1 Flow Definition

The volumetric flow rate in fluid dynamics, commonly known as flow rate, is the volume

of a fluid that passes through a given surface per unit time, i.e. the velocity of a certain fluid

times a certain surface. In equation 2.1 it is seen that given an area A at a designated point

and a fluid flowing through it with an average velocity V, the flow rate is [8]:

! = !   ∙  ! (2.1)

!"#$  !"#$ = !"#$%&'(  ×  !"#$ =  !!   ∙  !! = !3

!      (2.2)

2.2.2 Reynolds Number

The properties of a fluid, such as velocity, density or viscosity, affect the behaviour of the

fluid itself. Accordingly to these physical properties, the flow pattern of a fluid can be

classified in laminar or turbulent.

The flow state of a fluid is considered laminar or streamlined when the paths of the fluid

particles are parallel to each other and to the tube walls. As the fluid velocity increases it

reaches a critical value and the arrangement of the fluid particles becomes chaotic. At this

point the fluid particles are no longer parallel to the tube walls and a transverse velocity is

evident This form of flow pattern is called turbulent [9].

Figure 2.2 illustrates the arrangement of the particles in laminar and turbulent flows,

respectively.

Figure 2.2 - Laminar Flow versus Turbulent Flow [10]

In order to be feasible to study the flow of fluid along a channel, especially a closed one

like a pipeline, it is helpful to use a criterion that allows comparing results of observations

made under different conditions. Osborne Reynolds carried out a work on this subject and

formulated his data into a dimensionless number – Reynolds Number [9, 11].

!" = !  ∙  !  ∙  !! (2.3)

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Where:

Re is the Reynolds number;

D = the size of the channel (in circular channels like a pipe D is the diameter of the pipe);

! = velocity of the fluid;

ρ = density of the fluid;

µ = viscosity of the fluid;

Based on Reynolds number, fluids can be classified in laminar flow, for values lower than

2000, and turbulent flow, for Reynolds number above 4000. For values between 2000 and

4000 the flow is said to be in the transition region and classed as transition flow [8, 9, 11].

Another characteristic that can be inferred from Reynolds number is the distribution of the

velocity across the diameter of a pipe. This characteristic, designated by flow profile can be

different in agreement with the Reynolds number. For the laminar flow the profile is

parabolic. This means that the velocity at the center is greater than the mean velocity

(approximately twice the mean velocity). As for the turbulent flow, the profile is fairly [8].

The difference between these two flow profiles is evidenced in Figure 2.3.

Figure 2.3 - Flow profile of a fluid [12]

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2.2.3 Energy Of A Fluid

The understanding of the law of the conservation of energy and types of energy associated

with the flow of a fluid are essential for the understanding of the Bernoulli’s principle

(Section 2.2.4) that will be covered in the next subsection.

The types of energy associated with the movement of a fluid comprise [9]:

• Potential Energy – A fluid has potential energy as a result of its position with

respect to some fixed level.

• Kinetic Energy – The fluid will have kinetic energy as a consequence of its velocity.

This form of energy is also known as energy of motion.

• Pressure Energy – A fluid has pressure energy by virtue of its pressure.

• Internal Energy – A fluid has internal energy due to its temperature and chemical

makeup.

2.2.4 Bernoulli’s Principle

Bernoulli's Principle, published in 1738 by Daniel Bernoulli, takes a considerable

importance when we are talking about fluids flow. As “all fluid flow formulas in a closed

pipe are based on Bernoulli’s Theorem” [9], and as this thesis concerns the leakage detection

of a fluid in a pipeline, it is important to study this topic meticulously.

Bernoulli’s theorem states that for an inviscid fluid within a closed pipeline the sum of all

the fluids’ types of energy is constant at any point along the pipeline – principle of the

conservation of energy [13].

This physical phenomenon can best be described by an example presented in [9].

