Patent ID: 8725433

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 alternately driven by causing a vibrator to be actuated by a driving device and vibrate the at least one flow tube or the pair of flow tubes, and at least one of 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 by velocity sensors or acceleration sensors which are a pair of vibration detection sensors provided on a left-hand side and a right-hand side of the at least one flow tube or the pair of flow tubes, the Coriolis force being proportional to and thereby being used to obtain at least one of a mass flow rate and the vibration frequency used to obtain a density of a fluid to be measured, the signal processing method comprising: converting, using an A/D converter, an analog signal, which is output from each of the pair of vibration detection sensors, to a digital vibration frequency signal; measuring the vibration frequency of the at least one flow tube or the pair of flow tubes; generating a control signal for controlling a frequency of the digital vibration frequency signal obtained through the conversion of the analog signal to be 1/N of the frequency thereof, based on the digital vibration frequency signal output from one of the pair of vibration detection sensors and measured in the measuring of the vibration frequency; and subjecting the digital vibration frequency signal obtained through the conversion of the analog signal to orthogonal conversion by using the control signal generated, to thereby obtain a frequency signal that has a frequency thereof set to 1/N of the frequency of the digital vibration frequency signal obtained through the conversion of the analog signal, wherein a phase difference between detection signals from the pair of vibration detection sensors is detected by using the frequency signal obtained through the orthogonal conversion, which has the frequency thereof set to 1/N of the frequency of the digital vibration frequency signal.