D. Ramirez

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.

Modeling of Magnetoresistive-Based Electrical Current Sensors: A Technological Approach

The utilization of modeling tools can, in many cases, help us in the design and final prototyping of any sort of sensors. In this paper, we describe a finite-element method (FEM) model applied to a hybrid technology involving a full Wheatstone bridge spin-valve-based electrical current sensor. After validating the model against experimental results, we focus our studies on geometrical aspects of the sensor configuration, in order to detect possible deviations that may have occurred during the fabrication process. In this regard, the characteristics of the behavior of the sensor depending on lateral displacements and inclination are included. Moreover, the frequency response of the sensor is also analyzed, thus enlarging the scope of the model.

Spin-valve current sensor for industrial applications

This work presents an industrial application of a new spin-valve current sensor based on the giant magnetoresistance effect (GMR) and provides a comparison between this sensor and the typical sensor used in these applications, the hall sensor. Experimental results derived from the application of this two sensors in a power application (a bi-directional three-phase rectifier) are shown.

Electrical Characterization of a Magnetic Tunnel Junction Current Sensor for Industrial Applications

The objective of the work was the design of a Wheatstone bridge current sensor using MTJ as magnetoresistive elements. Each one of the four resistances of the bridge consists on 360 MTJ single elements connected in series for improved electrical robustness. A printed circuit board (PCB) was designed with a U-shaped copper trace placed under the PCB maintaining a 1.1 mm separation distance between sensor and trace. A 160% of tunnel magnetoresistance effect in the single junction and a 120% in its corresponding series elements connection has been achieved with a sensitivity of 9.2 Ω/Oe in a 65 Oe linear range. The DC sensor sensitivity in response to an external DC current sweeps of ±10, ±20, and ±30 A gave an average of 9.8 mV/A. The measured AC sensor response in all the tested cases corresponded to a - 3 dB frequency close to 200 kHz. The sensor was submitted to a DC current excursion under different temperatures showing a TC(S) sensitivity temperature coefficient of 0.031%/° C rather lower compared with the spin-valve technology. The work shows that MTJ sensor technology provides a promising tool in the R+D areas of power management and energy consumption like electric vehicles or energy metering.

Giant magnetoresistive sensor in conductance control of switching regulators

The objective of the present work is to use sensors based on the giant magnetoresistance effect to measure the current generated by a switched mode power supply (SMPS). The sensor is placed within a conductance control loop and its properties influence the dynamic properties of the system. Experimental results are also presented.

MgO Magnetic Tunnel Junction Electrical Current Sensor With Integrated Ru Thermal Sensor

Full Wheatstone bridge electrical current sensor incorporating 114 MgO-based magnetic tunnel junction elements (3 × 30 μm2) connected in series was produced for improved electrical robustness. To that end, magnetic tunnel junctions with R × A ~7 KΩ μm2 tunneling magnetoresistance of 200%, were produced. The sensor was designed with an integrated Ru thin film resistive thermal detector (RTD) for temperature drift monitoring and compensation. In order to achieve a full bridge signal, a U-shaped copper trace was placed under a printed circuit board (PCB) specifically designed for this type of device. The resulting device exhibit sensitivities of 63.9 V/Oe/A in a 75 Oe linear range biased with 1 mA current, providing a significantly advantageous alternative to AMR and GMR based bridges.

Electrical Isolators Based on Tunneling Magnetoresistance Technology

An analog isolator device, based on linear magnetic tunnel junctions is presented. Elemental single structures and full Wheatstone bridge devices are designed, fabricated and tested. In addition, the ranges of functionality of the devices are analyzed, mainly in terms of linearity, signal reconstruction and frequency response.

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.