Figure 2.4 - Hydraulic condition for pipe flow [9]

Considering 1 kg of fluid entering the pipe at section 1. The fluid’s energy at each section

of the pipe is the result of the sum of each type of energy (Described in Energy Of Fluid).

Therefore, the energy at section 1 and 2 is:

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E! =  Potencial  Energy + Kinetic  Energy   + Pressure  Energy + Internal  Energy

= Z! ∙ g +!!V!! + p! ∙ v! + I! (2.4)

E! =  Potencial  Energy + Kinetic  Energy   + Pressure  Energy + Internal  Energy

= Z! ∙ g +!!V!! + p! ∙ v! + I! (2.5)

Recalling to the principle of conservation of energy, which states that energy cannot be

created nor destroyed, and since the energy cannot leave the pipe:

Energy at Section 1 (E!) = Energy at Section 2 (E!)

Z! ∙ g +!!V!! + p! ∙ v! + I! = Z! ∙ g +

!!V!! + p! ∙ v! + I! (2.6)

If the temperature of the fluid remains the same, the internal energy remains the same

(I! = I!) which means that equation 2.6 reduces to

Z! ∙ g +!!V!! + p! ∙ v! = Z! ∙ g +

!!V!! + p! ∙ v! (2.7)

Considering the particular case of liquid fluids. Since they are considered to be

incompressible, its density does not change significantly and therefore its volume will remain

constant and as consequence equation 2.7 can be rewritten as:

Z! +!!!

!"+ !!

!∙!= Z! +

!!!

!"+ !!

!∙! (2.8)

Back to Figure 2.4 it is possible to detect a differential height between the two sections.

This difference is given by:

ℎ = !! +!!!∙!

− !! +!!!∙!

(2.9)

Replacing in equation 2.8 presented above:

ℎ = !!!

!!− !!!

!! (2.10)

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Therefore, !!! − !!! = 2!ℎ (2.11)

Now the volume of liquid flowing along the channel per second will be given by Q m3

where ! = !! ∙ !! = !! ∙ !! (2.12)

!! =!!∙!!!!

(2.13)

Substituting in equation 2.11:

!!! 1− !!!

!!!= 2!ℎ (2.14)

and dividing by 1− !!!

!!! and taking the square root of both sides

!! =!!!

!!!!!

!!!

(2.15)

the factor !

!!!!!

!!!

is called velocity of approach factor and it is often represented by E.

Recalling to equation 2.12 the volume of liquid flowing in the pipe is:

! = !! ∙ !! = !! ∙ ! 2!ℎ (2.16)

Note that the equations presented above only apply to laminar flow and not to turbulent.

To determine the actual flow, it is necessary to take into account other parameters. Also

note, that the effects of viscosity have been ignored in the above equation. In order to

determine the actual flow an additional factor would have to be considered - Discharge

coefficient. To contemplate these and other factors should be consulted the BS 1043 Part 1

1964 [9].

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2.3 Flow Meters

After reviewing the basic principles involved in the process of flow measurement we can

proceed to the literature review on flow meters.

In this section will only convers the study of non-invasive electronic flow meters, as

previously highlighted. This section focuses on the analysis of three different kinds of flow

meters: electromagnetic, ultrasonic and cross-correlation. Further reference is also made

at the end of the section to other types of flow meters providing a brief summary of the

working principle, major application, advantages, disadvantages and variants of different

flow meters.

2.3.1 Electromagnetic Flow Meter

The working principle of this type of flow meters, also called magmeters, is based on

Faraday’s law of electromagnetic induction. According to Faraday’s law “if an electric

conductor moves in a magnetic field, an electromotive force (EMF) is induced whose

amplitude is dependent on the force of the magnetic field, the velocity of the movement,

and the length of the conductor.” See equation 2.17 [9]

! ∝ ! ∙ ! ∙ ! (2.17)

Where:

E is the electromotive force (EMF);

B = magnetic field density;

! = rate at which the conductor is cutting the magnetic field;

l = length of the conductor;

In this type of meter, the fluid flowing through the magnetic field is used as conductor

and therefore has to be a conductive fluid. Unfortunately, this excludes most petroleum-

based flows that are not conductive fluids [14].

