CN108680210B

CN108680210B - Transient electromagnetic flow transmitter based on voltage and current differential

Info

Publication number: CN108680210B
Application number: CN201810390965.4A
Authority: CN
Inventors: 王刚; 徐科军; 邹明伟; 吴建平; 石磊; 许伟; 康一波; 汪春畅; 于新龙
Original assignee: Chongqing Chuanyi Automation Co Ltd; Hefei Polytechnic University
Current assignee: Chongqing Chuanyi Automation Co Ltd; Hefei Polytechnic University
Priority date: 2018-04-27
Filing date: 2018-04-27
Publication date: 2020-01-10
Anticipated expiration: 2038-04-27
Also published as: CN108680210A

Abstract

The invention relates to the field of flow detection, in particular to a transient electromagnetic flow transmitter based on voltage and current differentiation. The transient measurement method based on voltage and current differentiation is provided for the transient measurement process of the electromagnetic flowmeter, and the transient electromagnetic flow transmitter based on voltage and current differentiation is developed to realize the measurement method in real time. The transient measurement system comprises an excitation driving module, a signal conditioning and collecting module, a man-machine interface module, a storage module, an output module, a communication module and a software processing module. The excitation driving module excites the excitation coil to generate an induction magnetic field; the signal conditioning and collecting module synchronously samples signal voltage and exciting current by using two ADC (analog to digital converter), and sends a sampling result to the DSP; and in the DSP, a processing method based on the voltage-current differential ratio is realized in real time, and the obtained instantaneous and accumulated flow is calculated.

Description

Transient electromagnetic flow transmitter based on voltage and current differential

Technical Field

The invention relates to the field of flow detection, in particular to a transient electromagnetic flow transmitter based on voltage and current differential, and particularly relates to a measuring system which measures by utilizing the transient process of exciting current and processes in real time by adopting a voltage and current differential ratio method.

Background

An electromagnetic flowmeter is a meter for measuring the volume flow of conductive liquid based on the law of electromagnetic induction, and is widely applied to the flow measurement of various conductive liquids. At present, most of electromagnetic flow meters adopt low-frequency rectangular wave or three-value wave excitation, the steady-state excitation current is one hundred to hundreds of milliamperes, and a stable section with enough time needs to be kept, so that the output signal of a sensor obtains a stable section for a long time, and the measurement precision of the sensor is ensured. For example, a high-voltage and low-voltage power supply switching excitation control system is adopted, the high voltage is 80V, the low voltage is 17V, the steady-state current is about 180mA, the excitation is carried out by using a high-voltage source in the rising process of the excitation current, and the current is switched to a low-voltage source in the steady state, so that the excitation current quickly enters the steady state (Weiwei and the like). This results in large power consumption of the electromagnetic flowmeter, more serious heating and influences the service life of the electromagnetic flowmeter; meanwhile, the low-power-consumption realization of the electromagnetic flowmeter is not facilitated.

In order to reduce the excitation power consumption, the Liu iron force of China metrological institute and the like published a paper of 'novel low-power consumption electromagnetic flowmeter design' (2013, 24(3): 243-plus 247) in the 'Chinese metrological institute' journal. The design and implementation of low power consumption electromagnetic flow meters are published in Instrument technology and Sensors by Du Qingfu, et al, university of Shandong (2015, (3): 25-27). Both of these documents use a method of reducing the excitation voltage and intermittent excitation. Although the power consumption of the electromagnetic flowmeter can be reduced, reducing the excitation voltage affects the response speed of the electromagnetic flowmeter; the instantaneity of intermittent excitation is poor, and the measurement accuracy is reduced.

The IEEE Instrumentation & Measurement Magazine by The foreign scholars of The publications of Pulse Excitation in Electromagnetic Flowmeters (2013,16(5):47-52) was published by Michalski A et al. This document investigates the transient process of the excitation current. Compared with the steady-state measurement, the excitation current does not need to enter the steady state during the transient measurement, the excitation time is short, and a constant current source is not needed to maintain the stable section of the excitation current, so that the power consumption can be effectively reduced. However, the excitation current and the signal voltage during the transient state are both in a dynamic change process, and the differential interference is not negligible, so that the amplitude of the signal voltage is affected by the flow and the time at the same time, and the relationship between the signal voltage and the flow is difficult to determine. For the problem, in the document, the coefficients of two exponential terms of the output voltage are solved by a least square method, then the obtained coefficients are used for indirectly obtaining a result corresponding to the flow speed, and the feasibility of transient measurement is verified by processing off-line data. However, the solving process is complex, and is not easy to implement in real time.

