WO2009050133A1

WO2009050133A1 - Mass flow meter and method for producing a reinforcement frame for a mass flow meter

Info

Publication number: WO2009050133A1
Application number: PCT/EP2008/063692
Authority: WO
Inventors: Morten Clausen; Steen Skytte Jensen
Original assignee: Siemens Aktiengesellschaft
Priority date: 2007-10-11
Filing date: 2008-10-11
Publication date: 2009-04-23
Also published as: DE102007048881A1

Abstract

The invention relates to a mass flow meter for flowing media operating according to the Coriolis principle, and comprising a pair of measuring tubes (2, 3) extending substantially parallel to each other. The measuring tubes (2, 3) are mechanically coupled to each other at a starting segment (5) and an end segment (11) by a reinforcement frame (4, 40) at least partially filled with a metal foam in order to improve the stiffness thereof. The reinforcement frame (4, 40) has recesses (21, 22) for the starting and end segments to penetrate, can be produced at a particularly low cost, and is characterized by high rigidity and low weight.

Description

description

Mass flow meter and method for producing a stiffening frame for a mass flow meter

The invention relates to a mass flowmeter for flowing media, which operates on the Coriolis principle, according to the preamble of claim 1 and a method for producing a stiffening frame for such a mass flow meter according to the preamble of claim 3.

Such a mass flow meter for flowing media, which operates on the Coriolis principle, is known for example from US 6,308,580 Bl. It is designed with two Coriolis measuring tubes, which are fluidically parallel to each other. These are one-piece, U-shaped measuring tubes, each having a straight inlet section, a straight outlet section, an inlet manifold connected to the inlet section, an outlet manifold connected to the outlet section, a first straight leg of a U connected to the inlet manifold -shaped center portion, a second connected to the outlet manifold, straight leg of the U-shaped central portion, a first, connected to the first leg manifold of the U-shaped center portion, a second, connected to the second leg manifold of the U-shaped center portion and a straight yoke portion between the first and the second manifold. The inlet sections are in an inlet manifold, also called inlet splitter, and the outlet sections in an outlet distributor piece, also called outlet splitter, fixed and thus mechanically coupled to each other. Einlaufverteilerstück and Auflaufverteilerstück form two opposite end cover of a substantially cuboid stiffening frame, from which the U-shaped middle portions of the two measuring tubes protrude laterally. In the middle of the straight yoke sections is an exciter arrangement, which the two measuring tubes, which thus pairs are made identical, so that it vibrates to vibrate against each other, that is, that the vibrations of the two measuring tubes are 180 ° out of phase with each other. The position of the center of mass of the system formed by the two measuring tubes remains substantially constant and occurring forces are largely compensated. This has as a positive consequence that the oscillating system is hardly effective to the outside as such. In the piping system in which such a mass flow meter is installed, vibrations of the measuring tubes of the mass flow meter are transmitted only to a small extent and on the other hand affect vibrations of the piping system with a suitable design of the mass flow meter hardly the measurement result. In front of and behind the exciter arrangement, vibration detectors are mounted as receivers, between whose output signals a phase difference can be evaluated as a measuring signal in the case of a flow. This is caused by the prevailing at a flow Coriolis forces. In practice, such an arrangement often provides a non-zero phase difference even when there is no flow in the measuring tube. This may be due to clamping forces, different temperature loads, irregularities in the pipe material, phase errors in the detectors or the associated circuits of an evaluation device and much more. To improve the accuracy of measurement are in the transition region of the inlet section on the inlet manifold, in the transition region of the inlet manifold on the first leg of the U-shaped center section, in the transition region of the second leg on the outlet manifold and in the transition region of the outlet manifold on the outlet portion each node plates attached, which the relative Position the measuring tubes to fix each other. Clamping forces and vibrations of the piping system in which the mass flowmeter is installed should be kept away from the two measuring tubes by the stiffening frame. In order to achieve a high rigidity of the stiffening frame, it has to be provided with comparatively thick side walls, which, when using expensive materials, contributes to For example, stainless steel, high production costs and high weight of the mass flowmeter leads.

From DE 101 27 716 Al a process for the production of metal / metal foam composite components is known, which are characterized by a lightweight construction, high rigidity and good damping properties. Various methods for producing reduced-weight profiles with increased rigidity are described, in which cavities are filled with metal foam.

From DE 102 05 070 Al also metal / metal foam composite parts for improving the vibration damping over conventional components are known.

From US Pat. No. 6,533,065 B2 it is known to provide metal foam walls in a pipe section, which is connected upstream of the measuring tube of an ultrasonic flowmeter. The metal foam walls serve there for damping of the ultrasound introduced into the measuring tube via the liquid.

The invention is based on the object, a mass flow meter for flowing media, which operates on the Coriolis principle, with a pair of substantially parallel to each other extending measuring tubes, wherein the measuring tubes in an initial section and in an end portion mechanically at least by a stiffening frame coupled together, and to provide a method for producing a stiffening frame for a mass flow meter, which are characterized by good measuring properties, low weight and low production costs.

