Capacitive electromagnetic flowmeter

Abstract

The invention relates to a capacitive electromagnetic flowmeter. A sensor of the capacitive electromagnetic flowmeter comprises a high-dielectric-constant industrial ceramic liner and a non-contact plated metal detecting sheet electrode. The sensor is provided with two opposite excitation coils serially connected to excite the inside of the sensor. The metal detecting electrode and a metal shielding electrode are connected to input and output ends of an operational preamplifier respectively to allow for equipotential shielding. A timing control circuit controls a switch of a full-bridge inverter circuit and an analog switch of a flow signal processing circuit according to logic signals of exciting current so as to control the exciting current in the coils and process the flow signals. The full-bridge inverter circuit is capable of enhancing the exciting current to increase the signal-to-noise ratio of the flow signals while inhibiting differential disturbing influence. The full-bridge inverter circuit is used with the timing control circuit to centrally control the power switch of the inverter circuit and the analog switch of the flow signal processing circuit, differential disturbance in the flow signals are removed accurately, and reliable detection on fluid flow is realized finally.

Description

technical field [0001] The invention relates to an electromagnetic flowmeter, in particular to a capacitive electromagnetic flowmeter with a higher signal-to-noise ratio. Background technique [0002] The DC power supply provides rectangular wave excitation current to the coil through the full-bridge inverter circuit to form an electromagnetic field. The fluid flowing in the measuring tube cuts the magnetic force line to generate an induced electromotive force, which is proportional to the fluid flow rate. Since the exciting current is alternating, the induced potential generated is also alternating, and its frequency is the same as that of the exciting current. A pair of electroplated sheet metal electrodes are set on the outer wall of the insulating ceramic measuring tube. The electrode plate and the fluid form a capacitance with the measuring tube wall as the medium. The induced potential is coupled to the detection electrode by using the capacitance-to-alternating signal...

AI Technical Summary

Problems solved by technology

Since the operational amplifier, field effect tube and sampling resistor are used to realize the current source function, the operating voltage of the operational amplifier, the power consumption of the field effect tube and other parameters limit the increase of the excitation voltage and excitation current. The circuit generally uses an excitation voltage of no more than 36V Voltage, the output excitation current does not exceed 0.15A, and the excitation frequency is generally below 40Hz. The excitation current of the capacitive electromagnetic flowmeter cannot be further increased. Increasing the excitation frequency and reducing the differential interference and the same direction interference restrict the improvement of the signal-to-noise ratio of the sensor.

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