Patent ID: 6408700
Filing Date: 2002-06-25
Classification: G01F

Abstract:
A Coriolis mass flow/density meter through which a fluid to be measured flows in a direction during operation, comprising:a mass flow sensor having at least one flow tube through which the fluid to be measured can flow, said flow tube being configured to vibrate in operation at a frequency determined by its material and dimensions but varied by the density of the fluid; a first and a second vibration sensor attached to said flow tube and positioned at a given distance from each other in the direction of flow, said sensors delivering a sinusoidal first and a sinusoidal second sensor signal, respectively; a vibrator for vibrating the flow tube; and a measurement circuit including a first and a second impedance-matching device fed by the first and second sensor signal, respectively, an intermediate switch having a first and a second input coupled to an output end of the first impedance-matching device and an output end of the second impedance-matching device, respectively, a third and a fourth impedance-matching device coupled, respectively, to a first and a second output end of the intermediate switch, a first low-pass filter coupled to an output end of the third impedance matching device, said first low-pass filter having a passband, and an upper cutoff frequency, a second low-pass filter coupled to an output end of the fourth impedance matching device, said second low-pass filter having a passband, and an upper cutoff frequency, with the upper cutoff frequency of the first low-pass filter differing from the upper cutoff frequency of the second low-pass filter, and the passband covering at least the vibration frequency values occurring in operation; a first zero-crossing detector coupled to an output end of the first low-pass filter; a second zero-crossing detector coupled to an output end of the second low-pass filter; a time-to-digital converter having a start input, a stop input, and a clock input and delivering a digital signal, the start input being coupled to an output end of the first zero-crossing detector, the stop input being coupled to an output end of the second zero-crossing detector; a high-frequency clock generator having an output end coupled to the clock input of the time-to-digital converter; and a microprocessor which generates a signal representative of mass flow rate from the digital signal and a signal representative of a calibration factor and controls the switching of the intermediate switch.