US 5,969,265 A · Coriolis flowmeter having its flow calibration factor independent of material density

Abstract

A single tube Coriolis flowmeter of enhanced flow sensitivity in which material flow induces Coriolis deflections in a flow tube and Coriolis-like deflections in a balance bar vibrationally coupled to the flow tube. Both the Coriolis deflections and the Coriolis-like deflections have a phase shift determined by material flow and are used co-adjuvantly to derive material flow information. The flowmeter achieves a constant flow sensitivity over a range of changes in material density by 1) varying the flow sensitivity in a first direction under control of the ratio between the drive mode vibration amplitude of the flow tube and the balance bar and 2) varying the flow sensitivity in an opposite direction under control of the ratio between the Coriolis deflection amplitude of the flow tube and the Coriolis-like deflection of the balance bar. The drive mode vibration amplitude ratio varies with changes in drive mode frequency caused by changes in material density. The amplitude ratio of the Coriolis defection and the Coriolis-like deflection changes with changes in the magnitude of the separation of the drive mode frequency and the second bending mode frequency to the balance bar density which, in turn, is caused by changes in material density.

Claims36

Dependent claims

A method of operating a Coriolis flowmeter having a flow tube and a balance bar oriented substantially parallel to said flow tube;

said method comprising the steps of:
flowing material through said flow tube;
vibrating said flow tube and said balance bar at a drive mode frequency substantially equal to the resonant frequency of said balance bar and said flow tube with material flow;
said drive mode frequency being dependent upon the density of said material flow and changing inversely with a change in density of said material flow;
inducing periodic Coriolis deflections in said vibrating flow tube in response to said material flow;
inducing Coriolis like deflections in said balance bar at said drive frequency in response to said Coriolis deflections of said flow tube;
said Coriolis like deflections define an induced mode of vibration of said balance bar having a resonant frequency sufficiently close to said frequency of said Coriolis deflections of said flow tube to increase the amplitude of said Coriolis like deflections in said balance bar;
said flowmeter being responsive to a change in density of said material flow to maintain a substantially constant flow sensitivity of said flowmeter;
said method further comprising the steps of:
generating signals representing said Coriolis deflections of said flow tube and said Coriolis like deflections of said balance bar and
deriving information regarding said material flow in response to said generation of said signals.

8 more elements

A Coriolis flowmeter having a flow tube adapted to receive a material flow, a balance bar oriented substantially parallel to said flow tube and brace bar means coupling said flow tube with said balance bar;

said Coriolis flowmeter further comprising:
drive means for vibrating said flow tube and balance bar at a drive mode frequency proximate the resonant frequency of balance bar and said flow tube with material flow;
said material flow being effective to induce periodic Coriolis deflections in said vibrating flow tube;
means including said brace bar means responsive to said Coriolis deflections of said flow tube for inducing Coriolis like deflections in said balance bar at said drive frequency;
said Coriolis like deflections having an amplitude proportional to the amplitude of said Coriolis deflections;
said Coriolis like deflections define an induced mode of vibration of said balance bar having a resonant frequency sufficiently close, but not equal, to said drive mode frequency to vary said amplitude of said Coriolis like deflections in response to a variation in said drive mode frequency;
means responsive to a change in density of said material flow to maintain a substantially constant flow sensitivity of said flowmeter;
means for generating signals representing said periodic Coriolis deflections of said flow tube and said Coriolis like deflections of said balance bar;
and
means for deriving information regarding said material flow in response to said generation of said signals.

7 more elements

Dependencies are inferred from the claim text.

Coriolis flowmeter having its flow calibration factor independent of material density

Life of this patent

Coriolis flowmeter having its flow calibration factor independent of material density

Life of this patent

Abstract

Claims36