Correction Of Viscosity Effect And Development Of An Intelligent Unit For Turbine Flowmeter

Turbine flowmeter is significant and is used widely. It has advantages of highaccuracy, wide measuring range, pulse output and low pressure loss. It is applied inareas of standard facilities for liquid flow, Oil trade measurement, industrial processesand scientific experiment. But the change of viscosity has a remarkable impact on theaccuracy of the turbine flowmeter, if the meter factor of turbine is not compensated,there will be a great measuring error.In order to improve the accuracy of measurement for a wide viscosity, torqueequilibrium equation of turbine was analyzed particularly. Based on a mathematicalmodel of turbine, correction of viscosity effect was put forward. In this methodkinematic viscosity and the ratio of frequency between kinematic viscosity weretreated as independent variables. The polynomials were fitted by experimental dataand the final meter factor was calculated by them.The experiment was carried on Tianjin university variable viscosity oil facilitywith DN10turbine and alterable viscosity liquid flow facility of Flow MeasurementCenter of Aviation Industry with DN10and DN50turbines. The test demonstrated:with the software correction method, the accuracy of DN10turbine flowmeterchanged from7.0%to1.2%with viscosity range between9.14cst~31.46cst, theaccuracy of DN10turbine flowmeter changed from7.8%to3.88%with viscosityrange between9.67cst~42.67cst, the accuracy of DN50turbine flowmeter changedfrom6.8%to2.37%with viscosity range between9.07cst~43.37cst.The intelligent processing unit of turbine flowmeter was researched anddeveloped. MSP430MCU was applied in this intelligent processing unit. It achievedthe functions including3.6V or24V power supply, HART communication, displaywith dot-matrix LCD, data instantaneous storage when power cut and alarm for lowpower, output4/20mA current, external watch-dog, parameters modification bybuttons, impulse processing, alarm for the limit flow, ultra-low-power in batterysupply and intrinsic safety antiknock design. This intelligent processing unit has goodcapacity of resisting disturbance in hardware and strong reliability in software. Whenthe software correction method for viscosity was embedded in this intelligentprocessing unit, it could measure the wide viscosity flow accurately, steadily and reliably.