José Sérgio da Rocha Neto

Dynamic response of thermoresistive sensors

Electronic circuit configurations for determining the dynamic response of thermoresistive sensors, using pulsed electrical excitation step and radiation step, are presented. Experimental results obtained with these circuits are included. The reduction in the response time of an instrument with these sensors in feedback structures is experimentally demonstrated. >

Electro-thermomechanical characterization of Ti-Ni shape memory alloy thin wires

The use of shape memory alloys (SMA) as smart structures and other modern applications require a previous evaluation of its performance under load as well as a training procedure. In general, these requirements lead to the design and assembly of a specific test bench. In this work, an experimental set-up was specially designed to perform the electro-thermomechanical characterization of SMA wires. This apparatus was used to determine the strain-temperature (e - T) and electrical resistance-temperature (R - T) hysteretic characteristics curves of a Ti-Ni shape memory wire (90 mm in length and 150 µm in diameter) under mechanical load. The SMA wire is loaded by means of constant weights and a controlled system for injection of electrical power allows performing the heating-cooling cycles. The obtained hysteretic e - T and R - T characteristics curves for some levels of applied loads are used to determine important shape memory parameters, like martensitic transformation temperatures, temperature hysteresis, temperature slopes and shape memory effect under load. These parameters were in accord with the ones found in literature for the studied SMA wires.

Identification of thermo-resistive solar radiation sensors

The authors present an identification procedure to estimate the parameters of a thermo-resistive solar radiation sensor. The proposed technique employs only electrical signals to excite the sensor. The estimation algorithm is recursive and is applied to the sensor model derived from the thermodynamic equilibrum differential equations. The simulation and the experimental results demonstrate the validity of the proposed approach.<<ETX>>

Fouling detection based on analysis of ultrasonic guided waves using wavelet transform

Fouling detection is a relevant problem for chemical, oil, food and pharmaceutical industries. Fouling consists of the deposition of heavy organic materials and other dissolved solids or in suspension in fluid transport system. The ultrasonic guided waves present specific characteristics and have demonstrated good results in detection of flaws in pipelines. In this paper, the application of wavelet transform to analyze ultrasonic signals in order to detect fouling in pipelines is presented. A platform of tests has been used to emulate the fouling problem. The pipelines were used as a medium to guide ultrasonic waves and weekly measurements were used to observe the fouling process. The Daubechies 4 wavelet was applied to each measurement set. The results reveal that the variations of the energy-spectrum of the wavelet detail coefficients may provide an appropriate way to detect fouling, since it was observed that the increase of the fouling causes a notable reduction in the energy values.

Vibration analysis for fouling detection using hammer impact test and finite element simulation

The easy detection of fouling in duct systems is a persistent problem and remains a relevant demand for the chemical, oil, food and pharmaceutical industries. This work presents preliminary research results of vibrational hammer excitation for easy to use external non-invasive, non-destructive fouling detection in pipelines and other large scale duct systems. The main goal is the detection of inner pipe layer formation, and thickness estimation of the adsorbed material. Data were taken from the vibration amplitude variation in presence of an inner pipe fouling layer using acoustic accelerometer detection, combined with FE (Finite Elements). The experimental set-up, achievable sensitivity and limitations of the method are outlined.

Radiometric location of partial discharge sources for the future smart grid

Measurements are reported that suggest partial discharge sources might be detected and located using amplitude-only free-space radiometric measurements. The measurements are made in two locations with similar measurement protocols by three collaborating research groups. One measurement set is more encouraging than the other but a likely explanation for the disparate nature of the results is offered. It is suggested that amplitude only measurements might form the basis of a low-cost wireless sensor network for monitoring partial discharge in electricity substation.

Implementation of a Decentralized PID Control System on an Experimental Platform Using LabVIEW

In this paper, the implementation of a decentralized control system is done on an experimental platform, which is dedicated to the study of fouling in industrial tubes. This plant is modelled as a multivariable system of order 2 × 2, whose the inputs are the voltage and current applied respectively in the plant actuators, and the outputs are flow and pressure measurements obtained by sensors in the main tube. The decentralized PID control system is performed by a supervisory system developed in LabVIEW software to verify the impact of fouling on the current behavior of the experimental platform, and thus enable performing predictive maintenance.

Hammer impact test applied for fouling detection in pipelines

The fouling detection in duct systems is a persistent problem and remains a relevant demand for the chemical, oil, food and pharmaceutical industries. The fouling is a deposition process of heavy organic and other dissolved solid materials in the transported fluids or suspensions onto inner wall surfaces in fluid transport systems. This work presents research results of hammer test for vibration analysis using non-invasive tests to fouling detection in pipelines. Data were taken from the vibration in presence of an inner pipe fouling layer using an accelerometer and a microphone for detection. With the analysis of the obtained results is possible to detect the fouling process, in the monitored pipelines, with and without load conditions, using a microphone and an accelerometer as sensors.

Control of strain in a flexible beam using Ni-Ti-Cu shape memory alloy wire actuators

In this paper the development of an experimental test bench to analyze and control the strain of a flexible aluminum beam subjected to external disturbances is described. In the proposed platform, strain-gauges are used to measure the strain of the beam in a single cantilever mode while Ni-Ti-Cu Shape Memory Alloy (SMA) wires are used as force actuators. Data acquisition and control system are implemented with an ADuC microcontroller. The response of the structure in open-loop was used to identify the mathematical model of the system. To find the appropriate controller and to reach the best performance of the system, it was used techniques of direct tuning (pole-zero cancellation) in the identified model. The PI controller has been used to control the strain of the beam for different types of reference signals, as square, sinusoidal and triangular. The frequencies of the reference signals have been varied to observe to which bandwidth the system can respond. Experimental results are used to demonstrate the usefulness of the PI controller in the proposed smart structure.

Compensation of self-heating in the measurement of the dynamic response of a thermoresistive sensor

In the experimental determination of the response time of a thermoresistive sensor to a radiation step, one needs to monitor the variation of the ohmic resistance of the sensor with time. This requires passing electrical current through the sensor, which introduces error in the measured response time due to the additional self-heating of the sensor by the electrical current. A theoretical method to eliminate this error is formulated and experimental results are presented. The proposed method also permits experimental determination of the heat capacity (mc) and heat transfer coefficient (UA). The sensitivity analysis of {tau} = mc/UA permits the optimal choice for the resistance measurement currents.