Signal amplifying circuit for electromagnetic flow meter

Abstract

The present invention relates to a signal amplifying circuit for an electromagnetic flow meter capable of avoiding CMRR deterioration in a differential amplification circuit caused by coupling capacitance and input abnormal recovery delay, wherein a flow rate signal that is inputted between the flow rate signal input terminals (T1, T2) of a connector (CN1) is inputted into one input terminal and the other input terminal of an instrumentation amplifier U3 through resistive elements (R1, R2) and subjected to differential amplification, and the amplified output signal (V3) thereof is outputted to a sample and hold circuit (13) through a coupling capacitor (C1). Moreover, the flow rate signals that are inputted between (T1, T2) of (CN1) are buffered by buffer amplifiers (U1, U2), and the output signals (V1, V2) thereof are outputted to a fault detecting circuit (14). At this time, an interconnection (L1) that connects (T1) and the non-inverting input terminal of (U1), is guarded by a guard ring pattern (GR1), and an interconnection (L2) that connects (T2) and the non-inverting input terminal of (U2), is guarded by a guard ring pattern (GR2).

Description

technical field [0001] The invention relates to an electromagnetic flowmeter, in particular to a signal amplifying circuit technology for amplifying electromotive force obtained from a detector. Background technique [0002] In general, in an electromagnetic flowmeter that measures the flow rate of a conductive fluid, an excitation current that alternates in polarity is supplied to the excitation coil to detect the electromotive force generated between a pair of detection electrodes, and a signal amplification circuit is used to detect the electromotive force generated between a pair of detection electrodes. Differential amplification, sampling the obtained flow signal and performing signal processing, thereby measuring the flow rate of the fluid flowing in the pipe, wherein the excitation coil is arranged so that the magnetic field generation direction and the flow direction of the fluid flowing in the pipe Perpendicularly, the pair of detection electrodes are arranged in t...

AI Technical Summary

Problems solved by technology

[0006] In addition, the input impedance of the FET-input operational amplifier is very high, and the input bias current is also very small, but it is easily affected by noise, etc. generated by peripheral circuits.

In addition, if the insulation properties of the substrate deteriorate due to the influence of surrounding humidity or the adhesion of foreign matter, the input impedance will decrease.

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