Measuring and testing – Volume or rate of flow – By measuring electrical or magnetic properties
Patent
1992-11-16
1995-09-12
Chilcot, Jr., Richard E.
Measuring and testing
Volume or rate of flow
By measuring electrical or magnetic properties
7386111, G01F 158
Patent
active
054489202
DESCRIPTION:
BRIEF SUMMARY
The invention concerns a device for inductively measuring the state of a stream of electrically conductive liquid in a flow channel that contains, in an isolated section of the channel, a pair of electrodes opposite one another over the cross section of the channel, in or on the wall, that make contact with the liquid, and a magnetic field generating system to excite a changing magnetic field passing through the liquid stream, wherein the electrodes are connected to a display or recording device via a signal transmission arrangement.
Determining the state of a stream of electrically conductive liquid in a flow channel is understood to mean both measuring the inductive flow and inductively finding the height of the cross section of the liquid stream when the cross section of the channel is not completely filled.
In a device of the type generally considered here, if the flow is to be measured inductively, a magnetic field generating system is used that generates magnetic field lines that pass through the flow channel roughly parallel to the plane of the cross section of the channel containing the electrodes and diagonally to the connecting line between the electrodes.
On the other hand, if the height of the liquid stream in a cross section of the channel that is not completely full is to be found inductively, the field lines of the magnetic field generating system pass through the flow channel in a direction parallel to the axis of the flow channel. In any case, the magnetic field is alternating or pulsing.
If the cross section of the flow channel is not completely filled with the stream of liquid, then changing the conductive cross section causes the induced electrical field lines to move between the electrodes in the liquid stream, so that there is a difference in potential between the electrodes, from which a display of the height of the liquid stream in the flow channel can then be derived.
The magnetic field lines, which run basically parallel to the axis in the flow channel, and the accompanying stray fields induce voltages, both in the volume of liquid and in the conductive parts of the surrounding structure, especially in the signal transmission arrangement where the electrodes are connected to the display and recording device; such voltages are in phase at the measurement voltage in question, depending on the changing height of the liquid stream, but actually have nothing to do with this measurement signal, distort it and cannot be eliminated by phase-selective filtering.
When such noise voltages, caused primarily by induced voltages in the signal transmission arrangement, assume rather substantial proportions, the measurement signal in question can be drowned out, so that the device in question for inductively measuring the height of the liquid stream in the flow channel is unusable, or very expensive designs must be used.
The aforementioned problems also apply to devices for measuring inductive flow with a magnetic field generating system in which the field lines generated basically run transversely through the flow channel, to the extent that these magnetic field generating systems, because of their design or because of directional errors or even because of asymmetries that occur during operation, have magnetic field components that are parallel to the longitudinal axis of the flow channel. This is true to a very great extent in all practical cases. Because magnetic alternating fields or pulsing magnetic fields are also used for inductive flow meters and because of the need to provide a signal transmission arrangement to connect electrodes diametrically opposite one another to the display and recording device, there are also conductive loops on conventionally designed inductive flow meters in which those axial components of the magnetic alternating field or pulsing magnetic field induce noise voltages which distort the measurement results.
The task of the invention is therefore to design a device for inductively measuring the state of a current of electrically conductive liquid in a flow channel,
REFERENCES:
patent: 3795140 (1974-03-01), Nishihara
patent: 3805161 (1974-04-01), Bayha et al.
patent: 4338815 (1982-07-01), Peters et al.
Ketelsen Andres
Ketelsen Broder
Chilcot Jr. Richard E.
Dougherty Elizabeth L.
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