The notion that agriculturally productive land may be treated as a relatively homogeneous resource at thewithin-field scale is not sound. This assumption and the subsequent uniform application of planting material,chemicals and/or tillage effort may result in zones within a field being under- or over-treated. Arising fromthese are problems associated with the inefficient use of input resources, economically significant yield losses,excessive energy costs, gaseous or percolatory release of chemicals into the environment, unacceptable long-term retention of chemicals and a less-than-optimal growing environment. The environmental impact of cropproduction systems is substantial. In this millennium, three important issues for scientists and agrariancommunities to address are the need to efficiently manage agricultural land for sustainable production, themaintenance of soil and water resources and the environmental quality of agricultural land.Precision agriculture (PA) aims to identify soil and crop attribute variability, and manage it in an accurate andtimely manner for near-optimal crop production. Unlike conventional agricultural management where anaveraged whole-field analytical result is employed for decision-making, management in PA is based on site-specific soil and crop information. That is, resource application and agronomic practices are matched withvariation in soil attributes and crop requirements across a field or management unit. Conceptually PA makeseconomic and environmental sense, optimising gross margins and minimising the environmental impact ofcrop production systems. Although the economic justification for PA can be readily calculated, concepts suchas environmental containment and the safety of agrochemicals in soil are more difficult to estimate. However,it may be argued that if PA lessens the overall agrochemical load in agricultural and non-agriculturalenvironments, then its value as a management system for agriculture increases substantially.Management using PA requires detailed information of the spatial and temporal variation in crop yieldcomponents, weeds, soil-borne pests and attributes of physical, chemical and biological soil fertility. However,detailed descriptions of fine scale variation in soil properties have always been difficult and costly to perform.Sensing and scanning technologies need to be developed to more efficiently and economically obtain accurateinformation on the extent and variability of soil attributes that affect crop growth and yield. The primary aimof this work is to conduct research towards the development of an �on-the-go� proximal soil pH and limerequirement sensing system for real-time continuous management of acid soil. It is divided into four sections.Section one consists of two chapters; the first describes global and historical events that converged into thedevelopment of precision agriculture, while chapter two provides reviews of statistical and geostatisticaltechniques that are used for the quantification of soil spatial variability and of topics that are integral to theconcept of precision agriculture. The review then focuses on technologies that are used for the completeenumeration of soil, namely remote and proximal sensing.Section two comprises three chapters that deal with sampling and mapping methods. Chapter three provides ageneral description of the environment in the experimental field. It provides descriptions of the field site,topography, soil condition at the time of sampling, and the spatial variability of surface soil chemicalproperties. It also described the methods of sampling and laboratory analyses. Chapter four discusses some ofthe implications of soil sampling on analytical results and presents a review that quantifies the accuracy,precision and cost of current laboratory techniques. The chapter also presents analytical results that show theloss of information in kriged maps of lime requirement resulting from decreases in sample size. The messageof chapter four is that the evolution of precision agriculture calls for the development of �on-the-go� proximalsoil sensing systems to characterise soil spatial variability rapidly, economically, accurately and in a timelymanner. Chapter five suggests that for sparsely sampled data the choice of spatial modelling and mappingtechniques is important for reliable results and accurate representations of field soil variability. It assesses anumber of geostatistical methodologies that may be used to model and map non-stationary soil data, in thisinstance soil pH and organic carbon. Intrinsic random functions of order k produced the most accurate andparsimonious predictions of all of the methods tested.Section three consists of two chapters whose theme pertains to sustainable and efficient management of acidagricultural soil. Chapter six discusses soil acidity, its causes, consequences and current management practices.It also reports the global extent of soil acidity and that which occurs in Australia. The chapter closes byproposing a real-time continuous management system for the management of acid soil. Chapter seven reportsresults from experiments conducted towards the development of an �on-the-go� proximal soil pH and limerequirement sensing system that may be used for the real-time continuous management of acid soil.Assessment of four potentiometric sensors showed that the pH Ion Sensitive Field Effect Transistor (ISFET)was most suitable for inclusion in the proposed sensing system. It is accurate and precise, drift and hysteresisare low, and most importantly it�s response