Absorbance based light emitting diode optical sensors and sensing devices

The ever increasing demand for in situ monitoring of health, environment and security has created a need for reliable, miniaturised sensing devices. To achieve this, appropriate analytical devices are required that possess operating characteristics of reliability, low power consumption, low cost, autonomous operation capability and compatibility with wireless communications systems. The use of light emitting diodes (LEDs) as light sources is one strategy, which has been successfully applied in chemical sensing. This paper summarises the development and advancement of LED based chemical sensors and sensing devices in terms of their configuration and application, with the focus on transmittance and reflectance absorptiometric measurements

A Multi-sensor chip for monitoring the quality of drinking water

A MEMS based multi-sensor chip has been developed for the purpose of monitoring turbidity, TDS, and temperature in a sample of drinking water. The benefits of MEMS technology over conventional sensors include compact size, low power consumption, integration capability, and low cost bulk manufacturing. Two revisions of the multi-sensor silicon chip were designed, fabricated, and tested. The layout of the chip and the fabrication process were redesigned in the second spin to provide more robust and sensitive responses. The sensor structures include photodiodes, temperature diodes, interdigitated electrodes in direct contact with the sample, and capacitive interdigitated fingers. The sensors were characterized with the use of commercially available thermometers, turbidity standard solutions, and TDS standard solutions. Signal conditioning circuitry was implemented to convert each sensor output to a DC level between 0 and 1 V. The sensors were shown to be responsive to temperature, turbidity, and TDS in the ranges applicable to drinking water, although obstacles relating to reliability and signal conditioning still remain

First wide-angle view of channelized turbidity currents links migrating cyclic steps to flow characteristics

Field observations of turbidity currents remain scarce, and thus there is continued debate about their internal structure and how they modify underlying bedforms. Here, I present the results of a new imaging method that examines multiple surge-like turbidity currents within a delta front channel, as they pass over crescent-shaped bedforms. Seven discrete flows over a 2-h period vary in speed from 0.5 to 3.0 ms−1. Only flows that exhibit a distinct acoustically attenuating layer at the base, appear to cause bedform migration. That layer thickens abruptly downstream of the bottom of the lee slope of the bedform, and the upper surface of the layer fluctuates rapidly at that point. The basal layer is inferred to reflect a strong near-bed gradient in density and the thickening is interpreted as a hydraulic jump. These results represent field-scale flow observations in support of a cyclic step origin of crescent-shaped bedforms

Principle and implementations of a refracto-nephelo-turbidimeter for seawater measurements

International audienceSalinity and turbidity are two important seawater properties in physical oceanography. The study of physical oceanography requires a compact high-resolution in-situ salino-turbidimeter to measure these two parameters in different ocean zones. Refractometry has proved to be an effective method to measure seawater salinity with a high resolution. Previous studies have shown that the transmission and scattering of light in a turbid medium impact the light beam deviation measurements, which makes the combination of salinity and turbidity measurements with the same sample mandatory. In this paper, we analyze the requirements and challenges of a refracto-turbidimeter design from their measurement principles and correlations. According to these requirements, we propose a miniature refracto-nephelo-turbidimeter with a CCD, providing a salinity measurement resolution of 2 mg.kg-1 and a turbidity measurement resolution of 1 % of the measurement range. Based on this refracto-nephelo-turbidimeter, different embodiments are discussed to meet the different requirements for different ocean zones

Integrating cavity based gas cells: a multibeam compensation scheme for pathlength variation

We present a four beam ratiometric setup for an integrating sphere based gas cell, which can correct for changes in pathlength due to sphere wall contamination. This allows for the gas absorption coefficient to be determined continuously without needing to recalibrate the setup. We demonstrate the technique experimentally, measuring methane gas at 1651nm. For example, contamination covering 1.2% of the sphere wall resulted in an uncompensated error in gas absorption coefficient of ≈41%. With the ratiometric scheme, this error was reduced to ≈2%. Potential limitations of the technique, due to subsequent deviations from mathematical assumptions are discussed, including severe sphere window contamination

A fast method for mobile in-situ monitoring of optical properties in aquatic environments

In summary, this dissertation presents a fundamental sensor development according to newly formulated sampling theorem (Object Specific Exposure - OSE) from an ocean engineering perspective. It provides a fast method based on a service-oriented optical sensor system that allows reliable statements regarding the state of aquatic (eco-) systems (turbidity and dissolved organic carbon) with feasible sensor effort during the field measurement. The technological approach presented in this thesis helps to increase the informative value of sensor data while reducing the effort for the user.Zusammenfassend stellt diese Dissertation eine grundlegende Sensorentwicklung nach einem neu formulierten Monitoring-Theorem (Object Specific Exposure - OSE) aus meerestechnischer Sicht dar. Vorgestellt wird eine Methode, die auf Basis eines serviceorientierten optischen Sensorsystems Aussagen über den Zustand von aquatischen (Öko-) Systemen (Trübung und Gehalt gelöster organischer Verbindungen) mit geringem methodischen Sensoraufwand im Feld ermöglicht

