Research On A Thermal Mass Flowmeter Based On Single Probe And New Measuring System

Gas flowmeter is used to measure the gas flow of some pipes, and its typicalapplication is the flow survey of compressed air system. It is widely used in theindustries such as spaceflight, energy sources, medicine, foodstuff, motorcar industryand natural gas transportation. As the thermal gas mass flowmeter has the advantagessuch as low loss of pressure, large measure range, high precision, it is widely used.However, the home market of that kind of flowmeter has always been monopolizedby foreign products. The reason is that the home enterprises can’t master thetechnology and the related fabrication processes, therefore, the products don’t havelong-time stability and good precision.In this paper, a new single-probe flowmeter has been development through theresearching on the double-probe flowmeter. Great changes have been made in sensorpart and measuring system, and some test have been done for the new flowmeterswhich have been developed. Firstly, the sensor part of the flowmeter has beenimproved, including the structural design of the shell of the single-probe flowmeter,the development of the package processes of the heat sensitive sensor. This kind offlowmeter uses only one probe, and makes the velocity probe and sensor head aswhole to process, which can increase the airproof of the sensor part. What’s more, asthe velocity sensor always located in the middle of the pipes, so the installation of theflowmeter becomes more convenient. Some test has been done for the single-probesamples which have been development. Use existing measuring system to test thesensor samples’ long-time stability, response speed and the influence from ambience.Then the measuring circuit of the flowmeter also has been improved. The newflowmeter used PID control circuit instead of bridge circuit, it adjusts the PWMwave’s duty ratio according to PID algorithm, so the voltage of velocity sensor willbe changed, then it can control the temperature difference of the sensors, andaccomplish the measurement of the gas flow. Some test has been done by making useof PID control circuit which has been developed. The testing objects including long-time stability, response speed, etc. The testing result showed that compared to bridgecircuit, PID control circuit can make the temperature difference of the two sensorsmore closed to idea value, and the power that velocity sensor consumes jumps muchslower when stable. PID control circuit also has better long-time stability and it canincrease the ratio of finished products.According to the test, the new flowmeter has great advantages compared tocustom flowmeter. It satisfy the demand of high precision thermal gas massflowmeter, and it is used for the research of related projects.