Patent ID: 8676517

Claim:
A signal processing method for a Coriolis flowmeter in which at least one flow tube or a pair of flow tubes which is included in a measurement flow tube is operated by a driving device using a vibrator to drive the at least one flow tube or to alternatively the pair of flow tubes, and a phase difference and a vibration frequency proportional to a Coriolis force acting on the at least one flow tube or the pair of flow tubes is detected using a pair of vibration detection sensors when the at least one flow tube or the pair of flow tubes is vibrated, to thereby obtain a mass flow rate or density of a fluid to be measured, the signal processing method comprising: performing frequency conversion of a first digital signal obtained by converting a first input signal from one of the pair of vibration detection sensors into the first digital signal, the frequency conversion performed on the first digital signal modulating the frequency of the first digital signal so that the frequency of the first digital signal after the frequency conversion is 1/Nth of the frequency of the first digital signal before the frequency conversion, where N is an integer greater than 1; performing frequency conversion of a second digital signal obtained by converting a second input signal from the other one of the pair of vibration detection sensors into the second digital signal, the frequency conversion performed on the second digital signal modulating the frequency of the second digital signal so that the frequency of the second digital signal after the frequency conversion is 1/Nth of the frequency of the second digital signal before the frequency conversion; and measuring a phase difference between (i) the frequency converted first digital signal and (ii) the frequency converted second digital signal.