Development Of Low-power Two-wire Coriolis Mass Flow Transmitter

Coriolis mass flowmeter based on the Coriolis force principle can directly measure the mass flow of the fluid,is not affected by the external temperature and pressure,and has high measurement accuracy and good repeatability.The two-wire flowmeter has advantages,such as low product cost,strong anti-interference ability of the current loop,the communication line providing power for the flowmeter,and being used in flammable and explosive occasions.It is one of the commonly used instrument types in industrial sites.Coriolis mass flowmeters not only need to maintain the continuous and stable vibration of the flow tube,but also need to process the sensor output signal and calculate the mass flow rate at high speed and accurately.Therefore,the power consumption of the transmitter is high,and it is difficult to achieve a low-power and two-wire system.At present,only famous foreign instrument companies have developed low-power two-wire Coriolis mass flowmeters.There are no such products and research results developed by China.To this end,we develop a low-power two-wire Coriolis mass flow transmitter.A hardware system based on STM32 microcontroller is developed,which consists of a signal conditioning module,a drive module,a data processing module,a communication module,a temperature compensation module,a safety barrier module and a power management module.The difficulties in the design are studied in depth,including drive mode,power distribution and power management,and solutions are proposed.The semidigital drive mode is designed by STM32 microcontroller,and the drive structure is improved to reduce the number of chips used in the drive circuit.Adopting 12?20m A loop power supply technology similar to Emerson's Micro Motion 2200 S transmitter,12 m A is used for meter operation,and 12?20m A is used for communication.The “DC / DC + LDO” power supply structure is adopted: a DC/DC conversion is used to reduce 24 V to slightly higher than the required voltage for improving power conversion efficiency,and then a LDO conversion is used to convert the slightly higher voltage to the required voltage for ensuring the stability of the power supply.An orthogonal demodulation algorithm is studied for Coriolis mass flowmeter.The single-cycle finite point data cycle call of the demodulation signal is realize by using the periodic characteristics of the sinusoidal signal to improve the measurement accuracy and reduce the amount of algorithm calculation.A second-order FIR notch filter filters out the high-frequency components of the demodulated signal,and then a second-order IIR filter is ultized to filter out the noise components.The STM32 microcontroller is used to realize the quadrature demodulation signal processing method in real time,and two-level averaging is added to the post-processing of the phase difference,so as to eliminate the outliers and reduce the steady-state volatility.A software systems is developed by using the modular programming,mainly including a main monitoring program,an initialization module,an algorithm module,a signal acquisition module,a LCD display module,an interrupt module,a watchdog module,etc.The signal acquisition module is responsible for communicating with the ADC to collect two sensor signals.The timer 1 interrupt module is responsible for completing 4?20m A current output and pulse output.In order to verify the effectiveness of the two-wire Coriolis mass flow transmitter,the transmitter was matched with the micro-bend Coriolis mass flow sensor of Shanghai Yinuo Instrument Co.,Ltd.to form a complete Coriolis mass flowmeter,and the power consumption test and water flow calibration experiments were performed.The power consumption test results show that the current of the flowmeter during normal operation is 10.7880 m A,and the overall power consumption is less than 12 m A,which meets the two-wire system requirements of the Coriolis mass flowmeter.The experimental results of water flow calibration show that within the range ratio of 12: 1,the error of water flow calibration is within ± 0.1%,and the repeatability is within 0.05%,which is better than the requirements of "JJG1038-2008 Coriolis Mass Flowmeter Verification Regulation" for the 0.1-level accuracy Coriolis mass flowmeters.