Capacitor type electromagnetic flow meter

Abstract

The present invention discloses a capacitive electromagnetic flowmeter. The upper side and the lower side of the outer wall of a measuring tube are provided with an upper coil and a lower coil which are in series connection; the upper coil and the lower coil are connected with an exciting circuit; the left side and the right side of the outer wall of the measuring tube are provided with a left detecting electrode and a right detecting electrode; a left shielding electrode, a right shielding electrode, a left shielding ring and a right shielding ring are arranged outside the left detecting electrode and the right detecting electrode; the left detecting electrode is connected with a left preamplifier; the right detecting electrode is connected with a right preamplifier; the left preamplifier and the right preamplifier are connected with a differential amplifying circuit and a signal processing circuit. In the signal processing circuit of the invention, a rotary capacitance filter circuit has the effect close to an ideal square wave matched filter and can overcome the influence of strong noise, improve signal-to-noise ratio, detect feeble flow signals and convert the feeble flow signals to the direct current signals along flow changing, thereby achieving the measurement on fluid flow.

Description

technical field [0001] The invention relates to an electromagnetic flowmeter, in particular to a capacitive electromagnetic flowmeter. Background technique [0002] The electromagnetic flowmeter provides a rectangular wave excitation current to the coil 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 excitation current is alternating, the induced potential generated is also alternating, and its frequency is the same as that of the excitation current. A pair of comb-shaped electrode plates are set on the outer wall of the insulating measuring tube, perpendicular to the excitation coil, the electrode plates and the fluid form a capacitance with the tube wall as the medium, and the induced potential is coupled to the plate by using the coupling effect of the capacitance. The voltage difference between the two plates can be u...

AI Technical Summary

Problems solved by technology

[0003] Since the flow signal generated by the capacitive electromagnetic flowmeter sensor is very weak, generally at the μV level, and the coupling capacitance formed between the electrode and the measured fluid is very small, only tens of pF, the internal resistance of the signal becomes very large. When the flow signal is coupled, strong noise will also be coupled in, and as the conductivity of the measured fluid decreases, the noise amplitude will be larger, and the very low signal-to-noise ratio makes it possible to accurately detect the flow signal from the strong noise background increased difficulty

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