GB2312282A

GB2312282A - Vibration decoupling in mass flow measuring device

Info

Publication number: GB2312282A
Application number: GB9707145A
Authority: GB
Inventors: Yousif A Hussain; Chris N Rolph
Original assignee: Krohne AG
Current assignee: Krohne AG
Priority date: 1996-04-15
Filing date: 1997-04-08
Publication date: 1997-10-22
Anticipated expiration: 2017-04-08
Also published as: DE19614736A1; DE19614736C2; GB2312282B; GB9707145D0

Description

"MASS FLOW M[EASURING DEVICE" This invention relates to a mass flow

measuring device for flowing media, which operates based on the Codolis principle, having at least one vibrating Coriolis line conveying the flowing medium, having a housing which encloses the Coriolis line at least, and having attachments on the housing.

Mass flow measuring devices for flowing media which operate based on the Coriolis principle are known in a multiplicity of designs. There exists a multiplicity of proposals, which are almost impossible to survey, for the optimum course of the Codolis line. In order to achieve the desired effect in the Coriolis line due to the flowing medium, the Codolis line has to be in a state of vibration. A vibration generator, and frequently even a plurality of vibration generators, is used for this purpose. In mass flow measuring devices of this type, the mass flow of the flowing medium through the Coriolis line is determined by a quantitative evaluation of the Codolis force acting on the Coriolis line which is in a state of vibration. Since, as a general rule, the Coriolis forces arising are very small, mass flow measuring devices of this type are particularly sensitive to the coupling or decoupling of mechanical energy between the mass flow is measuring device and its surroundings. In the past, considerable attention has been paid to the coupling between the mass flow measuring device and the pipelines attached to the mass flow measuring device; this has resulted in a multiplicity of proposed solutions aimed at reducing this mechanical coupling.

The coupling between the Coriolis line and the housing which generally encloses the vibration generator or generators and the measurement recorder or recorders has also already been the subject of improvements. The common approach in this respect consists of ensuring very pronounced decoupling between the Codolis line and the housing by setting the resonant frequency of the housing so that it is as different as possible from the frequency of vibration of the Coriolis line. For this purpose, the housing is generally constructed so that it is very resistant to vibration.

A problem which has hitherto received no consideration is the mechanical coupling between firstly the Coriolis line or the housing and secondly various attachments on the housing of the mass flow measuring device.

A basic unit, i.e. a unit consisting of a Coriolis line, a vibration generator, a measurement recorder and a housing, frequently serves as the basis for a plurality of different purposes of use of suitable mass flow measuring devices. Depending on the purpose of use, various attachments are mounted on the mass flow measuring device or on the housing thereof. The mounting of such attachments on the housing, which is generally effected in an undefined manner, results in mechanical coupling effects between systems which are capable of vibration, which can affect the accuracy of measurement of the mass flow measuring device to a considerable extent. These unwanted effects cannot even be prevented by an appropriate design of the attachments, since is the mechanical couplings are frequently also influenced by the actual installation situation on site, which understandably cannot be taken into consideration constructionally in each case. As a result, the effects which determine the vibration properties in known mass flow measuring devices cannot therefore be fixed from the outset by a corresponding construction, so that the accuracy of measurement of the mass flow measuring device is already impaired by the unsatisfactory definition, as a system capable of vibration, of the mass flow measuring device as a whole.

The underlying object of the present invention is therefore to improve the known mass flow measuring devices for flowing media which operate based on the Coriolis principle so that the vibrational properties of the unit as a whole remain substantially constant irrespective of different attachments, so that an increased accuracy of measurement is ensured.

The object introduced and illustrated above is achieved according to the invention in that at least a part of the attachments is joined to the housing via vibrational decoupling means. This measure according to the invention ensures a defined vibrational behaviour of the mass flow measuring device, since the undefined influences of the attachments have no effect, or have only a slight effect, on the vibrational behaviour as a whole. The vibrational decoupling means are designed according to known physical principles so that as far as possible no vibrational coupling or only a slight vibrational coupling is present between the attachments and the housing.

For economic reasons, springs are particularly suitable as vibrational decoupling means.

These are simple to manufacture and adapt and are available in a multiplicity of forms of construction matched to the respective purpose of use.

The vibrational decoupling between the attachments and the housing is particularly advantageous for attachments of large mass, such as electronic evaluation units for example, is attachments comprising external abutments, such as cables or cable conduits for example, and attachments having vibrational properties which are particularly undefined, such as means for heating the mass flow measuring device.

In detail, a multiplicity of possibilities exist as regards fashioning and further developing the mass flow measuring device for flowing media according to the invention which operates based on the Coriolis principle. Reference is made in this respect firstly to the claims which are subordinate to claim 1 and secondly to the description given below of a preferred embodiment in association with the drawings, which are as follows:

Figure 1 is a schematic illustration which explains the principle according to the invention; and Figure 2 shows an example of an embodiment of a joint according to the invention between a housing and an electronic evaluation unit.

Figure 1 of the drawings illustrates a mass flow measuring device for flowing media which operates based on the Coriolis principle. This schematic illustration only comprises the housing 1, an attachment 2 which is not specified in detail, and a vibrational decoupling means 3 according to the invention which joins the housing 1 to the attachment 2. The vibrational decoupling according to the invention between the housing 1 and the attachment 2 is ensured by selecting the spring properties and damping properties of the vibrational decoupling means 3 so that they are matched to the housing 1 and to the attachment 2.

In addition, the drawing of Figure 2 shows a particular embodiment of a mass flow measuring device for flowing media according to the invention which operates based on the Coriolis principle. Figure 2 merely illustrates a portion of this embodiment in section. A base 4 is fixed to the housing 1 via a welded joint 5. An electronic evaluation unit 6, only a portion of which is illustrated, is joined to the base 4 via a connection which acts as a spring in the axial direction. The spring unit 7 forms a central element of this connection. Depending on the requirements, this spring unit 7 may consist of one or more spring washers, one or more coil springs or one or more leaf springs. In this respect, the spring unit 7 is designed in each case so that it ensures maximum vibrational decoupling.

The measure according to the invention only justifies the expense associated therewith in the situation where the attachment concerned has a significant influence on the accuracy of -5measurement of the mass flow measuring device. Thus it is not always necessary to join all attachments to the housing via vibrational decoupling means.

Claims

1. A mass flow measuring device for flowing media, which operates based on the Coriolis principle, having at least one vibrating Coriolis line conveying the flowing medium, having a housing which encloses the Coriolis line at least, and having attachments on the housing characterised in that at least a part of the attachments is joined to the housing via vibrational decoupling means.

2. A mass flow measuring device according to Claim 1, wherein the vibrational decoupling means are constructed as springs.

3. A mass flow measuring device according to Claim 1 or 2, wherein electronic evaluation units, cables, cable conduits and/or means for heating the mass flow measuring device are joined to the housing via vibrational decoupling means.

4. A mass flow measuring device substantially as hereinbefore described with reference to the accompanying drawings.