Magnetic inductive flow meter having capacitive measuring device for empty pipe detection

Patent metadata

Field	Value
Publication number	US-9395220-B2
Application number	US-201314405309-A
Country	US
Kind code	B2
Filing date	Jul 23, 2013
Priority date	Jul 31, 2012
Publication date	Jul 19, 2016
Grant date	Jul 19, 2016

Abstract

A magnetoinductive flowmeter for measuring the flow rate of a flowing, conductive medium with a capacitive measuring apparatus for detecting empty pipes is provided. In order to improve the detection of empty pipes and, in particular, the capacitive coupling to the medium, the invention provides for the measuring apparatus for detecting empty pipes to comprise a sheet-like electrode in each case and a counterelectrode which form a measurement capacitance C Mess which is dependent on the medium and on the degree of filling of the measuring tube; for the measuring tube to have a wall thickness which is reduced in order to maximize the measurement capacitance C Mess at least in the region of the electrode and the counterelectrode; and for the measuring tube to be surrounded by a metal supporting housing, wherein, in order to maintain the pressure resistance of the measuring tube, a hollow-walled supporting body for minimizing the influence of parasitic capacitances on the measurement capacitance C Mess is arranged in each case in the region of the reduced wall thickness between the electrode and the inner wall of the supporting housing and between the counterelectrode and the inner wall of the supporting housing and supports the measuring tube against the supporting housing in each case.

First claim

The invention claimed is:

1. A magnetic inductive flow meter for measuring the flow of a flowing, conductive medium having a measuring tube made of a non-conductive material, having a magnetic field generating device for generating a magnetic field, in particular an alternating magnetic field, which penetrates the measuring tube essentially perpendicularly to the longitudinal axis of the measuring tube, having two measuring electrodes, in particular measuring electrodes that are galvanically coupled with the medium in order to tap a measuring voltage that is induced in the flowing medium, and having a capacitive measuring device for empty pipe detection, wherein the measuring electrodes are arranged along a connecting line that runs perpendicularly to the longitudinal axis of the measuring tube and perpendicular to the direction of the magnetic field, and wherein the compressive strength of the measuring tube is determined by the wall thickness or, respectively, the material thereof,
wherein the measuring device for empty pipe detection comprises an electrode and a counter electrode, each of which has a sheet-like design, which form a measurement capacity C Mess that is a function of the medium and of the fill level of the measuring tube;
the measuring tube has a reduced wall thickness at least in the region of the electrode and of the counter electrode in order to maximize the measurement capacity C Mess ;
that the measuring tube is encased by a supportive housing made of metal,
wherein in order to maintain the compressive strength of the measuring tube in the region of the reduced wall thickness between the electrode and the inner wall of the supportive housing, and between the counter electrode and the inner wall of the supportive housing, a support element having a hollow-walled design is arranged in each case in order to minimize the influence of parasitic capacitances on the measurement capacity C Mess , which support element in each case braces the measuring tube against the supportive housing.

2. The magnetic inductive flow meter according to claim 1 , characterized in that the measuring tube is made out of a thermoplastic,
including one of polyetheretherketone (PEEK), polyphenylene sulfide (PPS), perfluoroalkoxy alkane (PFA), polyvinylidene fluoride (PVDF), or of a glass fiber reinforced plastic, and in that the support element is made of the same or a similar material as the measuring tube.

3. The magnetic inductive flow meter according to claim 1 , wherein a strut is arranged inside the support element in order to increase the compressive strength.

4. The magnetic inductive flow meter according to claim 1 , wherein the electrode the counter electrode are spatially separated from the magnetic field generating device and from the measuring electrodes; in particular the electrode and the counter electrode on the one side, and the magnetic field generating device on the other side are consecutively arranged in the longitudinal direction of the measuring tube.

5. The magnetic inductive flow meter according to claim 1 , wherein a protective pad made of an elastic material is arranged between each of the electrodes and the support elements.

6. The magnetic inductive flow meter according to claim 5 , wherein the elastic material is made of rubber.

7. The magnetic inductive flow meter according to claim 1 , wherein the measuring tube has a wall thickness of less than 5 mm in the region of the measuring device for empty pipe detection.

8. The magnetic inductive flow meter according to claim 7 , wherein the wall thickness is 2 mm to 3 mm.

9. The magnetic inductive flow meter according to claim 1 , wherein the support element has a cap on each of end faces of the support element.

Assignees

• Ifm Electronic Gmbh

Inventors

• Reichart Walter
• Kreisel Christian
• Kriesen Ralf
• Körber Markus
• Liehr Sebastian
• Hoch Werner

Classifications

• G01F15/00

  Details of, or accessories for, apparatus of groups G01F1/00 - G01F13/00 insofar as such details or appliances are not adapted to particular types of such apparatus · CPC title

• G01F1/588

  combined constructions of electrodes, coils or magnetic circuits, accessories therefor · CPC title

• G01F1/584 Primary

  constructions of electrodes, accessories therefor · CPC title

• G01F15/14

  Casings, e.g. of special material · CPC title