time is small. A design for the analytical system was presentedbased on flow injection analysis (FIA) and sequential injection analysis (SIA) concepts. Two different modesof operation were described. Kinetic experiments were conducted to characterise soil:0.01M CaCl2 pH(pHCaCl2) and soil:lime requirement buffer (pHbuffer) reactions. Modelling of the pHbuffer reactions describedtheir sequential, biphasic nature. A statistical methodology was devised to predict pHbuffer measurements usingonly initial reaction measurements at 0.5s, 1s, 2s and 3s measurements. The accuracy of the technique was 0.1pHbuffer units and the bias was low. Finally, the chapter describes a framework for the development of aprototype soil pH and lime requirement sensing system and the creative design of the system.The final section relates to the management of acid soil by liming. Chapter eight describes the development ofempirical deterministic models for rapid predictions of lime requirement. The response surface models arebased on soil:lime incubations, pHbuffer measurements and the selection of target pH values. These models aremore accurate and more practical than more conventional techniques, and may be more suitably incorporatedinto the spatial decision-support system of the proposed real-time continuous system for the management ofacid soil. Chapter nine presents a glasshouse liming experiment that was used to authenticate the limerequirement model derived in the previous chapter. It also presents soil property interactions and soil-plantrelationships in acid and ameliorated soil, to compare the effects of no lime applications, single-rate andvariable-rate liming. Chapter X presents a methodology for modelling crop yields in the presence ofuncertainty. The local uncertainty about soil properties and the uncertainty about model parameters wereaccounted for by using indicator kriging and Latin Hypercube Sampling for the propagation of uncertaintiesthrough two regression functions; a yield response function and one that equates resultant pH after theapplication of lime. Under the assumptions and constraints of the analysis, single-rate liming was found to bethe best management option.

The notion that agriculturally productive land may be treated as a relatively homogeneous resource at thewithin-field scale is not sound. This assumption and the subsequent uniform application of planting material,chemicals and/or tillage effort may result in zones within a field being under- or over-treated. Arising fromthese are problems associated with the inefficient use of input resources, economically significant yield losses,excessive energy costs, gaseous or percolatory release of chemicals into the environment, unacceptable long-term retention of chemicals and a less-than-optimal growing environment. The environmental impact of cropproduction systems is substantial. In this millennium, three important issues for scientists and agrariancommunities to address are the need to efficiently manage agricultural land for sustainable production, themaintenance of soil and water resources and the environmental quality of agricultural land.Precision agriculture (PA) aims to identify soil and crop attribute variability, and manage it in an accurate andtimely manner for near-optimal crop production. Unlike conventional agricultural management where anaveraged whole-field analytical result is employed for decision-making, management in PA is based on site-specific soil and crop information. That is, resource application and agronomic practices are matched withvariation in soil attributes and crop requirements across a field or management unit. Conceptually PA makeseconomic and environmental sense, optimising gross margins and minimising the environmental impact ofcrop production systems. Although the economic justification for PA can be readily calculated, concepts suchas environmental containment and the safety of agrochemicals in soil are more difficult to estimate. However,it may be argued that if PA lessens the overall agrochemical load in agricultural and non-agriculturalenvironments, then its value as a management system for agriculture increases substantially.Management using PA requires detailed information of the spatial and temporal variation in crop yieldcomponents, weeds, soil-borne pests and attributes of physical, chemical and biological soil fertility. However,detailed descriptions of fine scale variation in soil properties have always been difficult and costly to perform.Sensing and scanning technologies need to be developed to more efficiently and economically obtain accurateinformation on the extent and variability of soil attributes that affect crop growth and yield. The primary aimof this work is to conduct research towards the development of an �on-the-go� proximal soil pH and limerequirement sensing system for real-time continuous management of acid soil. It is divided into four sections.Section one consists of two chapters; the first describes global and historical events that converged into thedevelopment of precision agriculture, while chapter two provides reviews of statistical and geostatisticaltechniques that are used for the quantification of soil spatial variability and of topics that are integral to theconcept of precision agriculture. The review then focuses on technologies that are used for the completeenumeration of soil, namely remote and proximal sensing.Section two comprises three chapters that deal with sampling and mapping methods. Chapter three provides ageneral description of the environment in