Patent ID: 8374805

Claim:
A Coriolis mass flowmeter comprising: a vibrator configured to vibrate a measurement conduct line; an upstream sensor and a downstream sensor, which are placed at a certain distance in the measurement conduct line and are configured to detect vibration of the measurement conduct line; a signal computation processing section configured to compute a mass flow rate of a fluid flowing through the measurement conduct line vibrated by the vibrator based on a phase difference between a first signal of the upstream sensor and a second signal of the downstream sensor; an excitation circuit section configured to receive the first signal or the second signal and to control a drive signal of the vibrator so that the amplitude of the first signal or the second signal becomes a target value; a first effective value reception section configured to receive an effective value of the first signal; a second effective value reception section configured to receive an effective value of the second signal; a ratio computation section configured to receive the effective value of the first signal and the effective value of the second signal and to compute the ratio of both values; and an anomaly diagnosis section configured to make a comparison between the computed ratio and a certain value and to generate an alarm; wherein the excitation circuit section is configured to receive the first signal or the second signal, when said first signal and said second signal are switched periodically as inputs to said excitation circuit section, and to control the drive signal of the vibrator so that the amplitude of the received signal becomes the target value, and wherein the ratio computation section is configured to receive a hold voltage of the effective value of the first signal and a hold voltage of the effective value of the second signal in operative association with the switching, and to compute the ratio of both voltages.