Disclosure of Invention

In order to solve the problems, the invention adopts the following technical scheme: aiming at the problem that the signal voltage is simultaneously influenced by flow and time during transient measurement of the electromagnetic flowmeter, the dynamically changed excitation current and signal voltage are analyzed, a voltage-current differential ratio processing method is provided, the influence of time is eliminated, the relation between the voltage-current differential ratio and the flow is determined, and under the conditions that the excitation voltage is 7V, the excitation frequency is 1Hz, and the half-cycle excitation time is 8ms (at the moment, the excitation working time is equivalent to that of an intermittent excitation mode in the same time, and the signal-to-noise ratio is relatively good), voltage and current data are collected for off-line verification. Then, a transient electromagnetic flow transmitter based on voltage and current differentiation is developed by taking a DSP (digital signal processor) as a core, and a transient measurement method is realized in real time.

The transient measurement system based on voltage current differential includes: the excitation circuit comprises an excitation driving module, a signal conditioning and collecting module, a man-machine interface module, a storage module, an output module, a communication module and a software processing module, and a constant current source circuit is removed in hardware design because excitation current does not need to enter a stable state. The excitation driving module generates an excitation time sequence to control the connection and disconnection of an H bridge through an ePWM (enhanced pulse width modulation) module on the DSP chip, so as to control the excitation of the excitation coil and generate an induction magnetic field; the signal conditioning and collecting module synchronously samples exciting current and amplified and filtered signal voltage by using two 24-bit ADCs (analog-to-digital converters), and sends a sampling result to the DSP through two multi-channel buffer serial ports (Mcbsp) of the DSP. The DSP adopts digital filtering to eliminate noise interference in signal voltage, differentiates the exciting current and the filtered voltage respectively, then divides the differentiation result of the exciting current and the filtered voltage to obtain a differentiation ratio, calculates instantaneous and accumulated flow according to the instrument coefficient, and finally sends the calculated instantaneous and accumulated flow to the liquid crystal display.

The invention has the advantages that: the method is characterized in that a voltage-current differential ratio value processing method is provided for transient measurement, the linear relation between the differential ratio value and flow is determined, the transient measurement method is realized in real time based on a DSP (digital signal processor), and the developed transient measurement system reduces excitation time, remarkably reduces excitation power consumption and has good measurement accuracy and real-time performance.

Drawings

Fig. 1 shows the excitation current waveform during a transient state.

Fig. 2 shows the signal voltage at each flow rate.

Fig. 3 shows the correspondence between the output result and the flow rate in each half cycle.

FIG. 4 is a fitted curve of voltage and current differential ratio values versus flow.

FIG. 5 is a system hardware block diagram.

Fig. 6 is a main program flowchart.

Fig. 7 is an algorithm flow chart.

Detailed Description

The design idea of the invention is as follows: aiming at the problem that the signal voltage is affected by the flow and the time in the transient process, the exciting current and the signal voltage which change dynamically in the transient process are researched by analyzing a signal model in the transient process, a processing method of a voltage-current differential ratio value is provided, the influence of the time is eliminated, the linear relation between the differential ratio value and the flow is determined, and the acquired voltage and current data are utilized to carry out off-line verification. Then, a DSP chip of a TMS320F28335 model is taken as a core, and a DSP-based hardware system is developed. And writing DSP software and realizing the proposed transient measurement method in real time. In order to accurately obtain signal voltage and exciting current in a dynamic process, two 24-bit ADCs are adopted to respectively collect voltage and current signals during hardware design; in order to accurately calculate the differential ratio, the voltage and current need to be synchronously collected, and two pieces of 24-bit ADCs are configured in a synchronous sampling mode in software.

Fig. 1 shows the excitation current waveform during a transient state. It can be seen that the system stops excitation when the excitation current has not entered the steady state, and the excitation current is still in the dynamic rising process, and the current value reaches the maximum value, which is about 90 mA. During transient measurement, because the excitation time is short, the excitation current and the magnetic field generated by the induction of the excitation current do not enter a stable state, the excitation coil at the moment is treated as an inductive load, and the excitation current which dynamically rises in the transient process is

In the formula, U is excitation voltage, R is excitation loop resistance,and L is the time constant of the excitation loop and the inductance of the excitation coil. When the conductive liquid in the pipeline flows through a magnetic field generated by the induction of the exciting current, induced electromotive force is generated. Neglecting the noise influence of common mode interference, the signal voltage generated at the two ends of the sensor electrode is

In equation (2), the signal voltage is composed of two parts. One part is a voltage component, namely a flow component, generated when the conductive liquid passes through the magnetic field cutting magnetic induction line, the size of the voltage component is related to the flow, and the coefficient a corresponds to the flow speed. The other part is differential interference, the differential interference is caused by the change of the exciting current, is independent of the flow and changes along with the exciting time, and the coefficient b is independent of the flow and the exciting time.

