Mass flow rate measurement circuit and method for a mass flow/density meter

Abstract

This circuit is suitable for flow tubes ( ) the vibration frequency of which is in the order of 1 kHz. A fluid to be measured flows through the tube ( ) vibrating in operation at a frequency determined by the density of the fluid. Attached to the tube ( ) are electromagnetic vibration sensors ( ) positioned at a given distance from each other delivering sinusoidal sensor signals (x , x ). Impedance-matching devices ( ) are fed by the sensor signals. Inputs of an intermediate switch ( ) are connected to the outputs of impedance-matching devices. Additional impedance-matching device ( ) are fed by outputs of the intermediate switch. Low-pass filters ( ) are connected to the outputs of the additional impedance matching devices. The upper cutoff frequency of low-pass filter ( ) differs by about 10% to 15% from the upper cutoff frequency of low-pass filter ( ). Zero-crossing detector ( ) are fed by the outputs of the low-pass filters. The start and the stop inputs of a time-to-digital converter ( ) are connected to the outputs of the zero-crossing de-tectors, respectively. An output of a high-frequency clock generator ( ) is coupled to the clock input of the time-to-digital converter from the output signal of which and a signal (k) representative of a calibration factor, a micro-processor ( ) generates a signal (q) representative of mass flow rate.