the experimental field. It provides descriptions of the field site,topography, soil condition at the time of sampling, and the spatial variability of surface soil chemicalproperties. It also described the methods of sampling and laboratory analyses. Chapter four discusses some ofthe implications of soil sampling on analytical results and presents a review that quantifies the accuracy,precision and cost of current laboratory techniques. The chapter also presents analytical results that show theloss of information in kriged maps of lime requirement resulting from decreases in sample size. The messageof chapter four is that the evolution of precision agriculture calls for the development of �on-the-go� proximalsoil sensing systems to characterise soil spatial variability rapidly, economically, accurately and in a timelymanner. Chapter five suggests that for sparsely sampled data the choice of spatial modelling and mappingtechniques is important for reliable results and accurate representations of field soil variability. It assesses anumber of geostatistical methodologies that may be used to model and map non-stationary soil data, in thisinstance soil pH and organic carbon. Intrinsic random functions of order k produced the most accurate andparsimonious predictions of all of the methods tested.Section three consists of two chapters whose theme pertains to sustainable and efficient management of acidagricultural soil. Chapter six discusses soil acidity, its causes, consequences and current management practices.It also reports the global extent of soil acidity and that which occurs in Australia. The chapter closes byproposing a real-time continuous management system for the management of acid soil. Chapter seven reportsresults from experiments conducted towards the development of an �on-the-go� proximal soil pH and limerequirement sensing system that may be used for the real-time continuous management of acid soil.Assessment of four potentiometric sensors showed that the pH Ion Sensitive Field Effect Transistor (ISFET)was most suitable for inclusion in the proposed sensing system. It is accurate and precise, drift and hysteresisare low, and most importantly it�s response time is small. A design for the analytical system was presentedbased on flow injection analysis (FIA) and sequential injection analysis (SIA) concepts. Two different modesof operation were described. Kinetic experiments were conducted to characterise soil:0.01M CaCl2 pH(pHCaCl2) and soil:lime requirement buffer (pHbuffer) reactions. Modelling of the pHbuffer reactions describedtheir sequential, biphasic nature. A statistical methodology was devised to predict pHbuffer measurements usingonly initial reaction measurements at 0.5s, 1s, 2s and 3s measurements. The accuracy of the technique was 0.1pHbuffer units and the bias was low. Finally, the chapter describes a framework for the development of aprototype soil pH and lime requirement sensing system and the creative design of the system.The final section relates to the management of acid soil by liming. Chapter eight describes the development ofempirical deterministic models for rapid predictions of lime requirement. The response surface models arebased on soil:lime incubations, pHbuffer measurements and the selection of target pH values. These models aremore accurate and more practical than more conventional techniques, and may be more suitably incorporatedinto the spatial decision-support system of the proposed real-time continuous system for the management ofacid soil. Chapter nine presents a glasshouse liming experiment that was used to authenticate the limerequirement model derived in the previous chapter. It also presents soil property interactions and soil-plantrelationships in acid and ameliorated soil, to compare the effects of no lime applications, single-rate andvariable-rate liming. Chapter X presents a methodology for modelling crop yields in the presence ofuncertainty. The local uncertainty about soil properties and the uncertainty about model parameters wereaccounted for by using indicator kriging and Latin Hypercube Sampling for the propagation of uncertaintiesthrough two regression functions; a yield response function and one that equates resultant pH after theapplication of lime. Under the assumptions and constraints of the analysis, single-rate liming was found to bethe best management option.

This thesis reports the design and fabrication of a low-cost reliable microelectrode array sensing platform and its application toward water quality monitoring, including heavy metal ion detection. Individually addressable microelectrodes were designed in a planar array on a nonconductive glass substrate by a photolithography method. The size, shape, composition, and functionality of the microelectrodes were theoretically explored in order to maximize performance. The microelectrode array sensing platform was proven and characterized in the K3Fe(CN)6 electrochemical standard using cyclic voltammetry. The sensor platform exhibited well defined voltammograms and had increased sensitivity relative to a commercially available microelectrode of similar size. Feasibility for application to heavy metal ions, copper and lead, detection in aqueous solutions was demonstrated utilizing the electrochemical method of anodic stripping voltammetry. Well defined voltammograms for the copper and lead ions were obtained with individual microelectrodes of the sensor platform, and compared against the similar sized commercially available microelectrode; increased sensitivity was observed.

