Position measuring apparatus

Claim 2

Apparatus adapted to be used to measure movement of an element comprising: a differential transformer having a primary coil, which is adapted to have a source of alternating current connected thereto, and two secondary coils spaced from one another; a slug of a magentic material which is adapted to be connected to the element to be measured and to be moved relative to and adjacent said secondary coils; means connecting said secondary coils in electrical opposition to one another; and a measuring circuit connected to said secondary coils, said measuring circuit including rectifying means to establish a DC output signal representative of an AC signal established across said secondary coils, amplifying means connected to said rectifying means, said amplifying means having a nonlinear response to a DC input signal such that the gain of the amplifying means increases when the input signal decreases, and a meter connected to said amplifying means.

Claim 5

The apparatus of claim 2 wherein said amplifier comprises an operational amplifier having a transistor connected in a feedback network between the output and the input of the amplifier, said transistor comprising an emitter, a collector and a base, the collector being connected to said input, the emitter being connected to said output and the base being connected to a point of reference potential.

Claim 6

The apparatus of claim 1, further comprising a scale positioned so as to permit the location of said transformer to be measured when said slug is symmetrically positioned to said secondary coils.

Claim 7

In a system adapted to measure the compressibility of a test element in which the test element is positioned in a housing containing a hydraulic fluid, a movable piston is located in an opening of the housing, and pressure is exerted on the piston from an external source to exert a corresponding pressure on the hydraulic fluid in the housing; apparatus to measure movement of the piston comprising: a movable differential transformer spaced from said piston, said transformer including a primary coil, which is adapted to have a source of alternating current connected thereto, and two secondary coils spaced from one another; a slug of magnetic material; means connecting said slug to said piston so that movement of said piston results in movement of said slug relative to and adjacent said secondary coils; means connecting said secondary coils in electrical opposition to one another; and a measuring circuit connected to said secondary coils, said measuring circuit including rectifying means to establish a DC output signal representative of an AC signal established across said secondary coils, amplifying means connected to said rectifying means, said amplifying means having a nonlinear response to a DC input signal such that the gain of the amplifying means increases when the input signal decreases, and a meter connected to said amplifying means.

Claim 8

In a system adapted to measure the compressibility of a test element in which the test element is positioned in a housing containing a hydraulic fluid, a movable piston is located in an opening of the housing, and pressure is exerted on the piston from an external source to exert a corresponding pressure on the hydraulic fluid in the housing; apparatus to measure movement of the piston comprising: a movable differential transformer spaced from said piston, said transformer including a primary coil, which is adapted to have a source of alternating current connected thereto, and two secondary coils spaced from one another; a slug of magnetic material; means connecting said slug to said piston so that movement of said piston results in movement of said slug relative to and adjacent said secondary coils; means connecting said secondary coils in electrical opposition to one another; and a measuring circuit connected to said secondary coils, said measuring circuit including rectifying means to establish a DC output signal representative of an AC signal established across said secondary coils, amplifying means connected to said rectifying means, said amplifying means having a nonlinear response to a DC input signal such that the gain of the amplifying means increases when the input signal decreases, and a meter connected to said amplifying means.

Claim 9

The apparatus of claim 5 wherein said amplifying means comprises an amplifier having a logarithmic response.

Claim 10

The apparatus of claim 5, further comprising a scale positioned so as to permit the location of said transformer to be measured when said slug is symmetrically positioned relative to said secondary coils.