Research On Integrated Metal Tube Rotameter Based On Magnetoresistive Sensors

Flow is a primary parameter to be measured and controlled in Process control, medical, energy metering and other fields in the daily life. Rotameter is a kind of classical variable area flow meter. It is widely used in gas, liquid, steam flow measurement due to its simplicity, low price, high stability and low pre-straight pipe and post-straight pipe Requirements.This thesis is about the research of integrated metal tube rotameter, which is based on magnetoresistive sensors and microcontroller MSP430. In practice, the vertical displacement of the floater is converted into the angular displacement of external magnetic cylinder by magnetic coupling. The magnetic angle is detected by magnetoresistive sensors, the ambient temperature is detected by temperature sensor and the pressure and temperature of the measured fluid are detected by pressure and temperature sensors. They were achieved to sample, process software algorithms, putout PWM wave, display the measure flow by MSP430. They were completed to calibrate rotameter and set lower machine parameters by the RS485 standard communication interface. In addition, external watchdog and power-down protection circuit module were added in the system in order to improve reliability.In order to meet factual demands, this paper designed two programs. One was powered by 24V DC and included RS485 communication transceiver port. The other was powered by 3.6V battery.The software of microcontroller MSP430 was modular designed,including modules such as flow signal acquisition and calculation, Instantaneous flow/total flow rate display, PWM wave output, upper and lower machine communication, instrument parameters storage, etc. Furthermore, these modules were optimized in the main program.This paper analyzed what were caused linearity of rotameter calibration curve and made use of Division Ordinary Least Squares Correction Algorithm to solve measurement accuracy declining due to the linearity of rotameter calibration curve. By the algorithm comparative experiment, it could be proved that the method could improve the measurement accuracy.According to this design, two prototypes in different sizes were built and calibrated. Experimental results demonstrated 1.0% measuring precision ratio of the metal tube rotameter.