CN-121994315-A - Self-adaptive excitation control circuit of electromagnetic flowmeter and control method thereof

CN121994315ACN 121994315 ACN121994315 ACN 121994315ACN-121994315-A

Abstract

The invention belongs to the technical field of circuits, and particularly relates to a self-adaptive excitation control circuit of an electromagnetic flowmeter, which comprises an H-bridge driving circuit, a current sampling circuit and a voltage signal conversion circuit, wherein the power input end of the H-bridge driving circuit is electrically connected with a constant-voltage direct-current power supply, the two output ends of the H-bridge driving circuit are respectively electrically connected with two ends of an excitation coil, and the current sampling circuit is connected in series in a loop formed by the H-bridge driving circuit and the excitation coil, and is used for converting loop current into a voltage signal. The invention abandons the traditional independent constant current source module, can accurately collect and drive and control exciting current only through the combination of a constant voltage direct current power supply, an H-bridge driving circuit, a current sampling circuit and an MCU, has extremely simple circuit structure, greatly reduces the number of components, reduces the occupied area of a PCB and the material cost, and integrally carries out PWM driving and current sampling by the MCU, reduces hardware nodes, improves the integration level and the operation reliability of the system and provides a stable hardware foundation for subsequent constant current control and fault diagnosis.

Inventors

HAN LEI
HAN ZIJIAN
ZHANG RUI
ZHANG ZHI

Assignees

南京迈岳科技有限公司

Dates

Publication Date: 20260508
Application Date: 20260209

Claims (10)

1. An adaptive excitation control circuit of an electromagnetic flowmeter, comprising: The power input end of the H-bridge driving circuit is electrically connected with a constant-voltage direct-current power supply, and the two output ends of the H-bridge driving circuit are respectively and electrically connected with the two ends of the exciting coil; The current sampling circuit is connected in series in a loop formed by the H-bridge driving circuit and the exciting coil and is used for converting loop current into a voltage signal; the microcontroller is integrated with a high-precision timer, at least two PWM output channels of the high-precision timer are electrically connected with two paths of control ends of the H-bridge driving circuit, and two paths of complementary high-frequency PWM signals are output to drive the on-off of bridge arm switching tubes corresponding to the H-bridge; and the input end of the analog-to-digital converter of the microcontroller is electrically connected with the output end of the current sampling circuit and is used for collecting the voltage signal and converting the voltage signal into a current feedback value.
2. The self-adaptive excitation control circuit of an electromagnetic flowmeter according to claim 1, wherein the current sampling circuit is a precision low-temperature drift sampling resistor, the precision low-temperature drift sampling resistor is connected in series between the excitation coil and the system common ground, and voltage signals are led out from two ends of the precision low-temperature drift sampling resistor as output ends of the current sampling circuit or are connected in series with a power input end and a power input section of the H bridge circuit.
3. The adaptive excitation control circuit of an electromagnetic flowmeter of claim 2, wherein the H-bridge circuit is comprised of four switching tubes.
4. The adaptive excitation control circuit of an electromagnetic flowmeter of claim 3, further comprising a signal processing circuit having an input electrically coupled to both ends of the sampling resistor and an output electrically coupled to the ADC input of the microcontroller.
5. The adaptive excitation control circuit of an electromagnetic flowmeter of claim 4, further comprising a communication module of RS485, RS232 or HART, wherein the communication module is electrically connected to the communication interface of the microcontroller for remotely transmitting fault alarm information and receiving external control instructions.
6. A control method of an adaptive excitation control circuit of an electromagnetic flowmeter, applied to an adaptive excitation control circuit of an electromagnetic flowmeter according to any one of claims 1 to5, characterized by comprising the steps of: the self-adaptive current regulation and control comprises the steps of regulating the duty ratio difference value of two paths of complementary band dead zone high-frequency PWM signals through a microcontroller, controlling the average voltage at two ends of an exciting coil, and further self-adaptively regulating and controlling the current size and direction, wherein the current is zero when the duty ratio of the two paths of PWM is 50%, and one path of the duty ratio is higher than the other path of the duty ratio to generate forward or reverse current, so that the working magnetic field requirement of the electromagnetic flowmeter is met; Setting a target current value, collecting a current feedback value through an ADC (analog to digital converter), comparing the current feedback value with the target current value, calculating a duty ratio difference value by utilizing a PID (proportion integration differentiation) algorithm, and adjusting a PWM (pulse width modulation) duty ratio in real time to enable an actual current to adaptively track the target current value, so as to ensure the stability of an excitation magnetic field; And (3) self-adaptive fault diagnosis, namely continuously monitoring deviation characteristics of actual current and target current, and self-adaptively judging states of the exciting coil and the loop based on a long-term statistical deviation mode, so as to accurately identify hidden faults.
7. The method for controlling the self-adaptive excitation control circuit of the electromagnetic flowmeter according to claim 6, further comprising the step of adaptively calibrating and looking up a table, wherein the microcontroller outputs PWM signals with known duty ratio differences, records corresponding steady-state excitation current values, forms a duty ratio difference-current mapping table and prestores the table in a storage unit of the microcontroller, and in actual control, the initial duty ratio difference is obtained according to look-up table or interpolation calculation of target current values, and then is finely adjusted through closed-loop constant-current control, so that the response speed and accuracy of the self-adaptive control are improved.
8. The method for controlling the self-adaptive excitation control circuit of the electromagnetic flowmeter according to claim 7, wherein the two paths of PWM duty ratios meet the condition that D1=0.5+ΔD/2 and D2=0.5- ΔD/2, wherein ΔD is a duty ratio difference value, the value ranges of D1 and D2 are 0-100%, and a low-frequency rectangular wave excitation signal of the adaptive electromagnetic flowmeter is synthesized.
9. The method for controlling an adaptive excitation control circuit of an electromagnetic flowmeter of claim 8, the self-adaptive fault diagnosis method is characterized in that the judging logic of the self-adaptive fault diagnosis is as follows: The actual current is stably greater than +5% to +30% of the target current for a long time, and the excitation coil turn-to-turn short circuit is judged; The actual current is more than 130% of the target current, or the current can not be controlled in a set range even if the PID algorithm is saturated in output, and the excitation coil is judged to be in complete short circuit or serious short circuit; the actual current is stabilized below-10% of the target current for a long time, or the preset current value cannot be reached under the set duty ratio, and the poor contact, the increase of the loop resistance or the partial disconnection of the exciting coil loop are judged.
10. The control method of the self-adaptive excitation control circuit of the electromagnetic flowmeter according to claim 9, wherein in the closed loop constant current process, current deviation values of each time are stored in a circulation queue of a microcontroller, deviation mean values, variances or trends are analyzed according to preset periods to realize self-adaptive fault diagnosis, after faults are judged, alarm information is output through an RS485 communication module, fault marks are cleared when the deviations are in a normal range, and accuracy and instantaneity of fault diagnosis are ensured.