To sum up, the working principle of electromagnetic flow meters, which is evidenced in

Figure 2.5, stated in [9] refers to BS 5792 1980 – The specifications for electromagnetic flow

meters.

“If the magnetic field is perpendicular to an electrically insulating tube through which a

conductive liquid is flowing, a maximum potential difference may be measured between two

electrodes positioned on the wall of the tube such that the diameter joining the electrodes

is orthogonal to the magnetic field.” [9]

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Figure 2.5 - Electromagnetic flow meter [14]

2.3.2 Ultrasonic Flow Meter

In the literature were identified two possible techniques for the use of ultrasonic flow

meters: Doppler and Transit-time. Below is presented these two different techniques for

flow measurement.

Doppler Flow Meter

The origin of the name of this technique comes from the working principle in which this

meter is based – Doppler effect. According to it, “the frequency of sound changes if its

source or reflector moves relative to the listener or monitor” [9]

The Doppler flow meter use a single ultrasonic transducer, which enclosures both a

transmitter and a receiver, installed on the monitoring pipe wall. The flow meter sends an

ultrasonic beam of frequency !! into the fluid at an angle ! as it is illustrated in Figure 2.6.

The ultrasonic pulses send by the transmitter will reflect on some of the entrained particles

or bubbles of the fluid back to the ultrasonic receiver with a frequency !! (See Figure 2.6) [9,

14].

The equations correlated to the fluid movement are shown below [9]:

!! = !! ± 2! ∙ !"#$ ∙!1! (2.18)

The equation 2.18 can be rewritten as:

! = !(!2−!1)2∙!1∙!"#$

(2.19)

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Where:

! is the velocity of the fluid;

!! = frequency of the ultrasonic beam sent – transmitter;

!! = frequency of the ultrasonic beam reflected – receiver;

! = angle of attack between the transducer and the fluid;

C = velocity of the sound in the fluid;

Figure 2.6 - Ultrasonic flow meter - Doppler [9]

Transit-Time Flow Meter

The difference between this ultrasonic technique and the one described previously

(Doppler) is that this technique is based on the transmission of an ultrasonic beam through

the flow stream. Contrarily to Doppler technique, this method does not depend neither on

fluid’s discontinuities nor entrained particles [9].

The operation principle of this method is based on the transmission of ultrasound signals

between two transducers separated by the fluid. In order to measure the fluid velocity, the

transducers placed in the pipe wall “transmit ultrasonic pulses with the flow and against the

flow to a corresponding receiver”. This means that each ultrasonic sensor works as both

transmitter and receiver like is evinced in Figure 2.7 [14].

Figure 2.7 - Ultrasonic flow meter - Transit-time [9]

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The equations given below concern the operating principle of transit-time flow meter

taken from the example in [14] (See Figure 2.8)

Downstream equation

t!" = L(C+v∙cosθ) (2.20)

Upstream equation

t!" = L(C-­‐v∙cosθ)

(2.21)

Solving equation 2.20 and 2.21 results in equations 2.22 and 2.23:

v = L2∙cosθ ∙

tdu-­‐tudtdu∙tud

(2.22)

C = L2 ∙

tdu+tudtdu∙tud

(2.23)

Where:

v is the mean velocity of the fluid;

C is the velocity of the sound in the fluid;

t!" = transit time between transducer u to d;

t!" = transit time between transducer d to u;

L = length between transducers;

θ = angle of attack between the transducer and the fluid;

Figure 2.8 - Working principle of transit-time flow meter [14]

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2.3.3 Cross-Correlation Flow Meter

