Patent Application
20100037702
This application claims priority under 35 U.S.C. §119 to German Patent Application No. 10 2008 038 163.2 filed in Germany on Aug. 18, 2008, the entire content of which is hereby incorporated by reference in its entirety.
The present disclosure relates to a flowmeter having a measuring tube made of at least a plastic lining.
Flowmeters with different measuring principles are known. Chemically neutral to chemically aggressive media, and even occasionally abrasive media, are used as a measurement medium whose flow rate is to be determined. Together with chemical intervention, abrasive measurement media can not only contaminate the medium but also destroy electrically active surfaces, such as the surfaces of electrodes of a flowmeter, for example. Measuring tubes made of plastic or at least linings made of plastic, so-called liners, are often used for chemical resistance. However, progressive abrasion over the service life of a measuring device is a factor for consideration.
EP 1 193 474 A1 discloses flowmeters having a plastic measuring tube.
Against the problem described above, diagnosis of the state of the inner surface of the plastic can be an important consideration.
An exemplary embodiment of the present disclosure provides a flowmeter having a measuring tube internally lined with plastic. The exemplary flowmeter comprises at least one electrode arranged to be in contact with a measurement substance to be measured. In addition, the exemplary flowmeter comprises a plurality of layers arranged in a layered sequence of insulating plastic layers and conductive layers.
Additional features, advantages and refinements of the present disclosure are described below in greater detail with reference to exemplary embodiments illustrated in the drawings, in which:
Exemplary embodiments of the present disclosure provide a flowmeter which enables diagnosis or self-diagnosis of the state of the inner surface of the measuring tube.
According to an exemplary embodiment, a plastic measuring tube or a measuring tube internally lined with plastic is provided with a layer sequence of insulating plastic layers and conductive layers. The layer sequence makes it possible to diagnose the inner surface.
According to an exemplary embodiment, the conductive layers can comprise at least one metal layer.
According to an exemplary embodiment, the conductive layers can comprise at least one electrically conductive plastic layer.
According to an exemplary embodiment, the innermost layer arranged next to the measuring tube is an electrically insulating plastic layer, and the next layer lying over the innermost layer is a conductive layer. The conductive layer is contact-connected and is connected to an electric circuit or sources (e.g., battery or constant current supply) which signal an electrical short circuit to the measurement medium in the event of abrasion of the internal insulation layer. In this manner, abrasion detection can be accomplished in a very reliable manner.
However, it should be mentioned in this case that the definition of the term abrasion is broad. The term abrasion is used herein to mean not only creeping abrasion which occurs over a long service life but also damage which may occur if relatively large particles occasionally flow through the measurement medium. These may give rise to impacts and thus instantaneous damage to the inner layer of the measuring tube. This damage is likewise intended to be included in the definition of abrasion as used herein.
Another advantageous embodiment provides that the measuring tube, to the inside of which the alternating conductive and insulating layers are applied, is constituted by a metal tube. This makes it possible to use the advantageous statics and compressive strength of a metal tube.
According to another exemplary embodiment, the measuring tube to the inside of which the alternating conductive and insulating layers are applied, is constituted a plastic tube. This makes it possible to use the structural advantages of a plastic tube which is simple to handle and produce.
According to an advantageous embodiment, an insulation layer is arranged under conductive layer and a further conductive diagnostic layer is arranged under insulation layer. This enables a sensitive and diagnostically multilayer structure which can gradually determine progressive abrasion in thin layer sequences.
According to an exemplary embodiment, when a metal measuring tube is used, a further insulation layer can be arranged between the further conductive diagnostic layer and the inner wall of the basic measuring tube.
According to the exemplary embodiment employing plastic measuring tube, the further conductive diagnostic layer can be arranged directly on the inner wall of the measuring tube.
On the one hand, the strength of the measuring tube may be reduced by abrasion and this may become critical particularly in the case of plastic tubes. An alternating layer sequence of a plurality of conductive layers 2, 4 and nonconductive layers 3, 5 also makes it possible to detect progressive, increasingly ablating abrasion by contact-connecting conductive layers which alternate in the depth profile. In accordance with this configuration a corresponding signal relating to the respective contact between the various conductive layers 2, 4 and the measurement medium, respectively, can be used to determine a particular depth of abrasion that is reached. According to an exemplary embodiment, the nonconductive layers 3, 5 may be constituted by insulating plastic layers, for example.
This configuration enables detection of the depth of abrasion when it is no longer possible to clean the measuring tube as a result of progressive abrasion. For example, the problem of the suspension of sterility in food and pharmaceutics applications can be recognized in this case.
The depth profile of the coating sequence, as illustrated in
However, the principle is the same. With the metal tube 1′, two conductive diagnostic layers 2, 4 thus produce a layer sequence of five layers because there are three insulation layers 3, 5, 6, whereas, with the plastic measuring tube 1, there are only four layers because there are two conductive layers 2, 4 and tow insulating layers 3, 5. It is to be understood that the present disclosure is not limited to the number of layers illustrated in the examples of
The electrically conductive layers in both refinements may be metal layers, electrically conductive layers made of conductive plastic or even thin metal nets or grids, for example.
The individual electrically conductive layers 2, 4 in the internally lining layer sequence of the measuring tube 1, 1′ are contact-connected, for example, by means of vapor-deposited connecting lugs. The contact-connection is routed to outside of the measuring tube 1, 1′ and is connected to a measuring device. The latter detects a change in the conductivity or the electrical capacitance if the measurement medium comes into electrical contact with the conductive layer 2, 4 as a result of abrasion of the respective insulating covering layer 3, 5, or if a change in the capacitance needs to be detected in the case of capacitive measurement. In the case of capacitive measurement, the respective conductive layer 2, 4 acts like an electrode and the insulating layer 3, 5 applied thereto acts like a dielectric. It is thus possible, even in the case of an insulation layer 3, 5 which is becoming thinner, to detect a change before abrasion with electrical contact results.
In view of the above-described exemplary embodiments, features of the present disclosure can encompass and be applicable to the metal measuring tubes that have an insulating internal lining as well as plastic measuring tubes.
It will be appreciated by those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restricted. The scope of the invention is indicated by the appended claims rather than the foregoing description and all changes that come within the meaning and range and equivalence thereof are intended to be embraced therein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2008 038 163.2 | Aug 2008 | DE | national |
