Sebastian Y. C. Catunda

Maximum-Likelihood Data Fusion of Phase-Difference and Threshold-Detection Techniques for Wind-Speed Measurement

Analyses of threshold-detection and phase-difference techniques for wind-speed measurement using ultrasonic transducers are presented. The influence of uncertainties that are associated with additive noise and attenuation of the ultrasonic signal on the wind-speed measurement uncertainty is analyzed. A data-fusion procedure based on the maximum-likelihood estimation (MLE) algorithm is developed for the determination of wind speed, with data gathered through threshold-detection and phase-difference techniques. The data-fusion procedure provides a lower measurement uncertainty than those obtained with the above techniques when taken separately. Practical design issues are considered, and an application example is shown to illustrate the proposed procedure.

Designing a programmable analog signal conditioning circuit without loss of measurement range

Programmable analog signal conditioning circuits can be programmed in the field to permit their use in several applications with a variety of sensors with different output signal characteristics. The digital programming of the gain and dc level shift of a conditioning circuit can affect the measurement resolution and cause a reduction in the range of the measuring system in which it is employed. For a specified maximum acceptable loss in the measurement resolution, a procedure for defining and employing the programming values that guarantees the full measurement range is proposed. The proposed methodology takes into account practical implementation considerations and can be employed for designing either discrete or integrated circuits.

Applications of Thermoresistive Sensors Using the Electric Equivalence Principle

In this paper, a survey on the characteristics of thermoresistive sensors [positive temperature coefficient (PTC) and negative temperature coefficient (NTC)] and their applications to measurement structures that use the electric equivalence principle, in special radiometers and anemometers, is presented. The dynamic responses of the architectures and the influence of the operational amplifier offset voltage on the instrument performance are discussed. Alternative architectures employing pulsewidth modulation (PWM) and sigma-delta analog-to-digital (A/D) converters are also shown.

DC-Amplifier-Input-Offset-Voltage Control in a Constant-Temperature Thermoresistive-Sensor-Measurement Instrument

In this paper, the effect of dc amplifier input offset voltage on the static and dynamic performances of a generic constant-temperature thermoresistive-sensor-feedback circuit (CTC) is reviewed. A negative-feedback automatic control circuit for the input offset voltage is proposed in order to assure a stable operation of the CTC and to obtain optimal response time. Experimental evaluation results of the proposed circuit performance are presented

FPGA-based SVPWM trigger generator for a 3/spl phi/ voltage source inverter

An FPGA-based space vector pulse width modulator (SVPWM) for use with a voltage source inverter is designed. The modulator is based on the comparison between the reference sinusoidal signals and a triangular carrier waveform. The carrier-based modulation is interpreted in terms of space vector theory. The design permits implementation of predefined modulation strategies and a user-designed strategy. The modulation configuration has been written in Verilog HDL code and typical modulator output pulses for different strategies have been presented.

Look-up table and breakpoints determination for piecewise linear approximation functions using evolutionary computation

Am -Piecewise linear approximalion of nonlinear funclions is a viable design approach for embedded systems withoutfloatingpoint capabilities. In this work, we propose a new procedure for determining the breakpoints posirions and minimam memory necessary for solving this approximation problem, which meets the designs specification accuracy. The LUT memory size is minimized by using a lopdown searching algorithm, which Iries to find a solution for each pair of breakpoints storing resolution and number of breakpoints. An evolutionary algorithm is employed at lhe boaom level for searching the breakpoints positions, considering relevant practical issues. The proposed procedure optimizes the solufion w.r.f the LUT size and breakpoints distribution

Automatic dynamic range adjustment of a controlled-temperature thermoresistive-based anemometer

The thermoresistive-based hot-wire anemometer operating at a controlled temperature is a classical architecture that is vastly found in the literature. Nevertheless, this architecture presents a problem due to dynamic range variation with respect to the fluid temperature. In this work an alternative architecture of a controlled temperature anemometer with automatic adjustment of the dynamic range is proposed. Simulations of the proposed system using the parameters from a commercial sensor are presented and compared with the results from a classical configuration.

Sensitivity analysis and automatic adjustment of a controlled-temperature thermoresistive-based anemometer

This paper presents an architecture of a hot-wire anemometer that adjusts the difference between the sensor temperature and the fluid temperature and maximizes the sensitivity of the output quantity (voltage or pulse width) in relation to the input quantity (velocity). Analyses were made for the PTC and NTC sensors type and for output in pulse width or analog voltage type. It was verified that, for PTC sensors the sensitivity is as higher as the difference between the temperature of the sensor and the fluid temperature. For a NTC, on the other hand, the sensitivity is maximum when the difference of temperature is 30 K (for one commercial sensor parameters).

Wind speed measurement method using ultrasonic sensors with stationary wavelet transform

A method for measuring speed wind, based on echo detection using ultrasonic transducers with stationary wavelet transform is presented. The stationary wavelet transform (SWT) can be obtained by modifying the basic scheme of discrete wavelet transform (DWT). Two filters are applied to produce the output two sequences at each level. Since decimation is not obtained at the exit of each level, sequences of length equal to the original signal. But the filters are changed at each level adding zeros. After obtaining the SWT coefficients, noise removal will be performed using the soft-threshold rule due the coefficients still include the effects of noise. The measured ultrasound signals are processed using the stationary wavelet transform. The accuracy of the extracted information from the processed signal depends on the adopted mother wavelet. To select the best mother wavelet for signal processing, a criterion based on Shannons entropy is used. The influence of uncertainties associated with additive noise and attenuation of the ultrasonic signal on the wind speed measurement uncertainty is analyzed.

Current transformer with nanocrystalline alloy core for measurement

In this paper some considerations about the application of nanocrystalline alloys in toroidal cores for current transformers used for measurement purposes are presented. Based on the electromagnetic properties of these materials, such as high relative magnetic permeability, magnetic flux density saturation, high resistivity and low hysteresis losses are discussed. Also, will be discussed how the former characteristics affect the current transformer performance. From experimental results, it can be concluded that the use of nanocrystalline alloys in the current transformer cores can contribute to the reduction of phase errors, improving thus the accuracy class.