Almost every fluid flowing in a pipe or tube presents random variations that can occur for

instance in fluid’s density or temperature. Appropriate sensors installed on some specific

locations can detect these variations. By placing transducers separately by a distance L, as is

shown in Figure 2.9, the upstream transducer will notice the variation (e.g. pressure or

temperature) t seconds before the downstream transducer. The flow velocity is calculated

dividing the distance L (distance between transducers) by transit time t. “In practice the

random fluctuations will not be stable and are compared in a cross-correlator which has a

peak response at transit time T, and correlation velocity V = L/T, meters per second.” [9]

! = !! (2.24)

Where:

! is the flow velocity;

L = distance between transducer 1 and transducer 2;

t = time difference between fluctuation detection in transducer 1 and transducer 2;

Despite being possible in principle to measure almost every fluid, a narrow range of flow

measurement systems use this type of flow meter due to the slow response time of those

systems [9].

Figure 2.9 – Cross-correlation flow meter [9]

2.3.4 Comparison Of Flow Meters

The table provided below (Table 2.1) was taken from [15] and summarizes the main

characteristics of the various flow meters technologies reviewed above.

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Table 2.1 - Comparison of flow meters technologies. Taken from [15].

Flow meter

Technology

Accuracy

(+/-) Turndown Fluids

Pipe Sizes

(in)

Maximum

Pressure

(psig)

Temperature

range

(ºF)

Pipe

run

Electromagnetic 0.2 to 2% R 10:1 L 0.15 to 60 5000 -40 to 350 Short

Ultrasonic

Doppler 1 to 30% R 50:1 L, G, SL 0.5 to 200 6000 -40 to 250 Long

Ultrasonic

Transit Time 0.5 to 5% R Down to zero

flow L, G 1 to 540 6000 -40 to 650 Long

Correlation 0.5% R 10:1 L, G, SL 1 to 60 Piping limits

To 600 Long

Where:

R= Rate

G= Gas

L= Liquid

SL= Slurry

Table 2.2 presents a brief summary of the working principle, major application,

advantages, disadvantages and variants of different types of flow meters

Table 2.2 - Types of flow meters and its characteristics. Taken from [7].

Flow Meter

Type

Primary

Working

Principle

Quantity

Measured Advantages Disadvantages Meter Name

Differential

Pressure

Pressure drop caused by pipe’s restriction

Volume (versatile – almost all gases and low viscosity liquids)

Low-cost, versatile, robustness, variety of versions,

Square root dependence, affected by pressure and density changes, high pressure drop (exception for nozzles)

Orifice, nozzle Venture, elbow, v-cone, Pitot tube, Annubar

Turbine Rotating device

Volume (lubricating fluids)

No supply power requirements, extreme temperatures and pressures, certified for gases

Only for low viscosity, moving parts, sensitive to contamination and vibration

Single rotor, dual rotor, paddle wheel, propeller, tangential

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Flow Meter

Type

Primary

Working

Principle

Quantity

Measured Advantages Disadvantages Meter Name

Variable Area

Dynamic balance (impulsion, weight and dragging)

Volume (liquid and gas applications with enough density)

Low-cost, no supply power requirements, simplicity, versatile

Vertical installation, constant pressure loss (inaccuracy low fluid’s flow), affected by density and temperature changes

Rotameters- different variants of float designs and sensing systems

Magnetic Electromagnetic induction

Volume (almost all measurements as long as the conductivity is above a minimal value)

No moving parts, non invasive, no pressure loss, no dependence of flow regime, not affected by temperature, density, conductivity and concentration changes

Only liquids applications, lower conductivity limit (0.05 µS/cm)

Magnetic DC- no electrodes two-wire partially full

Oscillatory Coandă effect

Volume (application to a large variety of liquids as long as RN is above a minimal value)

No moving parts, robustness, suitable for different fluid types (gas, liquid, steam), linear relation between measurement and fluid flow

Fluids that exceed a minimum velocity RN restriction, fluids with viscosity above a minimal value, complex signal’s conditioning

Fluidic vortex

Target

Force of the fluid in a fixed body (target)

Volume (clean fluids, minimum movement quantity)