Fig. 2 shows the signal voltage at each flow rate. Because the excitation current does not reach a steady state, the corresponding signal voltage is also in an unsteady state process and mainly comprises two parts, namely a flow component and differential interference. However, the actually acquired sensor signals introduce direct current bias and 50Hz power frequency interference. Therefore, comb-shaped band-pass filtering processing is carried out on the signal voltage to eliminate direct current bias and power frequency interference. In fig. 2, the flow rates corresponding to the signal voltage amplitudes after digital filtering from low to high are 0m in sequence³/h～30m³H is used as the reference value. The signal voltage in fig. 2 is in phase with the dynamically rising excitation current in fig. 1And (7) corresponding. It can be seen that, in the transient rising process of the exciting current, the corresponding signal voltage amplitude is not only related to the flow in the pipeline, but also changes along with the exciting time. When the flow is zero, the signal voltage is mainly differential disturbance. As time increases, the differential interference gradually decreases and changes slowly; the change trend becomes gentle while the signal voltage amplitude under other flow rates changes with time.

In the rising process of the exciting current, the flow velocity component is influenced by the induction magnetic field, and the magnitude of the flow velocity component is not only related to the flow velocity, but also changes along with the time; while the differential disturbance varies only with time, independent of the flow rate. At this time, the amplitude of the signal voltage, which is composed of the flow component and the differential disturbance, is affected by time as well as the flow velocity. Since the amplitude of the signal voltage is affected by time, it is difficult to determine the relationship between the flow rate and the signal voltage.

By analyzing the expressions of the exciting current and the signal voltage in the transient process, it can be seen that the time t is only in the exponential term e^-α*tIf the exponential term can be eliminated, then the remaining portion is only related to the flow rate. Through the analysis of the signal voltage and the exciting current in the transient process, the result of the differentiation of the signal voltage and the exciting current is found to be equal to the exponential term e^-α*tProportional, the differentiated voltage divided by the differentiated current cancels the exponential term, thereby eliminating the time effect and determining the relationship between the differentiated ratio and the flow rate. The signal voltage and the excitation current are processed as follows:

the signal voltage is subjected to differential processing to obtain

du(t)＝(a*α*I₀*e^-α*t-b*α²*I₀*e^-α*t)dt (3)

In the formula (I), the compound is shown in the specification,

differentiating the exciting current to obtain

di(t)＝α*I₀*e^-α*tdt (4)

It can be seen that both equations (3) and (4) contain only the exponential term e^-α*tProportional part. At this time, the two formulas are divided to obtain

After simplification, the product is obtained

It can be seen from equation (6) that the division of the signal voltage and the exciting current eliminates the exponential term e after differential processing^-α*tThe right side of the equation leaves a coefficient a and a disturbance component b a proportional to the flow rate. It is easy to know that a corresponding to the flow velocity only changes with the flow and is linearly related to the flow; when the flow is zero, the left interference part of the equation is-b α, which is independent of the flow rate and does not change with time, and can be treated as a zero point. Then, as can be seen from equation (6), the differential ratio of the voltage and the current is linear with the flow rate.

Fig. 3 shows the correspondence between the output result and the flow rate in each half cycle. According to the analysis of equation (6), the differential ratio of the signal voltage and the excitation current has a linear relationship with the flow rate, and increases as the flow rate becomes larger. In order to further verify the relationship between the excitation current and the filtered signal voltage, the excitation current and the filtered signal voltage are differentiated respectively, the differentiated excitation current and the filtered signal voltage are divided, amplitude demodulation is carried out on the differential ratio of the voltage and the current in each half period, and finally the demodulated average value is obtained as the output result of each half period. Each flow point in the graph corresponds to each half-cycle output result at the flow rate, and although each half-cycle output result at each flow rate fluctuates within a certain range, it is easy to see that the differential ratio of the voltage and the current has a clear linear relationship with the flow rate.

