Patent ID: 8676518

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 alternately drive the pair of flow tubes, and a phase difference or 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: measuring a frequency 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; transmitting a modulatable frequency signal based on the measured frequency of the first digital signal; performing frequency conversion to add or subtract the frequency of the modulatable frequency signal to or from the frequency of the first digital signal; performing frequency conversion to add or subtract the frequency of the modulatable frequency signal to or from the frequency 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; and measuring a phase difference between (i) the frequency converted first digital signal and (ii) the frequency converted second digital signal.