Low-cost, good performance in large pipes

Restrictions on RN, fluid’s velocity, material of construction, low accuracy, almost impossible calibration

Target

Positive

Displacement

Measurement of fixed fluid’s volume per rotation

Volume (clean and non-abrasive liquids)

High accuracy, no supply power requirements, bidirectional operation, no RN restrictions

Only for liquids, high pressure drop, moving parts, sensitivity to contamination and overloading

Helical gear, nutating disc, oscillating piston, oval gear, rotary

Ultrasonic

Acoustic waves or vibrations

Volume (clean liquids and some gases, but problematic for the last)

No moving parts, it could be non-invasive (transducers are outside the pipe), no pressure drop, linear relation between measurement and fluid’s flow, on line calibration

Good accuracy only for liquids, error due to deposits, errors caused by gas bubbles, affected by sound, velocity, temperature, concentration and density changes

Doppler transit time pulse repetition

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Flow Meter

Type

Primary

Working

Principle

Quantity

Measured Advantages Disadvantages Meter Name

Insertion

Measurement of fluid’s velocity in critical positions (e.g.: pipe’s axis)

Volume (liquids, gas and steam in large pipes)

Depends on transducer types because it can be implemented using almost all flow meter’s working principles

Only large pipes, requirement of data processing for acceptable values of accuracy, RN restriction (turbulent flow regime), large pressure drop

One for each type of transducer (metering principle)

Correlation

Correlation of measurement data captured in different positions

Volume (depend on flow meter type use for correlation purposes)

Typically non-invasive measurement method

(depend on flow meter type use for correlation purposes)

One for each type of transducer (metering principle)

Open Chanel

Sheet of fluid above a crested dam or variable height in a restriction (Parshall)

Volume (liquid flow measurements usually in irrigation, drains and water works systems)

Unique solution for measurements in open channels (e.g.: irrigation systems, river flows)

Pressure loss, not versatile

Weirs Parshall flume

Coriollis

Conservation of angular momentum

Mass (measurement of: liquids, gases with restrictions, harsh chemicals, density)

True mass measurement, no RN restrictions, high accuracy, unaffected by pressure, temperature and density

Acceptable accuracy only for liquids, vibration sensitivity, large size limitations

Coriollis Hydraulic Wheatstone bridge

Thermal

Thermal properties of materials

Mass (measurement of gases)

True mass measurement, robustness for industrial and vehicle applications, large flow range

Only for gases, non-linear inference measurement of mass, non-linear output signal, bubbles sensitivity

Hot Wire Anemometer

2.4 Detection Of Leaks

Till now we have seen some issues about flow measurement. These include both the basic

concepts involved in the measuring task and the instrumentation equipment to its

quantification. However, the most important topic to address within the context of this thesis

is: How can a leak be detected by measuring the flow of a fluid in a pipeline?

The idea behind the detection of leaks has already been addressed. The detection of leaks

is based on the conservation of mass that states that “, the amount of fluid moving through a

meter is neither added to nor taken from as it progresses from point 1 to point 2.” [8].

30

Therefore, if two consequent flow meters, one placed at point 1 and other placed at point 2,

diverge in the measured value would mean that there is a leak somewhere between these

two points.

The consequent product loss can be calculated by the difference between instantaneous

inlet and outlet flows and the average of the integrated inlet and outlet flows as it shown in

[6] and described by equation 2.25 [6].

∆! = !!" − !!"# − !! (2.25)

Where:

∆! is the leakage volume;

!!" = Metered inlet flow;

!!"# = Metered outlet flow;

!! = Calculated as the average of the integrated inlet and outlet flows;

This last term (!!) is calculated as the average of the integrated inlet and outlet flow. In a

pipeline without leakage this term is zero as the integrated inlet and outlet have symmetrical

values.

To sum up, either for identifying a leak or determining its location, a cooperation of

different flow meters installed along the pipeline is required. It is within this context that

WSNs emerge. In the next chapter this topic will be discussed in detail.