To circumvent some inherent problems in the conventional ECG, this research reinvestigates an ‘unassisted’ approach which enables ECG measurement without the placement of leads on the body. Employed in this research is a widely accepted assumption that the electrical activity of the heart may be represented, largely, by a 3-D time-varying current dipole (3D-CD). From the PhysioBank database, mECG and fECG data were obtained, and Singular Value Decomposition (SVD) was performed to estimate the time-varying Vector ECG dipole. To determine the sensing matrix responsible for transforming the activity of the 3D-CD into the potential distribution on the surface of the medium, the ECG vector dipole signals are used to excite a 3D-CD in water medium of a specific shape-containing-ellipsoid model(s) in COMSOL tool. The sensing matrix thereby estimated is then utilized to reconstruct the 3D-CD signals from the signals measured by the probes on the surface of the medium. Fairly low NRMSEs (Normalized Root-Mean-Squared Errors) are attained. The approach is also successfully extended to the case of two ellipsoids, one inside the other, representing a pregnant female subject. Low NRMSEs (Normalized Root-Mean-Squared Errors) are again observed.

No description available.

Embora muitas cidades brasileiras estejam gradualmente implementando infraestruturas cicloviárias, a exposição dos ciclistas ao ruído ainda não é vista como um elemento a ser considerado no processo de planejamento. A partir deste pressuposto, o objetivo deste estudo é avaliar a exposição dos ciclistas ao ruído em São Carlos, SP, cidade média brasileira na qual cerca de 244 mil habitantes, 107 mil carros e 25 mil motocicletas foram contados em 2016. O estudo envolveu os seguintes procedimentos: i) definições preliminares e ajustes relativos às campanhas de coleta de dados, ii) coleta de dados, iii) validação de dados, iv) cálculo de níveis de exposição ao ruído e v) avaliação da exposição dos ciclistas ao ruído. Foram analisadas duas rotas. A primeira apresentava infraestrutura cicloviária (ciclovias ou ciclofaixas), em alguns dos 12 setores considerados para análise. A segunda rota foi dividida em dois setores, ambos sem infraestrutura cicloviária, mas com um excelente potencial para atrair viagens de bicicleta devido à localização privilegiada da área na cidade. A exposição ao ruído foi classificada de acordo com a percentagem média de valores de SEL (Sound Exposure Level) acima de 85 dBA e de acordo com valores de Lnp (Nível de Poluição Sonora). De maneira geral, os níveis de exposição dos ciclistas ao ruído foram classificados como \"muito alto\" ou \"alto\" em todas as 14 subdivisões das duas rotas, três das quais foram classificados como insalubres. Além disso, mesmo as seções com os menores valores de Lnp apresentaram quase metade das viagens para coleta de dados classificadas como \"muito altas\". É importante destacar que os locais, das partes mais ruidosas das duas rotas, tinham características distintas. Os trechos mais ruidosos da primeira rota foram registrados em uma ciclovia localizada ao longo de uma avenida larga, que margeia um rio e é cercada por áreas verdes, mas onde o limite de velocidade para carros é de 60 km/h. Há claramente um conflito aqui, dado que, apesar das condições de circulação seguras proporcionadas pela ciclovia e o agradável ambiente visual encontrado nas proximidades do rio, as condições locais de ruído não eram nada favoráveis aos ciclistas. Em termos de comparação, porém, a seção mais ruidosa da outra rota é ainda pior. Além dos altos níveis de exposição ao ruído, a área é insegura e pouco agradável para os ciclistas devido à circulação em condições de tráfego misto. Por outro lado, é convenientemente localizado em termos de acessibilidade, o que mostra uma vez mais a complexidade envolvida no processo de planejamento de novas infraestruturas cicloviárias. / Although many Brazilian cities are gradually implementing cycling infrastructures, the cyclists\' exposure to noise is not yet seen as an element to be considered in the planning process. With this assumption as a starting point, the objective of this study is to assess cyclists\' exposure to noise in São Carlos, SP, a Brazilian medium-sized city in which around 244,000 inhabitants, 107,000 cars and 25,000 motorcycles were counted in 2016. The study involved the following procedures: i) preliminary definitions and adjustments regarding the data collection campaigns, ii) data collection, iii) data validation, iv) calculation of noise exposure levels, and v) assessment of cyclists\' exposure to noise. Two routes have been analyzed. The first one had dedicated cycling infrastructure, i.e., cycleways and cyclelanes, in some of the 12 sectors considered for analysis. The second route was split in two sectors, both without dedicated cycling infrastructure but with an excellent potential for attracting cycling trips due to the privileged location of the area in the city. Noise exposure was classified according to the average percentage of Sound Exposure Level (SEL) values above 