Electricity: measuring and testing – Magnetic – Displacement
Patent
1994-09-16
1996-08-13
O'Shea, Sandra L.
Electricity: measuring and testing
Magnetic
Displacement
3242072, 327513, G01B 704, G01B 730, H03K 338
Patent
active
055459838
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a displacement sensor which comprises a magnet and magnetoelectric conversion means for sensing the variation of magnetism caused by the magnet, and senses the displacement of a magnetic material to be measured, such as iron.
BACKGROUND OF THE INVENTION
Sensing the location of a magnetic material or magnet by using magnetoelectric conversion elements such as Hall elements or magnetic resistance elements has been a widely practiced method, for example, in sensing the phase of a DC brushless motor. However, even a GaAs Hall element, which usually has a small temperature coefficient, has a temperature coefficient of -0.06%/.degree.C. during constant-current drive. Therefore, the displacement could not be accurately sensed in a wide temperature range.
In order to overcome this problem: 38073/1981) provides a compound magnetoelectric conversion means which is composed of Hall elements and a temperature sensing element all closely placed on a base material in the same pattern, and which is thereby capable of performing excellent temperature compensation even for local temperature variations in the element itself. of output voltage caused by the temperature variations of the Hall elements are controlled by forming compensation resistors in series on a base member. obtaining a high precision throttle sensor that is independent of temperature variations, with the polarities of the temperature coefficients of the magnet and the Hall elements opposite to each other.
Although the compound magnetoelectric conversion elements described in 1) and 2) are excellent in temperature compensation, the production of these compound magnetoelectric conversion elements is difficult and costly.
Furthermore, these compound magnetoelectric conversion elements are not generally used, and therefore hard to come by.
In a displacement sensor comprising a permanent magnet and megnetoelectric conversion elements as described in 1) and 2), the surface magnetic flux density of the permanent magnet itself has temperature characteristics, and therefore, compensation only for the temperature characteristics of the magnetoelectric conversion elements is not enough to compensate for the temperature characteristics of the whole displacement sensor.
In the case of 3), the problem is the difficulty in adjusting the temperature coefficients of the magnet and the Hall elements so that they are opposed to each other. Though Si Hall ICs are used in place of Hall elements to provide a switching sensor, the electron mobility of Si is so small that the swicthing sensor is not suitable for a high precision sensor. Further, Si Hall ICs have a large offset voltage, which causes variations in temperature characteristics.
Thus, the displacement sensor the prior art is not capable of performing accurate sensing due to temperature variations and is not suitable for the use in a wide temperature range.
Accordingly, the present invention is basically aimed at providing a displacement sensor that is capable of accurately sensing the displacement in a wide temperature range by compensating for the temperature coefficients of a permanent magnet and magnetoelectric conversion elements. Even when the displacement sensor is used in a place where the temperature varies greatly, the displacement is sensed with high precision by the displacement sensor.
SUMMARY OF THE INVENTION
A displacement sensor of the present invention comprises a magnet and magnetoelectric conversion means for sensing the variation of magnetism cuased by the magnet to sense the displacement of the magnetic material to be measured. In this displacement sensor, a first magnetoelectric conversion means is located in the place where the magnetic flux density is varied by the displacement of the magnetic material to be measured, while a second magnetoelectric conversion means of the same type as the first magnetoelectric conversion means is located in the place where the magnetic flux density is not varied. A circuit means for adding the output
REFERENCES:
patent: 3634799 (1972-01-01), Strauch
patent: 4893027 (1990-01-01), Kammerer et al.
patent: 4970463 (1990-11-01), Wolf et al.
patent: 5128613 (1992-07-01), Takehashi
patent: 5402064 (1995-03-01), Eck et al.
Ito Norio
Okeya Makoto
Ueki Yasunori
O'Shea Sandra L.
Phillips Roger
Seiko Epson Corporation
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