tailieunhanh - Advances in Measurement Systems Part 10

Tham khảo tài liệu 'advances in measurement systems part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 356 Advances in Measurement Systems among two logarithms corresponds to the logarithm of the ratio the signal vout is proportional to the logarithm of the impedance ZI. V 1 LogV -LogV 1 fLogV 1 1 Log VddS Z out 2 2 Vd 2 VDDS 2 R2 1 Z. I2 T . 1 Log Log Z - b 2 R 32 The impedance module of the telemetry system has wide variations and in order to keep the signals into the linear range of each block the Vdds voltage can vary. Moreover Vdds voltage can also slightly change due to problems of nonlinearity or temperature shift of the DDS circuit s output. The logarithmic block according to equation 32 compensates for Vdds change. Furthermore the constant term b of equation 32 can be neglected because the resonant frequencies are evaluated as relative maximum and minimum quantities. The whole system has been tested in the laboratory applied to an inductive telemetric system for humidity measurement several results are reported in the following paragraph 5 . 4. An Inductive Telemetric System for Temperature Measurements In this paragraph an inductive telemetric system measures high-temperature in harsh industrial environments. The sensing inductor is a hybrid device constituted by a MEMS temperature sensor developed using the Metal MUMPs process Andò et al. 2008 and a planar inductor fabricated in thick film technology by screen printing over an alumina substrate a conductive ink in a spiral shape. The MEMS working principle is based on a capacitance variation due to changing of the area faced between the two armatures. The area changing appears as a consequence of a structural deformation due to temperature variation. The readout inductor is a planar inductor too. An impedance analyzer measures the impedance at the terminals of the readout inductor and the MEMS capacitance value is calculated by applying the methods of the three resonances and minimum phase. Moreover the capacitance value of similar MEMS is also evaluated by another impedance analyzer through a direct .