85 dBA and according to the values of noise pollution levels (Lnp). In general, all sections of the two routes were classified as either \"very high\" or \"high\" regarding the cyclists\' exposure to noise, and 3 out of the total 14 sectors were classified as unhealthy. Furthermore, even the sections with the lowest noise exposure levels had nearly half of the data collection trips classified as \"very high\". It is important to highlight that the local environment of the noisiest parts of the 2 routes had different characteristics. The noisiest sections of the first route were registered in a cycleway located along a wide avenue that follows a river surrounded by green areas, but where the posted speed limit for cars is 60 km/h. There is clearly a conflict here, given that despite the safe circulation conditions provided by the cycleway and the pleasant visual environment found nearby the river, the local noise conditions were not at all favorable to cyclists. In terms of comparison, though, the noisiest section of the other route is even worst. In addition to the high levels of noise exposure, the area is unsafe and not very pleasant to cyclists due to the circulation in mixed traffic conditions. On the other hand, it is conveniently located in terms of accessibility, what shows once more the complexity involved in the process of planning new cycling facilities.

Embora muitas cidades brasileiras estejam gradualmente implementando infraestruturas cicloviárias, a exposição dos ciclistas ao ruído ainda não é vista como um elemento a ser considerado no processo de planejamento. A partir deste pressuposto, o objetivo deste estudo é avaliar a exposição dos ciclistas ao ruído em São Carlos, SP, cidade média brasileira na qual cerca de 244 mil habitantes, 107 mil carros e 25 mil motocicletas foram contados em 2016. O estudo envolveu os seguintes procedimentos: i) definições preliminares e ajustes relativos às campanhas de coleta de dados, ii) coleta de dados, iii) validação de dados, iv) cálculo de níveis de exposição ao ruído e v) avaliação da exposição dos ciclistas ao ruído. Foram analisadas duas rotas. A primeira apresentava infraestrutura cicloviária (ciclovias ou ciclofaixas), em alguns dos 12 setores considerados para análise. A segunda rota foi dividida em dois setores, ambos sem infraestrutura cicloviária, mas com um excelente potencial para atrair viagens de bicicleta devido à localização privilegiada da área na cidade. A exposição ao ruído foi classificada de acordo com a percentagem média de valores de SEL (Sound Exposure Level) acima de 85 dBA e de acordo com valores de Lnp (Nível de Poluição Sonora). De maneira geral, os níveis de exposição dos ciclistas ao ruído foram classificados como \"muito alto\" ou \"alto\" em todas as 14 subdivisões das duas rotas, três das quais foram classificados como insalubres. Além disso, mesmo as seções com os menores valores de Lnp apresentaram quase metade das viagens para coleta de dados classificadas como \"muito altas\". É importante destacar que os locais, das partes mais ruidosas das duas rotas, tinham características distintas. Os trechos mais ruidosos da primeira rota foram registrados em uma ciclovia localizada ao longo de uma avenida larga, que margeia um rio e é cercada por áreas verdes, mas onde o limite de velocidade para carros é de 60 km/h. Há claramente um conflito aqui, dado que, apesar das condições de circulação seguras proporcionadas pela ciclovia e o agradável ambiente visual encontrado nas proximidades do rio, as condições locais de ruído não eram nada favoráveis aos ciclistas. Em termos de comparação, porém, a seção mais ruidosa da outra rota é ainda pior. Além dos altos níveis de exposição ao ruído, a área é insegura e pouco agradável para os ciclistas devido à circulação em condições de tráfego misto. Por outro lado, é convenientemente localizado em termos de acessibilidade, o que mostra uma vez mais a complexidade envolvida no processo de planejamento de novas infraestruturas cicloviárias. / Although many Brazilian cities are gradually implementing cycling infrastructures, the cyclists\' exposure to noise is not yet seen as an element to be considered in the planning process. With this assumption as a starting point, the objective of this study is to assess cyclists\' exposure to noise in São Carlos, SP, a Brazilian medium-sized city in which around 244,000 inhabitants, 107,000 cars and 25,000 motorcycles were counted in 2016. The study involved the following procedures: i) preliminary definitions and adjustments regarding the data collection campaigns, ii) data collection, iii) data validation, iv) calculation of noise exposure levels, and v) assessment of cyclists\' exposure to noise. Two routes have been analyzed. The first one had dedicated cycling infrastructure, i.e., cycleways and cyclelanes, in some of the 12 sectors considered for analysis. The second route was split in two sectors, both without dedicated cycling infrastructure but with an excellent potential for attracting cycling trips due to the privileged location of the area in the city. Noise