Mass flow meter

Details Mass flow meter Mass flow meter

1998-05-28

2000-06-06

Noori, Max

Measuring and testing

Volume or rate of flow

Mass flow by imparting angular or transverse momentum to the...

G01F 178

Patent

active

060704748

DESCRIPTION:

BRIEF SUMMARY
The invention concerns a mass flowmeter for flowing media, which operates according to the Coriolis principle, with a preferably cylindrical, in particular circular cylindrical, housing with at least one preferably essentially straight Coriolis measuring tube located within the housing and connected at both of its ends to the housing, with a preferably cylindrical, in particular circular cylindrical, bridge located on the Coriolis measuring tube, with at least one oscillation generator acting on the Coriolis measuring tube, and with at least one sensor detecting Coriolis forces and/or Coriolis oscillations based on Coriolis forces, the bridge being located symmetrically and made symmetrically with respect to the mid-point of the Coriolis measuring tube, wherein the midpoint of the Coriolis measuring tube is defined with reference to the ends of the Coriolis measuring tube connected with the housing, and the oscillation generator and the sensor being operative between the Coriolis measuring tube and the bridge.


BACKGROUND OF THE INVENTION

Mass flowmeters for flowing media, which operate according to the Coriolis principle, are known in different embodiments (cf e.g. German Patent Specification 41 24 295 and German Offenlegungsschrift 41 43 361, and the publication cited there in each case at column 1, lines 20 to 27, German Patent Specification 42 24 397 and the publications cited there at column 1, lines 23 to 30, as well as German Offenlegungsschrift 196 01 342) and are increasingly used in practice.
In the case of mass flowmeters for flowing media which operate according to the Coriolis principle, basically one distinguishes between, on the one hand, those whose Coriolis measuring tube is made at least essentially straight, as a rule exactly straight, and, on the other hand, those whose Coriolis measuring tube is made loop-shaped. In addition, in the case of the mass flowmeters under discussion, one distinguishes between, on the one hand, those which have only one Coriolis measuring tube and, on the other hand, those which have two Coriolis measuring tubes. In the case of the embodiments with two Coriolis measuring tubes, they can be hydraulically in series or parallel to one another.
Mass flowmeters of the type in question, in the case of which the Coriolis measuring tube is, or Coriolis measuring tubes are, made straight, with respect to their mechanical construction simple and can consequently be produced at relatively low cost. In this case also it is possible to finish or polish the inner surfaces of the Coriolis measuring tube or Coriolis measuring tubes well. In addition, they have a relatively low pressure loss. In the case of mass flowmeters which operate according to the Coriolis principle, and in the case of which the Coriolis measuring tube is, or the Coriolis measuring tubes are, made straight, it can be disadvantageous that both thermally caused expansions, or thermally caused stresses, as well as forces and moments acting from outside, can lead to measurement errors and to mechanical damage, namely stress cracks.
The technical world has already dealt with the above-mentioned problems in mass flowmeters with straight Coriolis measuring tubes (cf in particular German Patent Specification 41 24 295, German Offenlegungsschrift 41 43 361, and German Patent Specification 42 24 379). In this case, these problems have largely been solved, on the one hand, by having the Coriolis measuring tube and the bridge connected to one another in a way which excludes axial relative motions, so that the axial separation of the Coriolis measuring tube/bridge connecting points represents the oscillation length of the Coriolis measuring tube and, on the other, by locating the Coriolis measuring tube within the bridge with initial tensile stress (German Patent Specification 41 24 295), and/or having the Coriolis measuring tube and the bridge consist of materials with identical or almost identical coefficients of thermal expansion (German Offenlegungsschrift 41 43 361) and/or providing a length variation sensor

REFERENCES:
patent: 5691485 (1997-11-01), Endo et al.
patent: 5796012 (1998-08-01), Gomi et al.
patent: 5814739 (1998-09-01), Van Cleve

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