Coriolis-type mass flow meter with at least one measuring tube

• US 5,736,653 A
• Filed: 06/07/1996
• Issued: 04/07/1998
• Est. Priority Date: 07/21/1995
• Status: Expired due to Fees

• Current Assignee: Endress+Hauser Flowtec AG (Endress+Hauser AG)
• Original Assignee: Endress+Hauser Flowtec AG (Endress+Hauser AG)
• Inventors: Drahm, Wolfgang, Rieder, Alfred
• Primary Examiner(s): Chilcot, Richard
• Assistant Examiner(s): THOMPSON, JEWEL VERGIE
• Application Number:
  US08/659,859
• Time in Patent Office: 669 Days
• Field of Search: 73/861.355, 73/861.356, 73/861.357
• US Class Current: 73/861.356
• CPC Class Codes: G01F 1/8409 constructional details
• CPC Class Codes: G01F 1/8413 means for influencing the flowmeter's motional or vibrational behaviour, e.g., conduit support or fixing means, or conduit attachments
• CPC Class Codes: G01F 1/8427 detectors
• CPC Class Codes: G01F 1/8431 electronic circuits
• CPC Class Codes: G01F 1/8436 signal processing
• CPC Class Codes: G01F 1/849 having straight measuring conduits

Abstract

A Coriolis-type mass flow meter is disclosed which can be installed, e.g., via flanges, in a conduit of a given diameter so as to be axially aligned with said conduit, which is traversed by a fluid to be measured. To further improve and optimize its insensitivity to vibrations originating from the conduit, this Coriolis-type mass flow meter comprises: at least one measuring tube fixed to the flanges; a support tube having its ends fixed to the respective flanges; means for exciting the measuring tube into resonance vibrations; velocity sensors positioned along the measuring tube for sensing the vibrations of the measuring tube; acceleration sensors positioned on the support tube along a line of intersection with that plane in which Coriolis forces act; and means which process signals from the velocity sensors and signals from the acceleration sensors into a mass flow signal which is substantially free from interference.

Claims

1. A Coriolis-type mass flow meter

which can be installed by means of flanges, in a conduit of a given diameter so as to be axially aligned with said conduit, through which flows a fluid to be measured,

with at least one measuring tube extending between and fixed to the flanges and traversed by the fluid,

with a support tube having its ends fixed to the respective flanges,

with means for exciting the measuring tube or measuring tubes into resonance vibrations,

with a first velocity sensor and a second velocity sensor positioned along the measuring tube or measuring tubes for measuring the vibrations of the measuring tube or measuring tubes,

with a first acceleration sensor and a second acceleration sensor positioned on the support tube along a line of intersection with that plane in which Coriolis forces act during operation of the mass flow meter, and

with means for processing signals from the velocity sensors and signals from the acceleration sensors into a mass flow signal which is substantially free from interference.

2. A mass flow meter as claimed in claim 1, comprising a single straight measuring tube.

3. A mass flow meter as claimed in claim 1, comprising a single bent measuring tube extending in one plane.

4. A mass flow meter as claimed in claim 1 wherein the means for processing the signals from the velocity sensors and the signals from the acceleration sensors into a mass flow signal comprise the following subcircuits:

a first subtracter having a subtrahend input connected to the first acceleration sensor and a minuend input connected to the second acceleration sensor;

a second subtracter having a subtrahend input connected to the first velocity sensor and a minuend input connected to the second velocity sensor;

a first summer having a first input connected to the first velocity sensor and a second input connected to the second velocity sensor;

a first multiplier having a first input connected to the output of the first subtracter and a second input to which a first calibration factor determined by calibration in the presence of vibrations acting on the mass flow meter via the conduit is applied;

a second multiplier having a first input connected to the output of the first summer and a second input to which a second calibration factor determined by calibration in the absence of vibrations acting on the mass flow sensor via the conduit is applied;

an integrator having its input connected to the output of the second subtracter;

a second summer having a first input connected to the output of the first multiplier and a second input connected to the output of the integrator;

a first inverter connected to the output of the second summer;

a first double-throw switch having a first input connected to the output of the second summer and a second input connected to the output of the first inverter;

a second inverter connected to the output of the second multiplier;

a second double-throw switch having a first input connected to the output of the second multiplier and a second input connected to the output of the second inverter;

a threshold switch having a signal input connected to the output of the second multiplier, a threshold input connected to ground, and an output connected to the control inputs of the first double-throw switch and the second double-throw switch;

a first low-pass filter connected to the output of the first double-throw switch;

a second low-pass filter connected to the output of the second double-throw switch,

said low-pass filters having an upper cutoff frequency which is approximately one order of magnitude lower than the highest frequency occurring in their input signals; and

a divider having a dividend input connected to the output of the first low-pass filter, a divisor input connected to the output of the second low-pass filter, and an output providing the mass flow signal.

5. A mass flow meter as claimed in claim 4 wherein the first subtracter and the acceleration sensors are replaced by a single acceleration sensor which measures rotation vibrations.