FIG. 4 is a fitted curve of voltage and current differential ratio values versus flow. And averaging the output results of each half period, and fitting by using a least square method to obtain a relation curve between the differential ratio of the voltage and the current and the flow. In the figure, the output result of the differential ratio of the voltage and the current falls on the fitting curve or is uniformly distributed on two sides of the curve, namely the differential ratio has a good linear relation with the flow. The corresponding output result when the flow is zero is not zero, and according to the analysis of the formula (6), the corresponding output result is fixed interference-b x delta alpha at the moment, is irrelevant to both the flow and the excitation time, and can be used as zero point processing.

In order to compare the excitation power consumption of the invention with that of a common electromagnetic flowmeter, a DN40 electromagnetic flowmeter is taken as an example, and the excitation power consumption in transient measurement and steady-state measurement is calculated and compared.

For a primary instrument with the caliber of 40mm, the resistance of an excitation loop of 56 omega and the inductance of an excitation coil of 127mH, the common electromagnetic flowmeter adopts an excitation control method of switching high and low voltage power supplies, the steady state excitation current is about 180mA, the excitation frequency is adjustable, and the excitation power consumption under different frequencies is basically the same. When the excitation frequency is 12.5Hz, the excitation time is 40ms per half cycle. During the period when the exciting current rises to the steady state value, the exciting power supply is a high voltage power supply, the voltage is 80V, and the known exciting loop time constant is

The excitation current at this time is

When the excitation power supply is a high-voltage power supply, the excitation current can quickly reach 180mA, and then the excitation current is switched to a low-voltage source, so that the excitation current is kept at a steady-state value. It can be known from calculation that the time for the exciting current to reach 180mA is about 0.3ms, and the exciting power consumption corresponding to the rise section is

When the excitation power supply is switched to a low-voltage power supply, the voltage is 17V, the time for the excitation current to reach a steady-state value is about 0.3ms, the half-period time is 40ms, and the power consumption corresponding to the stable section of the obtained excitation current is

W₂＝17*0.18*(0.04-0.0003)＝17*0.18*0.0397＝0.1215J

I.e. the excitation power consumption per half cycle is

W＝W₁+W₂＝0.0022+0.1215＝0.1237J

When the electromagnetic flowmeter is excited at 12.5Hz, 25 excitation half cycles are provided per second, and the power consumption of the ordinary electromagnetic flowmeter is within 1 second

W_{General purpose}＝W*25＝0.1237*25＝3.0925J

For the same primary instrument, the excitation voltage on the coil is about 7V during transient measurement, the excitation frequency is 1Hz, two excitation half cycles exist per second, the half-cycle excitation time is 8ms, the excitation current cannot enter a steady state within 8ms because the transient measurement system does not have high-low voltage switching, and the current value reaches about 90 mA.

From transient measurements of the exciting current in the coil

The excitation power consumption corresponding to each half period can be obtained as

I.e. the excitation power consumption of 2 half cycles in 1 second at the time of transient measurement is

W_{Instant heating device}＝W₃*2＝0.0051*2＝0.0102J

By comparison, the excitation power consumption of the transient measurement system per second is about 1/300 of the common electromagnetic flowmeter, which shows that the transient measurement reduces the excitation time and greatly reduces the excitation power consumption.

FIG. 5 is a system hardware block diagram. The hardware mainly comprises an excitation driving module, a signal conditioning and collecting module, a man-machine interface module, a storage module, an output module and a communication module.

In the excitation driving module, an excitation time sequence is generated through an on-chip peripheral ePWM of the DSP to control the on-off of an H bridge in an excitation control circuit, so that the excitation of the excitation coil is controlled. Compared with the common electromagnetic flowmeter, the system of the invention eliminates a constant current source circuit in the hardware design and also reduces the excitation power consumption because the excitation current does not need to enter a steady state during transient measurement.

The signal conditioning and collecting module comprises a sensor signal processing and collecting part and an exciting current signal collecting part. In the sensor signal conditioning and collecting part, a sensor signal is firstly amplified through a differential circuit, then the signal reference is regulated through a bias regulating circuit, then high-frequency noise is filtered through a filter circuit, and finally the filtered voltage is converted into digital quantity through an analog-to-digital converter ADC1 and is sent to a DSP for calculation. Because the actual output of the sensor contains the direct current offset, and the offset is a variable quantity, the offset is adjusted by using a DAC (digital-to-analog converter) to ensure that the ADC can sample normally. In the exciting current collecting part, exciting current is firstly measured by using a current detecting circuit, and then is converted into digital quantity through an analog-to-digital converter ADC2 to be transmitted to a DSP.