exposure was classified according to the average percentage of Sound Exposure Level (SEL) values above 85 dBA and according to the values of noise pollution levels (Lnp). In general, all sections of the two routes were classified as either \"very high\" or \"high\" regarding the cyclists\' exposure to noise, and 3 out of the total 14 sectors were classified as unhealthy. Furthermore, even the sections with the lowest noise exposure levels had nearly half of the data collection trips classified as \"very high\". It is important to highlight that the local environment of the noisiest parts of the 2 routes had different characteristics. The noisiest sections of the first route were registered in a cycleway located along a wide avenue that follows a river surrounded by green areas, but where the posted speed limit for cars is 60 km/h. There is clearly a conflict here, given that despite the safe circulation conditions provided by the cycleway and the pleasant visual environment found nearby the river, the local noise conditions were not at all favorable to cyclists. In terms of comparison, though, the noisiest section of the other route is even worst. In addition to the high levels of noise exposure, the area is unsafe and not very pleasant to cyclists due to the circulation in mixed traffic conditions. On the other hand, it is conveniently located in terms of accessibility, what shows once more the complexity involved in the process of planning new cycling facilities.

<p dir="ltr">The design of hardware platform in acoustic sensing is critical. The number and the spatial arrangement of microphones play a huge role in sensing performance. All microphones should be properly processed for simultaneous recording. This work introduces an FPGA-based acoustic transceiver system supporting acoustic sensing with custom acoustic signals. The system contains 16 microphones and a speaker synchronized during sensing processes. The microphones were arranged into an ‘L’ shape with eight microphones on each line for a better resolution of angle estimation on two dimensions. The microphones were placed on a specifically designed PCB to achieve an optimal distance of the half-wavelength of acoustic signals for optimized sensing performance. A microphone interface was implemented on Ultra96-V2 FPGA for handling the simultaneous high-speed data streams. The system features an implementation of full-level data transmission up to the top-level Python program. To evaluate the sensing performance of the system, we conducted an experiment used Frequency Modulated Continuous Wave (FMCW) as the transmitted acoustic signal. The result of evaluation shown the accurate sensing of range, velocity and relative angle of a moving hand on the two dimensions corresponding to the microphone groups.</p>

Heavy load equipment, such as tractors, shovels, cranes, airplanes, etc, often employ fluid power (i.e. hydraulic) systems to control their loads by way of valve adjustment in a pump-valve control configuration. Most of these systems have low energy efficiency as a consequence of pressure losses across throttle valves. Much of the energy is converted into heat energy which can have determinantal effects on component life and the surrounding environment. From an energy efficiency point of view, an ideal hydraulic system is one that does not include any throttling valve. One such circuit is made of a variable pump and motor load (pump/motor configuration). The velocity of the load is controlled by manipulating the pump displacement or by changing the rotary speed of the pump shaft. In such a system, the transient response of the load is often unsatisfactory because it is difficult to quickly and accurately manipulate the pump displacement or change shaft speed. Thus circuit design must be a compromise between the energy efficiency of the pump/motor system and the controllability of a pump/valve/motor combination. One possible compromise is to use a pump-valve configuration which reduces energy losses across the valve. One way to achieve this is by controlling the pressure drop across the valve and limiting it to a small value, independent of load pressure. Based on this idea, a type of hydraulic control system, usually called load-sensing (LS), has recently been used in the flow power area. This type of system, however, is complex and under certain operating conditions exhibits instability problems. Methods for compensating these instabilities are usually based on a trial-and-error approach. Although some research has resulted in the definition of some instability criterion, a comprehensive and verifiable approach is still lacking. This research concentrates on identifying the relationship between system parameters and instability in one particular type of LS system. Due to the high degree of non-linearity in LS systems, the instabilities are dependent on the steady state operating point. The study therefore concentrates first on identifying all of the steady state operating points and then classifying them into three steady state operating regions. A