Summary

The more important issues of flow measurement and leak detection systems were

reviewed in this chapter. The relevant information about the basic principles, formulas, and

theory involving the movement of fluids were analyzed in detail.

A great emphasis to flow meters and its measurement techniques was also given. Three

types of flow meters were discussed in the context of this thesis: electromagnetic, ultrasonic

(Doppler and Transit-time) and cross-correlation.

Finally at the end of the chapter, the correlation between flow measurement and leakage

detection was addressed.

31

Chapter 3

Sensor Networks

This chapter introduces the sensor networks’ state of the art. The chapter covers the

following topics:

• Background on wireless sensor network.

• Application areas for sensor networks;

• Challenges and requirements;

• Energy scavenging;

3.1 Background

A sensor network is a cluster of nodes that are connected using a communication

infrastructure for either monitoring or control purposes. The communication infrastructure of

a sensor network can be either wired or wireless. The present chapter gives a particular

emphasis to the study of wireless sensor networks (WSNs). However, most of the topics cover

can also be applied to wired sensor networks [16, 17]

Wireless sensor networks (WSNs), consists of a wireless network composed by large

number of sensor devices. These devices, called nodes, cooperate with each other to perform

a sensing task in a specific physical environment. Each sensor node is equipped with a [18]:

• Transducer which generates electrical in accordance with the measured value;

• Microcontroller which processes data. Is responsible for acting or sensing over

the environment;

• Memory which store programs and intermediate data;

• Transceiver which receives and transmits data over the communication

infrastructure i.e. antenna;

• Power Source which supplies electrical power for node’s operating;

32

Figure 3.1 shows the typical architecture of a sensor network and sensor node.

Figure 3.1- Typical architecture of sensor network and sensor node. Based on [18]

3.2 Application Areas For WSN

In the latest years the interest in WSNs has increased significantly due to both research

and industrial players. This growing interest took this technology to be considered by

Technology Review at MIT as one of the “10 emerging technologies that will change the

world” [19].

The application areas for WSNs are immense. From military usage to environmental

monitoring, there are an unlimited number of possibilities for new application purposes for

WSNs. This section addresses some of the most relevant examples.

3.2.1. Military Application

The usage of WSNs for military purposes can be a crucial part for military command

control, communication, computing, intelligence, surveillance, reconnaissance and targeting

(C4ISRT) systems. Some of the military application for WSNs includes: monitoring friendly

troops, Targeting and monitoring enemy forces or detecting biological and chemical attacks.

We will look in further detail which one of these applications [20, 21]

Monitoring Friendly Troops

Determining the best course of action in a battlefield is a very complex task that requires

knowing the position and status of every personnel, equipment and vehicle. This kind of

application aims to ease the coordination and monitoring among the friendly troops by using

WSNs.

33

Every troop, vehicle, equipment and critical ammunition has to be equipped with attached

sensors that monitors and reports the status to a sink node (basestation node illustrated in

Figure 3.2). The information gathered in the basestation is sent to the troops leaders or

command centers to determine the best course of action in accordance with that information

[20, 21].

An example of monitoring friendly troop application is illustrated in Figure 3.2.

Figure 3.2 - A sensor network for military surveillance application. From [22].

Targeting And Monitoring Enemy Forces

The purpose of this application is collecting valuable information of the enemy forces. The

sensor nodes, which are installed in the battlefield area, can detect a presence of an enemy

and disseminate this information throughout the network. This information not only would

help to determine the position of the enemy as also would empower the friendly troops to

strategically position in the battlefield and determine the best course of action, which

minimizes any possible casualties [20, 21].

An example of targeting and monitoring enemy forces is exhibited in Figure 3.3.

34

Figure 3.3 - Enemy target localization and monitoring using WSNs. From [20].

Detecting Biological And Chemical Attacks

In a situation of a biological or chemical attack it is essential to be close the ground zero

for timely and accurately detect the agents involved.