The man-machine interface module comprises a keyboard and liquid crystal. In the working process of the system, the DSP monitors whether a key is pressed down in an inquiry mode, and relevant parameters are modified and set through operating the key; the DSP utilizes a GPIO (general purpose input/output) port to simulate an SPI (serial peripheral interface) to transmit data to the liquid crystal in series, and real-time display of flow and related information is realized.

In the memory module, an external interface XINTF module external SRAM (static random access memory) is used for storing longer program codes and data. And storing key instrument parameters and the accumulated flow during the last power failure by using a ferroelectric memory so as to ensure that the instrument can work normally when being powered on again.

In the output module, 4-20 mA current is output through the GPIO port. In the communication module, the RS485 is used for communicating with an upper computer to realize data uploading and parameter setting.

Fig. 6 is a main program flowchart. The main program is a total scheduling program of the whole transient measurement system, and the subprograms of all modules are called to realize all functions required by the instrument. The main program is a dead loop, and the system starts to work as soon as being powered on and enters a loop of continuous calculation and processing. The software working flow is as follows: initializing the system immediately after the system is powered on; after initialization is completed, two ADCs are configured to start synchronous sampling; then, starting excitation interruption, starting excitation to work, and exciting the excitation coil; after the half-cycle sampling is finished, judging whether the acquired signal voltage exceeds the limit; then calling an algorithm module, processing the acquired signal voltage and the acquired excitation current by using a transient measurement method, and calculating to obtain a differential ratio of the voltage to the current; then, the instantaneous flow and the accumulated flow are calculated according to the set meter coefficient, and the liquid crystal display is refreshed in real time.

The system of the invention has the working process that: the excitation driving module generates an excitation time sequence through an ePWM (enhanced pulse width modulation) on-chip and an ePWM (enhanced pulse width modulation) on-chip of the DSP (digital signal processor) to control the on-off of an H bridge in the excitation circuit, so as to control the excitation of the excitation coil and generate an induction magnetic field. When the conductive liquid in the pipeline flows through a magnetic field generated by the induction of the exciting current in the coil, signal voltage is generated on the electrode of the sensor. After differential amplification, offset adjustment and filtering, the signal voltage and the exciting current measured by the current detection circuit are synchronously sampled by two analog-to-digital converters ADC1 and ADC2 of the same type, and after the signal voltage is sampled by the two analog-to-digital converters, the voltage and the current are converted into digital quantity from analog quantity; then, the signals are sent into the DSP through two multi-channel buffer serial ports (McbspA and McbspB) of the DSP. In the DSP, after the half-cycle sampling is finished, whether the signal voltage exceeds the limit is judged. And if the threshold is exceeded, adjusting the bias through a digital-to-analog converter (DAC) and a bias adjusting circuit. Then, a comb-shaped band-pass filter is adopted to carry out digital filtering on the signal voltage, then the exciting current and the filtered voltage are respectively subjected to differential processing, and the differential ratio of the exciting current and the filtered voltage is calculated; and finally, calculating to obtain instantaneous flow and accumulated flow, and refreshing and displaying the flow and related information in real time through a liquid crystal.

Fig. 7 is an algorithm flow chart. The algorithm program is realized in real time by a voltage-current differential ratio method, and the basic flow is as follows: firstly, a comb-shaped band-pass filter is utilized to carry out digital filtering on signal voltage obtained by sampling; then, carrying out differential processing on the filtered signal voltage and carrying out differential processing on the exciting current; then, dividing the voltage differential by the current differential, and carrying out half-cycle demodulation on the differential ratio; and finally, solving the average value of the adjustment result as an output result to participate in the flow calculation. And after the algorithm program is executed, returning to the main cycle again, and calling the liquid crystal display program to send the calculated flow to the liquid crystal display at the moment.

Table 1 shows the water flow calibration results. The developed electromagnetic flow transmitter is matched with the developed clamping type sensor with the caliber of 40mm, and a water flow calibration experiment is carried out on the water flow calibration device. In the experiment, a volumetric method is adopted for calibration, namely, the flow result measured by the electromagnetic flowmeter is compared with the volume in the measuring cylinder, and the measurement accuracy of the electromagnetic flowmeter is verified.

TABLE 1 Water flow calibration results

The experimental data are shown in Table 1, and a total of 4 flow points were determined, wherein the maximum flow rate was 5m/s and the minimum flow rate was 0.5 m/s. Experimental results show that the measurement accuracy of the transient electromagnetic flow transmitter based on voltage and current differentiation meets the requirement of 0.5%. Experiment verification shows that the system for measuring by using the transient process of the exciting current can meet the accuracy requirement of the common electromagnetic flowmeter by adopting a voltage and current differential ratio processing method.

