Wireless Measurement Electronics for Passive Temperature Sensor

High-temperature measurement systems do not allow the use of traditional measurement techniques. In the presence of high temperatures, the proper functioning of electronics is compromised. Furthermore, if the measurement environment is also hermetic, the traditional cabled measurement technique cannot be adopted. In this paper, a system composed by a passive sensor placed in the harsh environment and a dedicated readout electronics placed outside in a safe zone is designed and proposed for measuring the temperature up to 330°C. The sensing element is based on a hybrid sensor constituted solely by passive components (an inductor connected to a planar micromachined variable capacitor). The hybrid sensor can be placed inside high-temperature and hermetic measuring environment, while the temperature data can be measured telemetrically by an external reading unit, located in the safe environment. In this paper, the system is presented using novel electronic circuits of the readout unit, which permit to avoid the need of an expensive commercial impedance analyzer. The wireless measurement electronics was designed and characterized; the results obtained and reported in this paper are quite in good agreement with those measured by a reference commercial impedance analyzer. The complete measurement system is presented as a viable solution to the measurement of high temperatures in harsh or enclosed industrial environments.