This application consists in deploying spatially distributed sensor nodes in the friendly

regions to detect the presence of toxic substances on the environment. This way, sensor

networks can provide an early warning in a situation of a biological or chemical attack [21].

3.2.2. Environmental Monitoring

Environment monitoring is a natural candidate for the development of sensor networks

applications due to the characteristic of variables to monitor, which are usually spatially

distributed over large areas (e.g. temperature or pressure) [23].

Several applications can be considered in this context: Forest fire detection, animal

tracking and habitat monitoring or monitoring the environmental conditions [21].

Forest Fire Detection

As seen in the military application case, WSNs can densely cover a wide area. This type of

application uses sensor nodes to detect the exact location of a fire before it starts to spread

uncontrollably. As soon as a node detect a fire it disseminates a message over the network

till arrives the sink node. Afterwards a message would be sent to fire fighters with the exact

location of the fire [19-21].

Figure 3.4 illustrates the scenario of a fire detection using WSNs.

35

Figure 3.4 - Forest-fire monitoring application. From [20].

Animal Tracking And Habitat Monitoring

This kind of application permits researches to gather important data about a specifically

animal or habitat in an unobtrusive manner.

A well-succeeded example of animal tracking and habitat monitoring is identified in the

literature [19, 20].This example is one of the world's most advanced experiments in wireless

networking as it covers an area of approximately 90 hectares on Great Duck Island (USA). The

application focuses in the habitat monitoring of Leach’s Storm Petrel, a common seabird in

the western North Atlantic. Humans cannot perform the activity monitoring of this particular

specie as it can lead to nest abandonment or increased predation on chicks or eggs. For this

reason, the usage of WSNs is the only form to obtain information.

Monitoring The Environmental Conditions

WSNs also can be used for the measurement of environmental data. This comprises

temperature, pressure, humidity, solar radiation, chemical pollutants and wind speed among

others.

Some examples of this type of application comprehend the measurement of chemical

pollutants in garbage dump sites; surveillance the marine ground floor an understanding its

erosion process for the construction of offshore wind farms [18].

36

3.2.3. Health Applications

Health is one of the application areas covered by WSNs. Some relevant applications in this

area are: drug administration, monitoring patient’s physiological data, tracking doctors and

patients, diagnosis or help the disable [21]. Monitoring physiological data and drug

administration is covered below.

Monitoring Physiological Data And Drug Administration

Patients can be attached with sensor nodes that would not only monitor the patient’s

physiological data but also include information about patient’s medical record, such as

allergies, prescribed medications, chronic diseases, among others.

This would help both doctors and medical personnel during the patients’ treatment as this

would permit: storing patients’ information for long periods of time and submit to doctors’

analysis, minimizing the adverse of drugs or preventing from erroneous drug prescription [21].

An example of a potential health monitoring application is shown in [24] for glucose-level

monitoring. Diabetes is a disease that requires constant observation of blood sugar level.

Using WSN for this purpose would not only guarantee a continuous sugar level monitoring but

also alert the individual to take corrective measures.

3.3 Challenges & Requirements For WSNs

Literature [17, 18, 20, 21, 25-28] identifies several challenges and requirements that are

shared among almost every WSN application. These comprehend both software and hardware

challenges to engineers. In this section we will look into further detail of some of the most

critical properties of a WSN system.

3.3.1. Fault Tolerance

The fault tolerance of a system is the property of a system to continue to operate properly

in a situation of failure. This property is crucial in a WSN as nodes may run out of energy,

might be damaged or the communication with a certain node can be interrupted for a long

periods of time. The recognition and exhibition of these situations is desirable.

To support this property is usually required some kind of redundancy in the deployment,

which involves more nodes than the necessary.

