Measuring and testing – Volume or rate of flow – By measuring electrical or magnetic properties
Patent
1997-12-17
2000-07-25
Noori, Max
Measuring and testing
Volume or rate of flow
By measuring electrical or magnetic properties
G01F 158
Patent
active
060924284
DESCRIPTION:
BRIEF SUMMARY
The invention concerns a device for determining the level of a conducting medium in a line, in particular for use in connection with a magnetic inductive flowmeter, with at least one capacitor plate, with an insulation layer between the capacitor plate and the medium, and with a control and evaluation circuit, the control and evaluation circuit acting upon the capacitor plate with an alternating voltage.
BACKGROUND OF THE INVENTION
The invention is particularly suited for use in a magnetic inductive flowmeter (MIF), in particular in an MIF with capacitively coupled electrodes. In the case of this combination, the capacitively coupled electrodes needed for the flow measurement by means of the MIF are used simultaneously as capacitor plates for determining the level. Furthermore, the combination of the present invention with an MIF is advantageous because it is not possible to distinguish between a reduced flow rate and a reduced level of the conducting medium from the measurement signal of an MIF.
Devices for determining the level of a conducting medium in a line in connection with an MIF with galvanically coupled electrodes are known from the prior art. These are also called idling identifications, i.e., the device can tell if the line is running dry. In the case of such an idling identification, the normal flow measurement of the MIF is used at the same time to check if the line is completely filled with the conducting medium. However, the operating principle of these known idling identifications fundamentally differs from that of the invention.
The processes and devices for determining the level of a medium in a line, known from European Offenlegungsschriften 0 514 964 and 0 547 751 as well as from the republished German Offenlegungsschrift 195 31 124, constitute the starting point of the present invention. In the case of these known processes and devices, the current between two capacitor plates always is evaluated for determining the level. This leads, as is evident from the above-mentioned prior art, to a division of the capacitor plates and relatively expensive control of the capacitor plates and evaluation of the measurement signals obtained. This problem results from the fact that the current between two capacitor plates is determined essentially by the electrical properties of the medium, therefore in particular the dielectric constant .epsilon. and the electric conductivity .sigma..
SUMMARY OF THE INVENTION
Thus the object of the invention is to make available a device for determining the level of a conducting medium in a line, which is designed simply and operates at least essentially independent of the electrical properties of the conducting medium.
The object indicated and derived previously is solved in accordance with the invention in that the control and evaluation circuit determines the capacitance between the capacitor plate and the medium as a measure for the level. Therefore, the phase portion of the conducting medium may be determined advantageously with the device in accordance with the invention by means of a corresponding control only of one capacitor plate. This capacitor plate at the same time also can form a capacitively coupled electrode of an MIF. In the case of a completely filled line, a capacitance is formed between the capacitor plate with a surface A and the conducting medium. Now if the line no longer is completely filled, this results in a smaller capacitance C.sub.Me.beta., which is proportional to a smaller surface A'. The smaller surface A' is obtained by projection of the surface A from the outside of the line onto the inside and consideration of only a part of this surface, which is wetted with the conducting medium. If the average thickness of the insulation layer between the capacitor plate and the conducting medium is designated as d and the dielectric constant of this layer is designated as .epsilon., the following is obtained for C.sub.Me.beta. : ##EQU1## and for C'.sub.Me.beta. : ##EQU2##
From this it is recognized that the capacitance between the capaci
REFERENCES:
patent: 3489007 (1970-01-01), Cushing
patent: 3991612 (1976-11-01), Mannherz et al.
patent: 3999443 (1976-12-01), Appel et al.
patent: 4036052 (1977-07-01), Searle
patent: 4483201 (1984-11-01), Haug
patent: 4785672 (1988-11-01), Picone
patent: 4972722 (1990-11-01), Hansen et al.
patent: 5018391 (1991-05-01), Doll
patent: 5400660 (1995-03-01), Doll
patent: 5421210 (1995-06-01), Kobayshi et al.
patent: 5544532 (1996-08-01), Brown
patent: 5625155 (1997-04-01), Yoshida
patent: 5641914 (1997-06-01), Doll
Kapazitive Fullstandsmessverfahren, J. Fehrenbach, (1990) pp. 102-111.
Krohne Messtechnik GmbH & Co. KG
Noori Max
Thompson Jewel V.
LandOfFree
Device for determining the phase component of a conductive mediu does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Device for determining the phase component of a conductive mediu, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Device for determining the phase component of a conductive mediu will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1328993