Description

Self-adaptive excitation control circuit of electromagnetic flowmeter and control method thereof Technical Field The invention belongs to the technical field of circuits, and particularly relates to a self-adaptive excitation control circuit of an electromagnetic flowmeter and a control method thereof. Background The electromagnetic flowmeter is used as core equipment for measuring the flow of a conductive medium in an industrial process, and the measurement accuracy of the electromagnetic flowmeter directly depends on the stability of a magnetic field generated by an excitation coil. In order to ensure the accuracy of the induced electromotive force when the conductive medium cuts the magnetic force lines, a constant-current excitation signal with accurate amplitude and flexible direction switching is required to be provided for the excitation coil, which is also a core technical requirement for the design of the electromagnetic flowmeter converter. The current mainstream electromagnetic flowmeter excitation scheme generally adopts a combined architecture of an independent constant current source and an H bridge driving circuit, and the architecture has a plurality of technical limitations in practical application, and is specifically as follows: The existing constant current source is mainly divided into two types of linear constant current source and switch type constant current source, which are difficult to consider in terms of performance, cost and integration level requirements: 1. The linear constant current source forms a feedback loop based on the operational amplifier and the adjusting tube, and realizes constant current through sampling resistor voltage feedback. The circuit has the advantages that the circuit structure is simple, but the adjusting tube always works in a linear region, so that the power consumption is huge, the heating is serious, the system operation efficiency is low, and the long-term stable operation of a high-power excitation scene in the electromagnetic flowmeter cannot be adapted; 2. The switch type constant current source uses a DC-DC converter as a core, and is matched with a large number of components such as a special power supply control chip, an energy storage inductor, a freewheeling diode and the like, so that the problem of low efficiency of the linear constant current source is solved, but a plurality of peripheral elements are required to be additionally arranged, so that the circuit structure is complex, the material cost is high, a large PCB area is occupied, and the miniaturization and the high-integration design of the electromagnetic flowmeter converter are seriously limited. In the combined scheme of the independent constant current source and the H bridge driving circuit, the H bridge driving circuit only bears the current direction switching function and consists of four power switching tubes, and the exciting current flow direction is changed by controlling on-off of a logic signal of a microcontroller, so that the accurate regulation and control of the current amplitude cannot be participated. More critical, this architecture lacks an efficient on-line diagnostic mechanism for the excitation coil and loop: The traditional protection mechanism can only identify dominant faults such as complete short circuit, open circuit and the like, and is difficult to detect early hidden faults such as turn-to-turn short circuit, contact resistance increase, poor contact and the like; The hidden faults can cause drift of exciting current precision and decline of magnetic field stability, not only directly affect flow measurement precision of the electromagnetic flowmeter, but also can gradually deteriorate to cause equipment shutdown, even cause interruption of industrial production flow, and remarkably reduce operation reliability and maintainability of the equipment. In addition, the excitation mode of the electromagnetic flowmeter adopts low-frequency rectangular waves, the technical requirements of no eddy current effect and no polarization effect are considered, and the cooperative control logic of the constant current source and the H bridge drive in the traditional scheme is solidified, so that the self-adaptive adjustment is difficult to carry out according to the factors such as the coil parameter discreteness, the environment temperature change and the like, the dynamic response speed of excitation current is low, the steady-state precision is low, and the anti-interference advantage of low-frequency rectangular wave excitation cannot be fully exerted. Meanwhile, the industrial scene is urgent in demand for remote operation and maintenance of equipment, the traditional scheme lacks corresponding communication interaction design, remote reporting of fault information and remote issuing of control instructions are difficult to achieve, and suitability is limited. In summary, the existing excitation scheme of the electromagnetic flowmeter has obvious defects