Electrical resistors – Resistance value responsive to a condition – Magnetic field or compass
Statutory Invention Registration
1998-12-23
2001-09-04
Pihulic, Daniel T. (Department: 3662)
Electrical resistors
Resistance value responsive to a condition
Magnetic field or compass
Statutory Invention Registration
active
H0001990
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to Hall effect devices and, more particularly, to Hall effect transducers and sensors having a magnetic shunt device associated therewith to null the magnetic field when the magnetic field is parallel to the sensitive face of the Hall effect device.
BACKGROUND ART
If exposed to a magnetic field, a current carrying Hall effect device typically produces an output voltage that is proportional to both the electric current and the sine of the angle between the magnetic field and the direction of the current flowing through the Hall effect device. That is, if there is no magnetic field, or if the magnetic field is parallel to the current direction flowing through the Hall effect device, in other words, the angle between the magnetic field and the current direction is zero, then the output voltage of the Hall effect device is either zero, or some null or quiescent output voltage. For a given electric current magnitude, the output voltage of the Hall effect device reaches its maximum value when the magnetic field is perpendicular (+90° and −90°) to the direction of the current.
In order to avoid reversal of the Hall effect output voltage as the magnetic field varies from −90° to +90° around the Hall effect device, linear Hall effect manufacturers bias the Hall effect output voltage such that minimum voltage is obtained when the magnetic field is at −90° and maximum voltage (V) is obtained when the magnetic field is at +90°. Therefore, in this arrangement, in the absence of the magnetic field, or if the magnetic field is parallel to the current direction, that is, the angle between the magnetic field and direction of current is zero, a linear Hall effect device should produce an output voltage at this null or “no action” position that is about half the voltage output (V/2) of the device.
In some linear Hall effect transducer applications, the Hall effect device output voltage is varied from its minimum value to its maximum value by rotating the magnetic field around the Hall effect device at a fixed, optimal distance. In this particular application, no magnetic field, or zero angle between the magnetic field and the direction of current of the Hall effect device, should produce the exact same output voltage. However, if the “at rest” position, or “no action” position, of the Hall effect device relative to the rotating magnetic field corresponds to the zero angle position therebetween, it may be difficult to mechanically center the magnetic field so that the angle between the magnetic field and the direction of current through the Hall effect device is precisely zero for every linear device produced. To attempt this mechanical centering procedure is both tedious and costly when a large number of linear Hall effect devices are to be produced. In order to circumvent this problem, potentiometers and other devices are traditionally added to the electronic circuitry associated with the Hall effect device to manually adjust the output voltage of such devices for the zero angle position.
It is, therefore, desirable to provide an easy way to null the affect of the magnetic field in a Hall effect sensor application when the magnetic field is parallel to the sensitive face of the Hall effect device.
It is also desirable to provide a Hall effect device that does not require additional electronic circuitry to adjust its output voltage at the zero angle or null position.
Still further, it is likewise desirable to ensure that the null output voltage of the Hall effect device in a particular application is consistent for a large number of such devices used in the same application despite mechanical uncertainties in accurately arranging the magnet(s) or electromagnet(s) and the Hall effect device at the zero angle or “no action” position.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.
DISCLOSURE OF THE INVENTION
In accordance with the teachings of the present invention, one embodiment of a Hall effect sensor is disclosed wherein a magnetic shunt device of appropriate size and dimension is positioned around a Hall effect device to null the magnetic field when this field is parallel to the sensitive plane of the Hall effect device. This shunt configuration ensures a consistent null output voltage for a large sample of similar devices despite mechanical positioning uncertainties and misalignment problems which arise during construction and manufacturing relative to the proper orientation of the magnetic devices that generate the magnetic field and the Hall effect device at the zero angle or “no action” position.
REFERENCES:
patent: 3471844 (1969-10-01), Schugt
patent: 3787769 (1974-01-01), Parkinson
patent: 3818326 (1974-06-01), Masuda et al.
patent: 4124814 (1978-11-01), Lauerman
Kherat Samir M.
Rector Stephen W.
Caterpillar Inc.
Green Clifton
Pihulic Daniel T.
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