To solve this problem, the new mass flowmeter of the type mentioned in the characterizing part of claim 1 features. In claim 2, an advantageous development, described in claim 3, a manufacturing method. The invention has the advantage that the mechanical coupling of the measuring tubes in their beginning and end sections by the stiffening frame with the same weight is much stiffer than was the case in the previous use of a trained as a hollow body stiffening frame. On the other hand, the stiffness of a conventional stiffening frame can now be achieved with significantly lower weight and thus lower material costs and costs. In addition, vibrations are damped by the metal foam, so that on the one hand vibrations of the measuring tubes are coupled to a lesser extent in the piping system and the other vibrations of the piping system less in the measuring tubes. An improved bending and torsional stiffness of the stiffening frame ensures that practically no couplings of mechanical stresses take place in the center section which is held free-swinging between the start and end sections. Mechanical stresses caused, for example, by clamping forces or changes in the pipeline into which the mass flowmeter is installed at the measuring location are to a considerable extent absorbed by the stiffening frame due to its stable design. The geometry of the center section, which is essential for the measurement properties of the mass flow meter, on the other hand remains advantageously unaffected. Therefore, changes at the installation site hardly affect a zero offset. The dimensions of the stiffening frame required to achieve these properties can be determined by finite element method calculations or by experimental experimentation.

Advantageously, a particularly compact construction is achieved with good measurement accuracy of the mass flow meter, when the two measuring tubes are bent in the central portion substantially U-shaped, beginning and end portion of each measuring tube has a substantially straight inlet and outlet section whose tube axes in a line lie, and have an inlet or outlet manifold for transfer from the inlet section to the first, substantially straight Leg of the U-shaped central portion or for the transmission of the second, substantially straight leg of the U-shaped central portion of the outlet portion and when the two measuring tubes are connected at their inlet portions and at their outlet portions with the stiffening frame.

The stiffening frame can be produced particularly cost-effectively, if initially a flat cylindrical stainless steel plate of the required thickness, a substantially cylindrical tube is bent, which is closed at its open ends with caps and then filled with metal foam. Thereafter, recesses for the passage of the measuring tubes can be mounted in the tube walls and the metal foam. After inserting the measuring tubes, inlet and outlet splitters are placed in place of the caps and welded to the ends of the stainless steel tube.

Alternatively, the stiffening frame can be made, for example, from a seamlessly shaped and filled with metal foam tube or from a double-walled tube whose wall space is filled with metal foam.

With reference to the drawings, in which an embodiment of the invention is shown, the invention and refinements and advantages are explained in more detail below.

Show it:

Figure 1 is a schematic representation of a mass flow meter and

Figure 2 is a sectional view for explaining the production of a stiffening frame.

A mass flow meter 1 according to FIG. 1 operates on the Coriolis principle. A first measuring tube 2 and second measuring tube 3 are arranged substantially parallel to one another. They are usually made in one piece by bending. manufactures. The course of the measuring tubes 2 and 3 is subdivided into the following sections: an initial section, which consists of a inlet section concealed in the figure by a stiffening frame 4 and therefore not visible, and an inlet bend 5, a middle section consisting of a first straight leg 6, an elbow 7, a straight yoke 8, a manifold 9 and a second straight leg 10, and an end portion consisting of an outlet manifold 11 and a substantially straight, in turn hidden in the figure by the stiffening frame 4 outlet portion. A flowable medium flows according to an arrow 13 in the mass flow meter 1 and thus in the two located behind a not visible in the figure inlet splitter inlet sections of the measuring tubes 2 and 3 and corresponding to an arrow 15 from the outlet sections and behind it, also in the figure invisible casserole splitter off again. Flanges 14 and 16, which are fixedly connected to the inlet splitter and the outlet splitter, serve for fastening the mass flowmeter 1 in a pipeline, not shown in the figure. The two measuring tubes 2 and 3 are mirror-inverted with respect to a perpendicular to the measuring tube axis at the apex of the substantially U-shaped central portion extending plane. Pairwise mirror images of each other arranged node plates 17, 18, 19 and 20 serve to improve the measurement properties by fixing the two measuring tubes 2 and 3 at the respective location of their attachment to each other. Their task is to separate the natural natural vibration of the measuring tubes 2 and 3, which adjusts itself when the fluid is at rest, from the Coriolis forces based vibration with flowing fluid and to reduce the transmission of vibrations between the piping system and measuring tubes. A further reduction of the influences of the piping system on the measurement properties of the mass flow meter 1 is achieved by the stiffening frame 4, with which the measuring tubes 2 and 3 are mechanically fixed in their initial section and end section. By the stiffening frame 4, the geometry of the measuring tubes 2 and 3 kept largely constant, so that even changes in the piping system, in which the mass flowmeter 1 is installed, for example, due to temperature fluctuations, possibly lead to a low zero shift. The stiffening frame 4 is formed of a relatively thin jacket sheet made of stainless steel, which is filled with a foam of metal, such as aluminum. In the stiffening frame 4 recesses 21 and 22 for receiving the measuring tubes 2 and 3 are provided. An energizing arrangement 23 shown symbolically in FIG. 1, which can consist, for example, of a magnet coil attached to the measuring tube 2 and a magnet immersed in the measuring tube 3, which immerses in the magnet coil, serves to generate mutually opposite oscillations of the two measuring tubes 2 and 3 whose frequency the natural frequency of the substantially U-shaped center portion of the measuring tubes 2 and 3 corresponds. A pickup 24 and a pickup 25, the structure of which may correspond to that of the exciter assembly 23, serve to detect the Coriolis forces and / or based on the Coriolis forces oscillations of the measuring tubes 2 and 3, which arise due to the mass of the medium flowing through. The phase shift between the measurement signals, which are generated by the two transducers 24 and 25, evaluates an evaluation device 26 for calculating a measured value for the flow. The evaluation device 26 simultaneously serves to control the exciter arrangement 23.

