Research On Crude Oil Densitometer Based On Tuning Fork Technology

One of the key problems in oil measurement is the measurement of crude oil density,which has been a difficult problem for many years.Because of the influence of many factors,such as crude oil medium,operating condition,measuring technology principle,measuring instrument and so on,some instruments for crude oil density measuring designed in our country at present can not meet the actual engineering needs and do not give full play to their functions.In order to solve the above problems,a kind of crude oil densitometer based on tuning fork technology is designed in this paper.The density is determined by measuring the resonant frequency of the tuning fork densitometer in different media.In order to assist the structural design of the tine part of the tuning fork densitometer,the simulation analysis is necessary,and the parameters of the material used in the simulation should be chosen effectively.By dynamic modal simulation,the natural frequencies and the vibration modes of the tine are obtained.By comparing the natural frequency with the measured natural frequency,the elastic modulus value and Poisson's ratio in the simulation parameters are adjusted,the simulation results are modified to ensure that the simulation model is consistent with the true fork,and the material parameters are determined.On this basis,the thickness of the beam of the tine is changed,and the influence of the beam thickness on the natural frequencies and vibration modes is simulated.According to the technical specifications and requirements of the on-line crude oil densitometer,the tuning fork densitometer system is designed,and the hardware and software design of the densitometer is completed.In the hardware part of the system,feedback sampling circuit,driving circuit,preamplifier circuit,shaping circuit,PT1000 temperature measuring circuit and display circuit are designed.The exciting drive circuit is used to excite the vibration of piezoelectric ceramics,so that the tuning fork vibrates on the natural resonant frequency.The fork tine placed in different media will change its resonant frequency,and the frequency will be detected by another piezoelectric ceramic,and the frequency will be measured by single-chip microcomputer.In the part of software design,C language software program is written to control the liquid crystal display and output of densitometer.In order to compensate the temperature of the tuning fork densitometer,the PT1000 temperature measuring circuit is designed.The linear relationship between temperature and voltage is obtained by MATLAB curve fitting,which is used to compensate for the influence of temperature on density and to ensure the measurement accuracy.In order to meet the temperature condition of tuning fork density tester and meet the demand of system temperature compensation,a temperature control system is designed to control the test temperature of density measurement.The maximum relative error of frequency measurement for tuning fork density meter is 0.07%.The density-frequency characteristics of the tuning fork densitometer are tested,the relation between density and frequency is determined by the least square curve fitting,the maximum fitting relative error is 0.03%,and the influence of test conditions on the measuring accuracy of tuning fork densitometer is determined by measuring the frequency of the tuning fork densitometer in different diameters and different depths.