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Optimized Electrode Shield Used on Electromagnetic Flowmeters

IP.com Disclosure Number: IPCOM000191851D
Published in the IP.com Journal: Volume 10 Issue 2A (2010-02-12)
Included in the Prior Art Database: 2010-Feb-12
Document File: 2 page(s) / 550K

Publishing Venue

Siemens

Related People

Juergen Carstens: CONTACT

Abstract

Flow sensors of electromagnetic flowmeters in some cases are filled with a molding material e.g. PUR (polyurethane). When the measuring tube is internally pressurized the measuring electrode can move outward due to a void within the Faraday cage (electrode shield). The back of the Faraday cage is supported by the molding material (see Figure 1). This electrode movement will de-stabilize the measuring signal. It is essentially to have no electrode movement since it will change the cross sectional area. A change in the cross sectional area will change the calibration factor, and thereby reduce the performance of the flowmeter. In worst case the electrode can penetrate through the liner and into the reinforcement net, and thereby the measuring electrode will be grounded. In addition, it is not possible to eliminate the void in the Faraday cage purely by height reduction due to height variation of the electrode "potting". For some measuring applications a higher working pressure is required. Up to now, the existing flow sensor working pressure is limited to nominal pressure PN16.

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Optimized Electrode Shield Used on Electromagnetic Flowmeters

Idea: Craig Nicholson, GB-Stonehouse; Stephen Means, GB-Stonehouse; Morten Frost Lorenzen,
DK-Nordborg

Flow sensors of electromagnetic flowmeters in some cases are filled with a molding material e.g. PUR (polyurethane). When the measuring tube is internally pressurized the measuring electrode can move outward due to a void within the Faraday cage (electrode shield). The back of the Faraday cage is supported by the molding material (see Figure 1). This electrode movement will de-stabilize the measuring signal. It is essentially to have no electrode movement since it will change the cross sectional area. A change in the cross sectional area will change the calibration factor, and thereby reduce the performance of the flowmeter. In worst case the electrode can penetrate through the liner and into the reinforcement net, and thereby the measuring electrode will be grounded. In addition, it is not possible to eliminate the void in the Faraday cage purely by height reduction due to height variation of the electrode "potting". For some measuring applications a higher working pressure is required. Up to now, the existing flow sensor working pressure is limited to nominal pressure PN16.

The molding material becomes saturated with moisture in service. It is imperative that there is no conductive path to the measuring electrode. The existing Faraday cage will allow ingress of molding material in close vicinity of the potted measuring electrode. The potting is domed to give maximum insulation between measuring electrode and the saturated molding...