Design and implementation of control system for optimal growth of microalgae in outdoor ponds

Over the last decade or so, extensive research has taken place in the field of microalgae for the production of biomass, bio fuels and waste water treatment. With the evolution and versatility in biotechnology, microalgal biomasses have been treated industrially for food, pharmaceutical, nutraceutical and animal feed besides other high-value bio products beneficial for mankind. Microalgae can be cultivated in open systems such as open raceway ponds or closed systems such as photobioreactors (PBR). The conditions for growth in the PBRs are tightly controlled for maximum algal biomass production; however, it comes with associated cost. Although, it is far less costly for growing microalgae outdoor open ponds, the conditions are uncontrolled and hence growth remains compromised due to environmental factors. There are several variables responsible for the growth of microalgae both indoor and outdoor. This thesis documents the strategy for controlling one of the important parameters of growth, i.e., the temperature of an outdoor pond around an optimal temperature range. Different sensors were used in the system to measure the parameters of the same culture in two different ponds, however, only temperature was manipulated in one of the ponds and its growth was compared with the other pond where all the variables were left unaltered. A Proportional Integral controller was implemented for the purpose of controlling the temperature at the required hours of the day. Several tests were conducted to check the performance of the controller before the controller was deployed. A user interactive LabVIEW application was developed keeping in view the requirements of the user, which also included data storage functionality. As a result of the experiment, it was observed in the various harvests of the culture that there is an increase in the biomass and productivity of the heated pond. The results were statistically analysed to highlight the significance of growth that was observed during the experiments

It\u27s a Small World After All: Insights, Interferences, and Implications of In Situ Chlorophyll Fluorescence Monitoring in Estuaries

Concentrations of the photosynthetic pigment chlorophyll a are used as a proxy for phytoplankton biomass by estuarine scientists to study eutrophication, food web dynamics, and harmful algal blooms. Coastal managers use chlorophyll as an indicator of nutrient pollution and for assessments to meet Clean Water Act standards. Chlorophyll a, as measured in the laboratory by extraction from monthly discrete water samples, is a core component of the National Estuarine Research Reserve (NERR) System-Wide Monitoring Program (SWMP). Field-deployable sensors based on the excitation and emission spectra of in situ chlorophyll have not been incorporated into SWMP to date because past studies showed inconsistencies across reserves. Several studies have shown in situ chlorophyll fluorescence to be temperature sensitive as well as subject to spectral interference from fluorescent dissolved organic matter (fDOM) and turbidity. The project objectives included the assessment of sensor reliability across a range of environmental conditions, identifying interferences that may affect sensor output, and developing estuary-wide or conditional relationships between chlorophyll monitoring using the datasonde and extractive chlorophyll measurements. To achieve these objectives, validation of the sensor output through paired sampling with extractive analysis was conducted. Additional testing focused on identifying sensor interferences was also conducted including temperature, turbidity and fDOM. Results indicate in situ chlorophyll fluorescence correlates to extracted chlorophyll, but this relationship is influenced by the environmental interferences mentioned. Utilizing hierarchical regression modeling to incorporate data from interfering parameters improved the relation between sensor and extracted concentrations. Incorporating this sensor into NERR SWMP long-term water quality monitoring program as a surrogate for chlorophyll concentration will give coastal managers around the country increased insight into what drives the base of estuarine food webs. Combined with satellite telemetry, these sensors provide near-real-time insight into phytoplankton dynamics, with the potential to provide early detection and rapid response to harmful algae blooms

Utilising a fieldbus protocol in a water quality monitoring system

This thesis presents a new water quality monitoring system developed at the University of Durham in conjunction with Partech Instruments Ltd. The system uses a fieldbus protocol to create an open, distributed control network, replacing the dedicated products currently offered. Echelon LonWorks has been used to create three nodes: a suspended solids sensor, a general-purpose interactive monitoring tool, and a universal relay setpoint module. When connected, these nodes provide a means of activating relays when the suspended solids level reaches a definable level, while providing a numerical display for the operator. The sensor may be calibrated for a number of different applications. The sensor uses infra-a-red light to monitor the light absorption and 90 scatter within the solution. By dynamically adjusting the intensity of the emitted light, the sensor is able to increase its range over conventional devices. Signal processing, linearization and calibration operations are carried out within the sensor software. The final measurement is communicated as a LonWorks network variable, allowing the sensor to be treated as an interoperable device. Several third-party products have been connected to the network and a high degree of interoperability demonstrated. Three network management software packages have been investigated, and their suitability assessed. The final prototype system shows the power, flexibility and cost-saving that a fieldbus protocol can provide in an industrial control environment