초록 ▼

The mass flow rate of a fluid, for example a gas or air, for example passing through a duct or the like, is determined by placing a vibrating element in the path or stream of air flow, and measuring the damping thereof due to the air flow; the damping can easily be measured, in accordance with the i

The mass flow rate of a fluid, for example a gas or air, for example passing through a duct or the like, is determined by placing a vibrating element in the path or stream of air flow, and measuring the damping thereof due to the air flow; the damping can easily be measured, in accordance with the invention, by connecting the vibrating element in a circuit having a servo system including a controlled variable amplifier and a comparator, such as a proportional-integral (PI) controller (14) comparing the signal on the vibrating element with a reference establishing a vibrating amplitude and, in turn, controlling the amplification of the variable amplification amplifier (8) to maintain a constant amplitude of vibration, the control signal controlling the variable amplification amplifier being a measure of the damping, and hence of mass flow rate. To eliminate damping due to extraneous conditions, such as clamping of the mechanical vibrating elements, connection of electrodes and the like, an alternating current (10a) can be fed to the vibrating element, the alternating current having a frequency which is high with respect to the vibration frequency, and then being filtered out by a band-pass filter (17) tuned to the alternating current frequency, the level of the signal across the vibrating element being subtracted from the overall damping signal to thereby eliminate errors due to inherent damping of the mechanical system independent of fluid flow.

대표청구항 ▼

Mass flow meter, particularly to determine gas or air flow having a vibratory system including a mechanical vibratory element and an oscillator circuit coupled to said element and inducing vibrations therein, and comprising a controlled variable amplification amplifier connected in the oscillator ci

Mass flow meter, particularly to determine gas or air flow having a vibratory system including a mechanical vibratory element and an oscillator circuit coupled to said element and inducing vibrations therein, and comprising a controlled variable amplification amplifier connected in the oscillator circuit; a control circuit controlling the amplification of the amplifier, and hence the oscillatory energy supplied to the vibratory element to maintain constant amplitude vibrations of the vibratory element under conditions of variable damping thereof upon change in mass flow impinging on the vibratory element, means coupled to said control circuit for generating an output damping signal representative of the oscillatory energy supplied to the vibrating element to maintain the amplitude of the vibrations constant; the amplification of the amplifier, as controlled by said control circuit being representative of the rate of said fluid mass flow; and means for generating a signal representative of damping of the vibratory element independently of fluid flow, including a source of alternating current having a frequency different from the frequency of oscillation of the oscillator circuit, and connected to the oscillator circuit to apply said alternating current to the mechanical vibratory element; means for separating said flow independent damping signal from a signal generated by said oscillator circuit; and means for subtracting the flow independent damping signal from said output damping signal to provide a flow meter output signal representative of mass flow of gas or air.