The Study Of The Two Extension Leads Connection Capacitance Vortex-Type Flow Transmitter

With the fast technological change, flow detection have wide application in control and measurement aspect of the petro-chemical industry. Because capacitance vortex flow-meter has good characteristics of high sensitivity, strong vibration resistance, and convenient installation, it has a wider application range and higher potential among variable flow-meters. However, it still has its own shortcoming such as low measurement precision, power consumption and measurement dead zone. As a result, it is of vital significance to study the two extension leads connection capacitance vortex-type flow transmitter.This thesis first introduces the features and recent research of various flow-meters at home and abroad. Secondly, the mathematical models of differential switching capacitor vortex flow-sensor and charge amplifier are founded. Lastly, based on the mathematical models, the relationship of vortex force and deflection angle of sensing element is emphasized, and a method how decrease the measurement dead area is proposed.Based upon the theoretical analysis, a general systemic design scheme has been proposed. The core of the system is ultra-low power MCU MSP430F149 and new type DAC AD421 with the function of Loop-Powered. The C/V translation circuit, shaping filter, man-machine interface circuits and HART communication circuit are introduced in detail. According to the different function about MCU, the sub routine of measuring frequency, display information, key dealing and HART communication are described respectively.Because of the restrictions of actual conditions, part circuit experiment is carried out. The results show that the system has characteristics of low-power consumption, high measurement precision, wide measurement range, nice linearity and high anti-interference ability.