Method and apparatus for measuring flow through a conduit by measuring the Coriolis coupling between two vibration modes

A method, comprising:

• flowing a material through a conduit while exciting a first vibration mode of the conduit at a first frequency;
• exciting a second vibration mode of the conduit at a second frequency;
• measuring the relative motion of the vibrating conduit;
• exerting a first force on the conduit such that the vibration of the second mode at the first frequency is reduced to a minimum;
• exerting a second force on the conduit such that the vibration of the first mode at the second frequency is reduced to a minimum;
• determining the flow of material through the conduit based on the magnitude of the first and second forces.

A method comprising:

• flowing a material through a conduit while exciting a first vibration mode of the conduit at a first frequency;
• exciting a second vibration mode of the conduit at a second frequency;
• measuring the relative motion of the vibrating conduit at a first point and at a second point;
• determining a first phase difference between the first point and the second point measured at the first frequency;
• determining a second phase difference between the first point and the second point measured at the second frequency;
• exerting a first force on the conduit such that the first phase difference is reduced to approximately zero;
• exerting a second force on the conduit such that the second phase difference is reduced to approximately zero;
• determining the flow of material through the conduit based on the magnitude of the first and second force.

A method comprising:

• flowing a material through a conduit;
• exciting the vibration of the conduit at the natural frequency of a vibration mode of the conduit;
• measuring the motion of the conduit;
• forcing the induced vibration of the conduit, caused by the flowing material, to approximately zero at the natural frequency of the excited vibration mode of the conduit;
• determining the flow of material through the conduit using a measure of the force.

A Coriolis flow meter, comprising:

• a conduit (502) configured to contain a material flowing through the conduit;
• at least two drivers (D1, D2) configured to excite a at least two vibration modes of the conduit;
• a sensing apparatus configured to measure the relative motion of the vibrating conduit;
• a control system configured to excite at least two vibration modes of the conduit using the at least two drivers;
• the control system configured to determine a coupling between the at least two vibration modes of the conduit;
• the control system configured to apply a force to the conduit that will reduce the coupling between the at least two vibration modes to approximately zero
• the control system configured to determine the flow of material through the conduit using a measure of the force.

A Coriolis flow meter, comprising:

• a conduit (502) configured to contain a material flowing through the conduit;
• at least two drivers (D1, D2) configured to excite a plurality of vibration modes of the conduit;
• a sensing apparatus configured to measure the relative motion of the vibrating conduit at a first point and at a second point;
• a control system configured to excite a first vibration mode of the conduit at a first frequency;
• the control system configured to excite a second vibration mode of the conduit at a second frequency;
• the control system configured to determine a first phase difference between the first point and the second point measured at the first frequency;
• the control system configured to determine a second phase difference between the first point and the second point measured at the second frequency;
• the control system configured to exert a first force on the conduit such that the first phase difference is reduced to approximately zero;
• the control system configured to exert a second force on the conduit such that the second phase difference is reduced to approximately zero;
• the control system configured to determine the flow of material through the conduit based on the magnitude of the first and second force.

A Coriolis flow meter, comprising:

• a conduit (502) configured to contain a material flowing through the conduit;
• at least two drivers (D1, D2) configured to excite at least two vibration modes of the conduit;
• a sensing apparatus configured to measure the relative motion of the vibrating conduit at a first point and at a second point;
• a control system configured to excite a first vibration mode of the at least two vibration modes of the conduit at the natural frequency of the vibration mode;
• the control system configured to force an induced vibration mode of the conduit, caused by the flowing material, to approximately zero at the natural frequency of the excited first vibration mode of the conduit;
• the control system configured to determine the flow of material through the conduit using a measure of the force.

A Coriolis flow meter comprising:

• a conduit configure to contain a material flowing through the conduit;
• a means for exciting at least two vibration modes of the conduit;
• a means for sensing the relative motion of the vibrating conduit;
• a means for determining a coupling between the at least two vibration modes of the conduit;
• a means for applying a force to the conduit that will reduce the coupling between the at least two vibration modes to approximately zero
• a means for determining the flow of material through the conduit using a measure of the force.