Claims

1. A transient electromagnetic flow transmitter based on voltage and current differential is disclosed, aiming at the problem that signal voltage is affected by flow and time simultaneously during transient measurement of an electromagnetic flowmeter, dynamically changing exciting current and signal voltage are analyzed, a processing method of voltage and current differential ratio is provided, the influence of time is eliminated, the relation between the voltage and current differential ratio and the flow is determined, and voltage and current data are collected for off-line verification; a transient electromagnetic flow transmitter based on voltage and current differentiation is developed by taking a DSP as a core, and a transient measurement method is realized in real time; transient measurement system based on voltage current differential includes excitation drive module, signal conditioning collection module, man-machine interface module, storage module, output module, communication module and software processing module, its characterized in that: the excitation driving module generates an excitation time sequence through an ePWM (electronic pulse width modulation) on a chip of the DSP (digital signal processor) to control the on-off of the H bridge, so as to control the excitation of the coil and generate an induction magnetic field; when the conductive liquid in the pipeline flows through a magnetic field generated by the induction of exciting current in the coil, signal voltage is generated on the electrode of the sensor; after differential amplification, offset adjustment and filtering, the signal voltage and the exciting current measured by the current detection circuit are synchronously sampled by two analog-to-digital converters ADC1 and ADC2 of the same type, and after the signal voltage is sampled by the two analog-to-digital converters, the voltage and the current are converted into digital quantity from analog quantity; then, the data is sent into the DSP through two multi-channel buffer serial ports of the DSP; in the DSP, judging whether the signal voltage exceeds the limit after the half-cycle sampling is finished; if the digital-to-analog converter exceeds the limit, carrying out offset adjustment through a digital-to-analog converter (DAC) and an offset adjusting circuit; then, a comb-shaped band-pass filter is adopted to carry out digital filtering on the signal voltage, then the exciting current and the filtered voltage are respectively subjected to differential processing, and the differential ratio of the exciting current and the filtered voltage is calculated; and finally, calculating to obtain instantaneous flow and accumulated flow, and refreshing and displaying the flow and related information in real time through a liquid crystal.

2. The transient electromagnetic flow transmitter based on voltage current differentiation of claim 1 wherein: aiming at the problem that the signal voltage is influenced by the flow and the time in the transient process, the exciting current and the signal voltage which are dynamically changed in the transient process are researched, and a processing method of a voltage-current differential ratio is provided, namely, through the analysis of the signal voltage and the exciting current in the transient process, the differential results of the signal voltage and the exciting current are found to be equal to an exponential term e^-α*tProportional, the voltage and current are differentiated and then divided to eliminate exponential terms, so that the influence of time is eliminated, and a linear relation between the differential ratio and the flow is determined; performing off-line verification by using the acquired voltage and current data; secondly, developing a DSP-based hardware system by taking a TMS320F28335 model DSP chip as a core; and writing DSP software and realizing the proposed measuring method in real time.

3. The transient electromagnetic flow transmitter based on voltage current differentiation of claim 1 wherein: the system stops excitation when the excitation current does not enter a steady state, so that the excitation time is reduced, and the excitation power consumption is greatly reduced; compared with the common electromagnetic flowmeter, the system of the invention eliminates a constant current source circuit in the hardware design and also reduces the excitation power consumption because the excitation current does not need to enter a steady state during transient measurement.

4. The transient electromagnetic flow transmitter based on voltage current differentiation of claim 1 wherein: the voltage-current differential ratio method is realized in real time in an algorithm program; firstly, a comb-shaped band-pass filter is utilized to carry out digital filtering on signal voltage obtained by sampling; then, carrying out differential processing on the filtered signal voltage and carrying out differential processing on the exciting current; then, dividing the voltage differential by the current differential, and demodulating the differential ratio half cycle; and finally, solving the average value of the adjustment result as an output result to participate in the flow calculation.

5. The transient electromagnetic flow transmitter based on voltage current differentiation of claim 1 wherein: in order to accurately obtain signal voltage and exciting current in a dynamic process, two 24-bit ADCs are adopted to respectively collect voltage and current signals during hardware design; to accurately calculate the voltage and current differentiated ratio, two-slice 24-bit ADCs were configured in software in a synchronous sampling mode.