Deviating from the exemplary embodiment shown, the measuring tubes 2 and 3 can of course have other geometries, for example a V-shaped or Ω-shaped middle section, or a different number and arrangement of excitation arrangements and transducers can be selected.

The position of the zero point of the mass flow device 1 is determined during commissioning by calibration and stored in a memory 27 as calibration data. Based on the stored calibration data, the evaluation device determines tion 26 in response to the measurement signals the measured value, which is output on a display 28 or transmitted via a not shown in the figure fieldbus to a higher-level control station. From time to time, a recalibration makes sense, in which new calibration data for eliminating a measurement error determined and stored in the memory 27 for consideration in future measurements. Since the new mass flowmeter 1 is characterized by a particularly low zero offset, the time intervals between calibration operations can be extended so that the effort required to operate the mass flowmeter 1 is reduced due to the invention.

A manufacturing method of a stiffening frame 40, which is associated with particularly little effort, will be explained below by way of example with reference to FIG. For a clearer illustration, FIG. 2 is not true to scale. From a commercially available stainless steel plate of the required thickness, a rectangular sheet metal is punched out and bent into a tube 41, which is comparatively thin-walled and welded to the running parallel to the tube axis abutting edges. On the open ends of the tube 41, two caps 42 and 43 are placed, wherein the cap 43 has a recess 44. Metal foam 45 is then injected through the recess 44 into the cavity of the tube 41 and in this way the tube 41 is filled with foam. After curing of the metal foam, the caps 42 and 43 are removed, recesses for the two measuring tubes incorporated into the stiffening frame 40, the measuring tubes used, 40 inlet splitter or casserole splitter placed at the two ends of the stiffening frame and mechanically with the Meßrohrenden and the ends of the stiffening frame 40 connected, for example by welding.

In the embodiment, a substantially cylindrical stiffening frame is shown. Of course, this may alternatively be formed parallelepiped or in any other profile shape. Alternatively to the description Depending on the desired material properties, it is of course also possible to use other metals, for example aluminum or magnesium, when using stainless steel as the material of the casing of the stiffening frame. The metal foam can be made of various materials, such as stainless steel or based on magnesium, aluminum, titanium or zinc and their alloys.

Claims

claims

A mass flow meter for flowing media operating according to the Coriolis principle comprising a pair of substantially mutually parallel measuring tubes (2, 3), wherein the measuring tubes (2, 3) in an initial section (5) and in an end portion (11 ) are mechanically coupled together at least by a stiffening frame (4, 40) and held in a middle section (6 ... 10) between the start and end sections in a freely oscillating manner, with at least one exciter arrangement (23) acting on the two measuring tubes (2, 3). for generating mutually opposite oscillations of the two measuring tubes (2, 3), with at least one Coriolis forces and / or on Coriolis forces based vibrations detecting transducers (24, 25) for generating a measuring signal and with an evaluation device (26) which can be determined and output as a function of the measuring signal, a measured value of the flow, characterized in that the stiffening frame (4, 40), the mechanical hen coupling is provided in the beginning and end portion, to improve its rigidity at least partially filled with a metal foam (45) which is provided with recesses (21, 22) for carrying out the beginning and end section.

2. Mass flowmeter according to claim 1, characterized in that the two measuring tubes (2, 3) in the middle section (6 ... 10) are bent substantially U-shaped, that the starting and end portion of each measuring tube has a substantially straight inlet section or Outlet portion, which are arranged coaxially with each other, and an inlet manifold (5) and outlet manifold (11) for transfer from the inlet portion (4) on the first, substantially straight leg (6) of the U-shaped central portion or for the transfer of the second, substantially straight leg (10) of the U-shaped central portion of the outlet portion, and the two measuring tubes (2, 3) are connected to the stiffening frame at their inlet sections and at their outlet sections.

3. A method for producing a stiffening frame (4, 40) for a mass flow meter according to any one of claims 1 or 2, characterized in that a thin-walled metal plate to a substantially cylindrical tube

(41) is bent on the open tube ends sealing caps (42, 43) are placed, the cavity of the tube (41) is foamed with metal foam (45), the caps

(42, 43) removed from the pipe ends and recesses for the measuring tubes in the foam-filled tube (41) are incorporated.