Transient Measurement Principle Based Electromagnetic Flow Measurement Method And Its Implementation

The electromagnetic flowmeter(EMF)is a flow measuring instrument based on Faraday's law of electromagnetic induction.It is widely used to measure conductive liquids due to its advantages of no barriers in the measurement pipeline and high reliability.At present,the EMF mostly uses the steady-state measurement,and measure the flow rate in the back part of stable-state section of excitation current.Although this ensures the measurement accuracy,the EMF has large power consumption,severe heat generation;at the same time,it is inconvenient to achieve low power consumption and portable.In order to reduce the excitation power consumption,the transient measurement is studied.The transient measurement uses the transient section of the excitation current to measure the flow rate.The excitation current has no stable-state section,which greatly reduces the excitation time and thus reduces the excitation power consumption.However,the excitation current and signal voltage during transient measurement are in a transient process that changes with time.The signal voltage is not only related to the flow rate in the pipeline,but also affected by time,which makes it difficult to determine the relationship between the signal voltage and the flow rate in the pipeline.To tackle these problems,by studying the signal model of the transient state,the excitation current and signal voltage of transient process are analyzed,and three measurement methods of the voltage-current ratio,voltage-current differential and differential interference compensation are proposed;Among them,the voltage-current ratio method divides the voltage by the current and takes the same phase point to eliminate the influence of time,and determines the linear relationship between the voltage-current ratio and the flow rate;The voltage-current differential method divides the differentiated voltage by the differentiated current to eliminate the influence of time,and determines the linear relationship between the voltage-current differential ratio and the flow rate;The differential interference compensation method compensates the voltage by calculating the differential interference in real time,divides the compensated voltage by the current to eliminate the influence of time,and determines the linear relationship between the processing result and the flow rate.In order to verify the three transient measurement methods,the DSP-based electromagnetic flow transmitter hardware system is developed to acquire the transient excitation current and signal voltage,and the programs of these three methods are written in Matlab to process the data offline.The offline processing results show that there is a good linear relationship between the processing results of the three methods and the flow rate.The DSP-based electromagnetic flow transmitter software is written,the transient measurement methods is realized in real time,and the experiment of water flow calibration and power consumption test is performed.The experimental results show that the measurement accuracy of the electromagnetic flowmeter using the transient measurement method reaches 0.5%,which is the same as the measurement accuracy of the ordinary electromagnetic flowmeter.The power consumption comparison shows that the excitation system power consumption of the electromagnetic flowmeter based on the transient measurement principle is 1/1200 of that of the ordinary electromagnetic flowmeter,which greatly reduces the power consumption.