J.C. Campo

A Discharge Lamp Model Based on Lamp Dynamic Conductance

A model for discharge lamp based on lamp electrical conductance is proposed. Physical assumptions are used to obtain this model. The model allows simulating lamp behavior at different frequencies and delivered power levels. The model has been verified using a high pressure sodium lamp supplied at 50 and 100kHz

Dual-tap chopping stabilizer with mixed seminatural switching. Analysis and synthesis

Onload tap changers based on silicon-controlled rectifiers or triacs are widely used to regulate ac voltage. Response time is bigger than half-cycle due to the natural commutation used during the zero-current crossing. N. Burany proposed a commutation method for direct ac/ac matrix converters based on power transistors, or other switches with active turn-off, by permitting a freewheeling current path during commutation. This can be applicable to tap changers and release commutation from the zero-current crossing, thus allowing a faster voltage regulation. This paper presents a new two-tap chopped ac/ac voltage stabilizer with compensating transformer and PWM frequency in the order of 5 kHz based on this kind of commutation. The circuit proposed, resulted from a topology search guided by an iterative analysis+synthesis cost comparative method, fits well to low voltage stabilizers and regulators in the range of 0.1 to 1000 kVA and 1 ms response time. The switching behavior and the input and output filtering is fully analyzed. An exhaustive synthesis study follows, giving the component rates as a function of the equipment specification. This allows an easy equipment cost evaluation. Experimental results with IGBT switches are obtained in a 1 kVA prototype.

Design of a Low-Cost Portable Potentiostat for Amperometric Biosensors

This work shows the design of a low-cost, portable instrument for amperometric biosensors, which measures the faradaic currents originated by the electronic interchanges between a specific substance and a biological recognition system, present on an electrode and kept at an appropriate potential. The final objective is to obtain a direct relationship between those currents and the concentration of the substrate to be analyzed. This instrument may be used for sensors or cells with two or three electrodes in order to detect extremely low concentrations of a wide variety of substances. The instrument was evaluated comparing calibration curves from glucose, ethanol and cholesterol biosensors to those obtained from very expensive commercial equipment. Good linearity and sensibility, as well as low noise measurements were obtained. Moreover, thanks to its reduced size and low cost, this instrument can be used directly in field applications

Accurate detection algorithm of battery full-capacity under fast-charge

The expanding number of battery portable products has widely increase the use of sealed NiCd/NiMH batteries. Battery fast-charge (in less than one hour) is very useful but, in fast-charge, cell pressure and temperature increase quickly during overcharging (after the battery reaches full-charge). Usual fast-charge end methods do not avoid the overcharge or they require complex calculation processes. In this paper, a new fast-charge end method is proposed. This method is based on a simple and easily implemented algorithm and it allows us to know accurately and reliably the moment when the battery reaches full-capacity. In this way, a safe fast-charge without negative effects on the effective capacity of the battery and on battery cycle-life is guaranteed.

The influence of surface coating on the properties of water-soluble CdSe and CdSe/ZnS quantum dots

It is well-known that ligands coating the surface of luminescent semiconductor nanocrystals (quantum dots [QDs]) play an important role in the preparation, stability and physical properties of the colloidal QDs in both organic and aqueous media. Here we report on the synthesis and characterization of core (CdSe QDs) and core–shell structured QDs (CdSe/ZnS QDs), both of them stabilized in aqueous medium through different mechanisms of modification of their surface chemistry. The approaches evaluated for QDs transfer to aqueous media were ligand exchange and polymer coating. Experiments were performed using two typical thioalkyl acids as ligands, namely mercaptoacetic acid (QDs-MAA) and 2-mercaptoethanesulphonic acid (QDs-MES), and an amphiphilic polymer (PQDs) based on poly(maleic anhydride) functional groups. The effects of pH (buffer solution), illumination and the presence of ions in the QD environment on the spectroscopic properties of the different synthesized QDs are reported. The stability of the prepared QDs has been comparatively evaluated aimed to elucidate which surface chemistry provides the suitable properties to be employed as fluorescence labels in distinct types of applications. The experimental results and conclusions will be useful for the development of sensitive sensors or assays adopting QDs as fluorescence labels.

Low-cost system based on electro-oculography for communication of disabled people

This paper describes a new low-cost real-time communication assistive system for disabled people, especially those with only eye-motor coordination. The retinal resting potential causes an electric field around the eyeball, centred on the optical axis, which can be measured by placing electrodes near to the eye. An acquisition system was implemented for measuring this potential in order to detect the movement of the eyes and to provide a relative gaze position, making it possible to codify ocular actions as commands. A human-computer interface (HCI) to control the mouse and a virtual screen keyboard, that offers simple setup combined with high performance, have also been developed. This device has multiple applications, especially in assistive research, where control is governed by means of the ocular position (eye displacement in its orbit). The theory behind the device and the hardware and software design of the system are presented.

Design of a low cost mastitis detector in cows by measuring electrical conductivity of milk

Mastitis in cows is an inflammation of the mammary gland usually caused by bacterial infection of udder tissues. This disease causes considerable damage to the cattlemen whilst reducing the quantity and the quality of the produced milk. An early detection and corrective action can lead to early cure. Although the universal method to measure mastitis levels is by determining the somatic cell counts per milliliter of milk, the electrical conductivity of milk is a rapid test for checking the acceptability of milk to monitor the effects of udder infection. This work presents the design of a low cost mastitis detector in cows using ac conductivity measurements.

Design of a multi-parameter substance analyzer

In this paper a low-cost new system for multiple measurement of several substances is presented. Principle of operation is based in light analysis of chemical sensor phosphorescence emission. Fiber optics are used to guide the excitation and emission light, extending the possibilities of the instrument and allowing us to obtain excellent characteristics: high sensitivity and linearity, high precision and low maintenance cost.

A new low-maintenance, low-cost optical system to measure low level oxygen concentrations by using avalanche photodiode (APD)

In this paper, a very simple and low-cost photodetection system is presented which can be used for measuring very low oxygen concentration in gaseous medium based on the phosphorescence lifetime of Al-Ferron in a sol-gel probe. A similar system has been presented by other authors but the most innovative aspect in this work is the use of an Avalanche Photodiode (APD). The APD has several important advantages over photomultiplier tubes (PMTs) such as a lower device size, low cost and less critical power supply requirements. The APD has a good photosensitivity and low dark current, sufficient characteristics for measuring phosphorescence.

Measurement of air moisture by the phosphorescence lifetime of a sol-gel based sensor

Air moisture is an important parameter in several industrial processes. Most of the sensors to measure air moisture are based on changes of the electrical properties of some materials. There are also optical sensors based on changes in the color and infrared sensor based on the high absorption of the water compared to other substances. In this paper, we present another type of optical sensor based on the measurement of phosphorescence lifetime of Al-Ferron in sol-gel support and using optical fibers to guide the light. The performance of the sensor has been evaluated by passing different wet streams through the sensor.