Digital flowmeter

摘要

A control and measurement system for a coriolis flowmeter having a flowtube, a driver adapted to vibrate the flowtube, and a pair of sensors adapted to generate signals indicative of movement of the flowtube when it is being vibrated by the driver, wherein the sensors are positioned relative to one another so the signals from the sensors are indicative of a mass flow rate of fluid through the flowtube. A digital drive signal generator is adapted to generate a variable digital drive signal for controlling operation of the driver. The digital drive signal generator can be adapted to cause the driver to resist motion of the flowtube during a first time period and amplify motion of the flowtube during a second time period. The digital drive signal generator can also be adapted to initiate motion of the flowtube by sending one or more square wave signals to the driver.

主权项

1. A Coriolis flowmeter comprising:
a pair of conduits configured to convey a fluid through the flowmeter, each conduit defining a fluid passage having at least one curve; a driver configured to oscillate the conduits in substantially opposite phase to one another; a first sensor configured to generate a first signal indicative of relative movement of the pair of conduits when they are oscillated by the driver, the first sensor being positioned at a first location; a second sensor configured to generate a second signal indicative of relative movement of the pair of conduits when they are oscillated by the driver, the second sensor being positioned at a second location, the first and second sensors being positioned so a phase difference between the first and second signals is related to a mass flow rate of the fluid through the flowmeter; a digital signal processor configured to detect the phase difference and determine the mass flow rate of the fluid using the detected phase difference and output a signal indicative of the determined mass flow rate; and a digital drive signal generator configured to:
combine the first and second signals to produce a combined sensor signal;produce a variable digital drive signal using the combined sensor signal, the variable digital drive signal having a frequency that is substantially at a resonant frequency of the conduits as determined using at least one of the first and second signals;determine a time delay associated with one or more components connected between the sensors and the driver;adjust a phase of the variable digital drive signal to compensate for the determined time delay; andselectively adjust the drive signal to cause the driver to resist motion of the pair of conduits when an amplitude of at least one of the sensor signals exceeds a set point.