Radiômetro solar de equivalência elétrica com sensor aquecido à diferença de temperatura constante.

Abstract

For the measurement of physical quantities, such as radiation, H, velocity fluids, v, and temperature, Ta, there are settings based on thermoresistive sensors, which use the principle of electrical equivalence. Among the classic architectures, which have better frequency response and use this principle, the most common is the one that uses a thermoresistive sensor heated to a constant temperature. The sensor is heated by Joule effect to a previously stipulated temperature, and the variation of thermal radiation, temperature or flow velocity of the medium is compensated by varying the electric heating due to the negative feedback used, maintaining the sensor at an almost constant temperature. In this work it is proposed an alternative architecture that makes constant the temperature difference between the sensor and the environment. For both configurations, in this work, were developed expressions and simulations held for the output signal as a function of the input and the sensitivity of architecture with analog outputs and pulsed (modulated pulse duration - PWM) for sensors types of PTC and NTC. Comparisons were made between the architectures, verifying that architectures with constant temperature difference, analog output and thermoresistive sensor PTC had better performance with respect to the sensitivity, the less influence of interfering variable and the greater influence of input variable.