S. Casans

Design of a virtual instrument for water quality monitoring across the Internet

Abstract This article presents the design of a new distributed and multi-platform system for water quality monitoring, enhanced with powerful Internet capabilities. The measured variables are temperature, turbidity, pH, dissolved oxygen, and electrical conductivity. The signal-conditioning block has been simplified through the use of software routines for thermal compensation, hence, reducing the cost and dimensions. The system offers a wide variety of Internet capabilities, like e-mail alarm notifications, automatic storage of measured data in a remote machine via the FTP protocol, dynamic generation of HTML reports, real time graphs, and indicators visible from a remote web browser, etc. The whole system supports several types of computers, operating systems and communications hardware. Human presence near the geographic location of water is dramatically reduced, since the system automates the principal tasks of the classical water monitoring process.

Novel voltage-controlled conditioning circuit applied to the ISFETs temporary drift and thermal dependency

This paper describes a novel conditioning circuit applied to ion-sensitive field-effect transistors/membrane-ion-sensitive field-effect transistors (ISFETs/MEMFETs) sensors. The novel conditioning circuit allows the sensor polarization with the needed either voltage or current required in each application, thanks to two completely independent voltage-controlled blocks (current and voltage blocks). The control of the voltage block is the most critical point in our design because the voltage block maintains the sensor feedback stable, avoiding the thermal and temporary drifts of the sensor feedback.

Novel constant current driver for ISFET/MEMFETs characterization

Abstract In the present work a new constant current driver for ISFETs and MEMFETs sensors has been developed. The proposed circuit maintains the ISFET/MEMFET operation point at constant drain–source current and voltage. The combination of some programmable current sources and an appropriate selection of a simple precision resistor allow a good ISFET/MEMFET polarization. The use of operational amplifiers with low offset and drift are required to provide the buffering function needed by the sensor.

Distributed virtual instrument for water quality monitoring across the Internet

This paper shows the design of a distributed and multi-platform system for water quality monitoring, enhanced with Internet capabilities. The signal-conditioning block has been reduced in cost and dimensions through the use of software routines for thermal compensation. The measured variables are temperature, turbidity, pH, dissolved oxygen and electrical conductivity. There are several services offered to the user, such as e-mail alarm notifications, automatic storage of measured data in a remote machine via the FTP protocol, dynamic generation of HTML reports, real time graphs and indicators visible from a remote web browser, etc. The whole system supports several types of computers, operating systems and communications hardware.

Characterization of giant magnetoresistance effect based sensors and its applications

Magnetic field measurement constitutes a good method to know some magnitudes related to it. In this work we present the design of an instrumentation system with the aim to characterize several properties of these magnetoresistance sensors. Experimental results derived from the characterization process are shown and various novel measurement and control applications of these sensors are obtained.

Series Sensor Current Loop from a Generalized Impedance Converter Circuit with Reference Current Input

The paper describes the ability of the Generalized Impedance Converter (GIC) to work as a current-to-current converter. In its classical use GIC circuit was employed to simulate inductors in filters. Putting resistances in its structure and a current generator at its input, the GIC acts as a true current amplifier. The topology is analyzed obtaining DC properties and AC transfer functions. Experimental results are also shown demonstrating how GIC circuit with reference current input could implement a current loop to drive a series sensor connection

Sensor Network to Measure Electric Parameters

Present paper covers the design of a sensor network to measure electric parameters taking into consideration that all needed components are available in the market as commercial products. The work is oriented to the integration of these existing devices and to give extra functionalities. The final functionality and the connection among the used components are provided by the software. The present paper gives special consideration to the software structure. The described system becomes a tool to be used for energy efficiency applications

Extending Magnetoresistive AC Transfer Characteristics for Current Measurement

This paper presents an open-loop compensation method in order to improve a commercial current sensor, based on the anisotropic magnetoresistive effect, for applications requiring high bandwidth current measurement. A simple passive differential filter is proposed to extend the open-loop AC transfer characteristic of AMR sensor. The sensitivity and bandwidth of the overall system are discussed by a transfer function analysis. Instrumentation setup and hardware prototype has been developed, and significant test results are shown.

Novel Resistance Measurement Method: Analysis of Accuracy and Thermal Dependence with Applications in Fiber Materials

Material resistance is important since different physicochemical properties can be extracted from it. This work describes a novel resistance measurement method valid for a wide range of resistance values up to 100 GΩ at a low powered, small sized, digitally controlled and wireless communicated device. The analog and digital circuits of the design are described, analysing the main error sources affecting the accuracy. Accuracy and extended uncertainty are obtained for a pattern decade box, showing a maximum of 1% accuracy for temperatures below 30 ∘C in the range from 1 MΩ to 100 GΩ. Thermal analysis showed stability up to 50 ∘C for values below 10 GΩ and systematic deviations for higher values. Power supply Vi applied to the measurement probes is also analysed, showing no differences in case of the pattern decade box, except for resistance values above 10 GΩ and temperatures above 35 ∘C. To evaluate the circuit behaviour under fiber materials, an 11-day drying process in timber from four species (Oregon pine-Pseudotsuga menziesii, cedar-Cedrus atlantica, ash-Fraxinus excelsior, chestnut-Castanea sativa) was monitored. Results show that the circuit, as expected, provides different resistance values (they need individual conversion curves) for different species and the same ambient conditions. Additionally, it was found that, contrary to the decade box analysis, Vi affects the resistance value due to material properties. In summary, the proposed circuit is able to accurately measure material resistance that can be further related to material properties.

An electrical current smart transducer based on PSoC platform and integrated spin-valve sensor with embedded thin film Ruthenium temperature sensor

This work presents an intelligent electrical current sensor that combines a programmable system on chip (PSoC) with a microfabrication of a giant magnetoresistance sensor (GMR) and resistive temperature detector (RTD). Four spin-valve GMR elements configured in a Wheatstone bridge sense the electrical current, while a thin film RTD based on Ruthenium measures the temperature for spin-valve bridge sensitivity thermal compensation. The mixed signal PSoC allows implement in a single chip all electronic circuits needed to design a smart transducer: the spin-valve biasing, conditioning signal, analog to digital converter, digital signal processing and ports for communications. In the experimental results a small thermal study of the spin-valve is reported. The smart transducer digital output is characterized in the range of ±10 A in dc regime as well as 50 Hz ac regime up to 10 A peak.