Electricity: measuring and testing – Electrical speed measuring – Including speed-related frequency generator
Patent
1994-10-06
1999-03-02
Snow, Walter E.
Electricity: measuring and testing
Electrical speed measuring
Including speed-related frequency generator
32420722, 324235, G01P 3487, G01P 3481, G01P 730
Patent
active
058776249
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND INFORMATION
The present invention relates to an arrangement for contactless measurement of the rotational speed of a component arranged on a shaft with several revolving magnets in whose magnetic fields a stationary pulse wire sensor is arranged.
Such a measuring arrangement is known from practice, in which a pulse wire sensor is activated by the magnetic fields of several magnets which are arranged on the circumference of a rotating component. A pulse is triggered when the components of the magnetic fields parallel to the sensor exceed a certain minimum value.
According to the known laws of induction moving magnetic fields generate in their vicinity in conducting surfaces a changing magnetic flux which generates eddy currents. Similar to mechanical bearing friction such eddy currents represent an electrical stray current.
In certain applications, the eddy currents have a disruptive effect. For example, with turbine gas flowmeters there is only a very small driving torque to rotate the metering wheel at minimum flow. Therefore, the eddy currents lead to measuring errors in the lower measuring range.
Therefore, the object of the present invention was to develop a measuring arrangement of the aforementioned type which provides reliable measurements irrespective of the rotational speed, particularly in the lower measuring range.
SUMMARY
The superposition of the individual magnetic fields of the magnets of alternatingly opposite polarity results in a large field component parallel to the axis of the pulse wire sensor, overall the stray field outwards being small. A small magnetic field strength can therefore be selected.
The measuring arrangement is unaffected by rotational speed, i.e. a minimum rotational speed is not required, therefore the measuring range is large.
The position of the pulse wire sensor relative to the magnets can be easily optimised to the pulse height. The same applies to the distance between the magnets.
Without any electricity supply the measuring arrangement provides a high pulse voltage which can be transmitted free from interference to an electronic evaluation and display system.
It is particularly advantageous to use two bar-shaped magnets which are aligned parallel to each other.
A further advantageous embodiment of the present invention consists in the magnets being embedded in the shaft of the component.
This measure ensures that the area interspersed by the magnetic flux is kept to a minimum. The arrangement ensures the pulse wire sensor is actuated with position tolerance being uncritical and that the eddy currents are simultaneously minimised.
Combinations of the inventive features which deviate from the combinations mentioned hereinabove are deemed to have been disclosed as essential to the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention is now explained in greater detail using one application of the inventive measuring arrangement together with the attached drawing.
FIG. 1 shows a section through a measuring arrangement in a turbine gas flowmeter.
FIG. 2 shows a schematic of the form of the magnetic field of the measuring arrangement.
DETAILED DESCRIPTION
Referring to FIG. 1, a bearing body 2 is accommodated in a housing 1, said bearing body carrying a measuring wheel shaft 3 of a measuring wheel 3a. Two bar-shaped magnets 4 are embedded in the measuring wheel shaft 3 at a distance to each other such that their poles N, S are radially aligned. The magnets 4 are substantially parallel to each other and have opposite polarity.
A pulse wire sensor 5 is arranged parallel to the rotational axis of the measuring wheel shaft 3 in a position to the bar-shaped magnets 4 which is optimised to the pulse height. The pulse wire sensor 5 is connected to an electronic evaluation and display system 6 by means of lines 7.
As shown schematically in FIG. 2, the two magnetic fields 8 simultaneously pulse the pulse wire sensor 5. This results in a superposition of the individual magnetic fields of the magnets 4, a large field component parallel to t
REFERENCES:
patent: 3832634 (1974-08-01), Galea
patent: 4525670 (1985-06-01), Miyagawa et al.
patent: 4646088 (1987-02-01), Inoue
patent: 4772813 (1988-09-01), Mohri et al.
Kettner Thomas
Loetz-Dauer Volker
Elster Produktion GmbH
Snow Walter E.
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