Electricity: measuring and testing – Magnetic – Displacement
Patent
1984-06-05
1987-06-23
Eisenzopf, Reinhard J.
Electricity: measuring and testing
Magnetic
Displacement
324239, 324227, 336 45, 34087031, G01B 710, G01N 2772, G01R 3312
Patent
active
046756035
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an inductive position and motion sensor. More particularly this invention concerns such a sensor used as an input for a control system.
BACKGROUND OF THE INVENTION
A standard such inductive sensor has an outer fixed field winding energized by alternating current and a coaxial inner detecting winding that is displaceable axially in the field winding and that has no ferromagnetic core. A link arrangement axially displaces the inner winding with the object whose position is being detected. The voltage induced in the detecting winding is used to establish the position of the thing whose position or motion is being detected, the absolute value of the voltage indicating position and the slope of the voltage/time curve indicating displacement speed.
As a result of the inevitable internal and external disturbances of the magnetic field as well as of the nonhomogeneous form of the magnetic field, the sensitivity of these devices does not satisfy strict requirements. For instance changes in temperature can change the conductivity of the wire of the coils, affecting their inductance, or variations in the voltage or frequency of the feed current may be reflected in the readings. Only the most complex and hence failure-prone circuits can repress the effects of outside disturbances enough to make such a sensor highly accurate.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to provide an improved motion and position detector.
Another object is the provision of such a motion and position detector which overcomes the above-given disadvantages, that is which gives highly accurate readings while remaining of fairly simple construction.
SUMMARY OF THE INVENTION
An apparatus for determining the position of an object according to the invention has an outer fixed field winding extending along an axis, a source for energizing the field winding with alternating current and thereby creating a magnetic field, and an inner coreless detecting winding displaceable coaxially in the field winding. Thus the field induces a voltage in the inner winding. A link displaces the detecting winding axially in the field winding with the object and thereby changes the voltage induced by the field in the detecting winding. An equalizing winding coaxialy between the field winding and the detecting winding is fixed in the field winding. The field also induces a voltage in the equalizing winding. An electronic unit divides the voltages induced in the detecting and equalizing windings into each other and derives a detection signal corresponding to the position of the object and inner winding relative to the outer winding.
Thus according to this invention expensive and inefficient shielding is not used to eliminate the outside disturbances, nor are complex circuits employed to compensate for them. Instead the detection signal is altered by another signal that will be affected substantially identically by the disturbances, so same can be canceled out easily.
According to another feature of this invention, external resistances are connected to the equalizing and detecting windings and are of an ohmage such that they hold the currents of the voltages of the detecting winding and equalizing windings to less than one-hundredth, preferably one-thousandth, of the current of the field winding. This greatly increases accuracy.
According to another feature of this invention the detecting winding is axially at least one-fifth longer than the field winding. The equalizing and field windings are of the same axial length and generally identical. In addition soft-iron rings at the ends of the field coil suppress stray fields.
The link of this invention is a rod passing along the axis through the housing and carrying the detecting coil. A pivot and crank arrangement can move this rod axially in response to anything resembling straigt-line or arcuate movement in virtually any direction near the detecting apparatus of this invention.
DESCRIPTION OF THE DRAWING
The above and o
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Edmonds Warren S.
Eisenzopf Reinhard J.
Rudolf Schmidt, Armaturen- u. Gusswerk Gesellschaft mbH
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