dynamic model for each operating region is developed to predict the presence of instabilities. Each model is then validated experimentally. This procedure, used in the study of the LS system, is also applied to a pressure compensated (PC) valve. A PC valve is one in which the flow rate is independent in variations to load pressure. A system which combines a LS pump and a PC valve (for the controlling orifice) is called a load sensing pressure compensated (LSPC) system. This research, then, examines the dynamic performance of the LSPC system using the operating points and steady state operating regions identified in the first part of the research. The original contributions of this research include: (a) establishment of three steady state operating conditions defined as Condition I, II & III, which are based on the solution of steady state non-linear equations; (b) the provision of an empirical model of the orifice discharge coefficient suitable for laminar and turbulent flow, and the transition region between them; (c) and the development of an analytical expression for orifice flow which makes it possible to accurately model and simulate a hydraulic system with pilot stage valve or pump/motor compensator. These contributions result in a practical and reliable method to determine the stability of a LS or LSPC system at any operating point and to optimize the design of the LS or LSPC system.

Heavy load equipment, such as tractors, shovels, cranes, airplanes, etc, often employ fluid power (i.e. hydraulic) systems to control their loads by way of valve adjustment in a pump-valve control configuration. Most of these systems have low energy efficiency as a consequence of pressure losses across throttle valves. Much of the energy is converted into heat energy which can have determinantal effects on component life and the surrounding environment. From an energy efficiency point of view, an ideal hydraulic system is one that does not include any throttling valve. One such circuit is made of a variable pump and motor load (pump/motor configuration). The velocity of the load is controlled by manipulating the pump displacement or by changing the rotary speed of the pump shaft. In such a system, the transient response of the load is often unsatisfactory because it is difficult to quickly and accurately manipulate the pump displacement or change shaft speed. Thus circuit design must be a compromise between the energy efficiency of the pump/motor system and the controllability of a pump/valve/motor combination. One possible compromise is to use a pump-valve configuration which reduces energy losses across the valve. One way to achieve this is by controlling the pressure drop across the valve and limiting it to a small value, independent of load pressure. Based on this idea, a type of hydraulic control system, usually called load-sensing (LS), has recently been used in the flow power area. This type of system, however, is complex and under certain operating conditions exhibits instability problems. Methods for compensating these instabilities are usually based on a trial-and-error approach. Although some research has resulted in the definition of some instability criterion, a comprehensive and verifiable approach is still lacking. This research concentrates on identifying the relationship between system parameters and instability in one particular type of LS system. Due to the high degree of non-linearity in LS systems, the instabilities are dependent on the steady state operating point. The study therefore concentrates first on identifying all of the steady state operating points and then classifying them into three steady state operating regions. A dynamic model for each operating region is developed to predict the presence of instabilities. Each model is then validated experimentally. This procedure, used in the study of the LS system, is also applied to a pressure compensated (PC) valve. A PC valve is one in which the flow rate is independent in variations to load pressure. A system which combines a LS pump and a PC valve (for the controlling orifice) is called a load sensing pressure compensated (LSPC) system. This research, then, examines the dynamic performance of the LSPC system using the operating points and steady state operating regions identified in the first part of the research. The original contributions of this research include: (a) establishment of three steady state operating conditions defined as Condition I, II & III, which are based on the solution of steady state non-linear equations; (b) the provision of an empirical model of the orifice discharge coefficient suitable for laminar and turbulent flow, and the transition region between them; (c) and the development of an analytical expression for orifice flow which makes it possible to accurately model and simulate a hydraulic system with pilot stage valve or pump/motor compensator. These contributions result in a practical and reliable method to determine the stability of a LS or LSPC system at any operating point and to optimize the design of the LS or LSPC system.