3.3.2. Security

WSNs are designed to operate in hostile environments (e.g. battlefield, f), sensor nodes

should support security at all levels of the network. The following security characteristics

must be guaranteed [21]:

• Access control in order to prevent unauthorized access to sensor nodes;

37

• Message integrity to guarantee non-unauthorized changes to the message;

• Confidentiality, which consists in encrypting exchanged messages between nodes

and assures that only the nodes with the secret key can communicate;

• Replay Protection that involves preventing a sensor node from gaining network

access by reusing an authentic packet;

3.3.3. Scalability

WSNs are usually composed by large number of nodes that might be spatially distributed.

Therefore, the employment of the WSN’s architecture and protocols must be able to scale

the network’s nodes.

3.3.4. Energy Efficiency

The biggest problem in WSNs applications is energy. Sensor nodes are usually powered on

batteries that have a limited amount of energy. Managing the energy source is therefore

mandatory. In addition to this, energy-efficient is the key to a long lasting life of the

application, as when a sensor node runs out of energy it can no longer fulfill its role.

In order to increase application’s lifetime, energy scavenging can be considered. Next

section covers some of the options that can be considered in energy scavenging.

3.4. Energy Scavenging

An important issue to embrace within the context of WSNs application is energy

scavenging, as applications may require uninterrupted operation for long periods of time and

in inhospitable environments. Energy scavenging is the term used for meaning energy search

and collect from the environment. The review of this procedure, also referred as energy

harvesting, is important in application where replacing batteries or supplying with wired

energy is unfeasible. Note that, using energy scavenging to recharge battery does not exclude

the problem of nodes running out of energy. This technique just extends battery lifetime.

The scavenging sources analyzed in this section are the main sources of ambient energy

considered suitable for use with WSNs by the authors from [29].

3.4.1. Solar

Solar power is the one of the most common forms of energy harvesting. Although,

photovoltaic panels require incident light to generate electricity and a low-power maximum

power point tracker (MPPT) to ensure that energy is not lost from the scavenging source to

the sensor node batteries [29].

Despite these disadvantages, solar power is still being a high viability for energy

harvesting.

38

38

3.4.2. Mechanical

Man has been using this kind of energy for centuries. Take the example of a mill or

watermill where wind is used to transform corn into flour.

Vibrational, kinetic and mechanical energy can be used for harvesting energy from

movement objects. Vibration energy for instance can be harvested from the environment by

using piezoelectric capacitors. This kind of energy is highly potential in bridges or railways

were vibration is present all around [29].

3.4.3. Thermal

Temperature variation can also provide a means by which energy can be scavenged from

the environment. A temperature difference between two junctions of a conducting material

generates electrical current. Thermal energy harvesting consists in generating electricity by

using this principle [29].

There are some commercial products, like citizen wristwatches, that use this technology

to recharge batteries [20]. In that application temperature difference between human body

and the surrounding environment is used to generate energy.

3.4.4. Comparison Of Scavenging Sources

Table 3.1 summarizes the main characteristics of various potential scavenging sources

analyzed in this section.

Table 3.1 - Comparison of various potential power sources for WSNs. Taken from [20].

Power Source P/cm3

(µW/cm3) Secondary

Storage Needed

Voltage

Regulation

Commercial

Available

Solar (outside) 15000a Usually Maybe Yes

Solar (inside) 10a Usually Maybe Yes

Temperature 40a,b Usually Maybe Limited

Air Flow 350c Yes Yes No

Vibrations 200 Yes Yes Limited

a Denotes sources whose fundamental metric is power per square centimenter per cubic centimeter

b Demonstrated from a 5ºC temperature differential. c Based on reported values at an air velocity of 5m/s and 11% conversion efficiency.

39

Summary

An effort has been made to give an overview of WSNs in this chapter. The concepts of

WSN, sensor node and node composition were reviewed.

A great part of the chapter was spent in analyzing the various areas of application for

WSN, its architectures and usage advantages. It has also been covered the main challenges

and requirements identified in the literature and shared among WSNs applications.

Finally at the end of the chapter, scavenging energy sources have been addressed. Three

types of energy sources were discussed within the context of WSNs usage.

41

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