Research On On-Line Monitoring System Of Liquid Density In Pipeline

Pipeline transportation is an important way to realize long-distance transportation of liquid materials.Density,as one of the physical parameters of liquids,is currently widely used in industrial production,scientific research,and so forth.In the process of liquid pipeline transportation,density can be used to solve practical problems such as liquid quality detection and multi-liquid transportation and ensure the efficiency and safety of the transportation process.To this end,this paper has developed a set of on-line detection system for liquid density inside the pipeline.It uses a vibrating straight tube sensor based on the principle of resonance density measurement to detect the liquid density in real time and on-line.The resonant tubular density meter developed in this subject will be used to detect the pipeline transportation of petroleum,and can also take into account the density of other liquids.This article mainly starts from several parts such as the measurement principle,hardware circuit,software design,instrument calibration and calibration of the resonant tube densitometer.The specific research content is as follows:It introduces the measurement principle of the vibrating tube liquid density measurement method,theoretically deduces calculating the frequency of the vibrating straight tube and the relationship with the density in detail and the characteristics of the resonance frequency of the vibrating straight tube are also analyzed.The modal analysis of ANSYS software is used to simulate the core component of the vibrating tube,and analyze the vibration law and influencing factors of the vibrating tube from the aspects of structure size,straight tube shape and temperature.Through theoretical simulation,the 7835 type vibrating single straight tube is determined as the core component of the sensor.Based on the selected sensor,an online liquid density measurement system was established,and the design of the density meter hardware and software was completed.In the hardware part of the system,circuits such as pre-stage signal processing circuit,single-chip interface circuit,resonance circuit,and Pt100 temperature measurement circuit are designed.Using an excitation circuit to excite the piezoelectric ceramic to vibrate to make the vibrating tube vibrate according to the natural frequency,the mass changes after the liquid is introduced,and the liquid density is obtained by measuring the change of the resonant frequency,and the resonant frequency is measured by the single-chip microcomputer.The software part includes two parts: the microcontroller and the host computer.The single-chip microcomputer uses C language to control the frequency-density conversion,and the upper computer uses Lab VIEW to program the real-time online monitoring of the liquid density.Experiment with the built-up resonant tube density meter,and carry out the single-chip frequency calibration and stability experiment.Select 10 liquids with different densities for preliminary calibration of the densitometer,fit the relationship between frequency and density by the least square method,determine the K coefficient,and analyze the factors that may affect the measurement accuracy of the system.It makes the system have an accuracy of 0.5kg/m~3 within the measuring range of 700?1200kg/m~3.