Conversor Sigma-Delta Térmico com ajuste automático da faixa de operação para medição de radiação incidente

Abstract

The incident thermal radiation measurement, including infrared and solar radiation, has several applications and increasing demand. In the infrared (IR) radiation measurement, resistive microbolometers are the most used sensors, being applied in complex thermal imaging and detection systems. Some researches aim to increase the sensitivity of IR detection systems, as well as to integrate new functions such as analog-to-digital conversion, together with sensors. The measurement of solar radiation has as main applications the meteorology, photovoltaic plants and studies for agriculture, being the pyranometer the most used instrument. Thermoresistive sensors have been used to measure temperature, fluid speed and direction and radiation. In several architectures the sensor operates in closed loop, increasing the sensitivity, decreasing the response time and linearizing the system‘s response. The most used closed-loop architectures are the Wheatstone feedback bridge, control systems, capacitive coupling feedback and Thermal Sigma-Delta Modulator (TΣ∆M). TΣ∆M is a closed-loop measurement approach where the sensing element performs part of the Σ∆ modulation in the thermal domain. A new architecture is proposed in this work for measuring thermal incident radiation using TΣ∆M and thermoresistive sensors, where the modulator input range is automatically adjusted to fit the complete thermal radiation range. The proposed architecture is compared with a similar one, which uses the same transducer interface circuit but without range adjustment, and is validated experimentally with a reference pyranometer. The proposed architecture has the main advantage of presenting a signal-to-noise ratio, and sensitivity, which are independent of the ambient temperature range definition. Experimental results for ambient temperature range of 45 ◦C show a signal-to-noise ratio gain of 13 dB over the state of the art architecture.