Electromagnetic flowmeter excitation control system based on differential compensation PFM modulation

Abstract

The invention discloses an electromagnetic flowmeter excitation control system based on differential compensation PFM modulation. The electromagnetic flowmeter excitation control system is composed ofa direct-current power supply, a PFM controller, a filter circuit, a ripple compensation circuit, a differential compensation circuit, an amplitude limiting feedback circuit, an excitation sequentialcircuit, an excitation coil drive circuit and a current sampling circuit. Constant current control is realized by adopting a PFM modulation technology, system efficiency is improved, and system powerconsumption and a system temperature rise are reduced. Excitation current overshoot is suppressed by using the differential compensation circuit so that excitation current overshoot and dynamic adjustment time can be reduced and an excitation frequency can be enhanced. The ripple compensation circuit is used for reducing exciting current ripples and improving exciting current precision. The excitation sequential circuit generates two paths of complementary rectangular wave excitation signals with dead zones and controls an excitation coil driving circuit, an output end of the excitation coildriving circuit is connected with an excitation coil, and excitation current reversing is achieved. According to the excitation control system, the excitation frequency can be improved, the power consumption and the temperature rise of the excitation system are reduced, and the excitation current ripples are reduced.

Description

technical field [0001] The invention relates to the field of flow measurement, and is an excitation control system for electromagnetic flowmeters, especially an excitation control system for electromagnetic flowmeters based on differential compensation PFM modulation, which realizes high-frequency rectangular wave excitation and reduces power consumption and temperature rise of the excitation system. Reduce the excitation current ripple, suitable for high-speed measurement of slurry fluid. Background technique [0002] Electromagnetic flowmeter is an instrument for measuring the flow of conductive liquid, and its working principle is Faraday's law of electromagnetic induction. A current is passed into the excitation coil to establish a magnetic field, and the conductive liquid cuts the magnetic field line in the magnetic field, and an electromotive force is induced at both ends of the conductive liquid, and the induced electromotive force is proportional to the flow rate of ...

AI Technical Summary

Problems solved by technology

When high-frequency excitation is realized based on the principle of linear power supply, the voltage drop across the linear power supply chip or transistor is too large, resulting in high power consumption, and it is necessary to add a larger heat sink to reduce the temperature rise of the constant current control device

The patent disclosed in Chinese Patent Publication No. CN105841761A uses high-voltage and low-voltage power supply switching to realize high-frequency excitation in frequency conversion. There are complex control circuits for high-voltage and low-voltage power supply switching, and the switching time of working states is long. Constant current control uses the principle of linear power supply to cause excitation power consumption. Larger issues

For example, Chinese Patent Publication No. CN105021241 discloses an electromagnetic flowmeter excitation control system based on PWM modulation of current error control. This patent utilizes the inductive load characteristic that the current in the excitation coil cannot change suddenly, and the current of the excitation coil changes little in a small time. , through the feedback current to control the on-off of the H-bridge high-side switch to perform constant current control. When the H-bridge high-side switch device is turned on, the excitation current rises. Frequency, there are problems such as large excitation current ripple and low efficiency of PWM modulation under light load

[0008] To sum up, when the inductance value of the excitation coil and the excitation current are large, the high-frequency rectangular wave excitation has problems such as large system power consumption, low light-load efficiency, short excitation current steady-state time, and large current ripple.

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