Three-terminal capacitive servomechanism

Claim 2

A servomechanism comprising in combination: a three-terminal transmitting capacitor including a transmitter driven element, a transmitter receptor element, and a transmitter ground terminal; a three-terminal receiving capacitor including a receiver driven element, a receiver receptor element and a receiver ground terminal; first circuit means for applying drive signals of predetermined AC voltage level to each of said driven elements; second circuit means, including at least one high gain amplifier with a capacitive feedback loop, to maintain both of said receptor elements at virtual ground and produce an error signal responsive to the difference in feed-through capacitance, AC voltage level product of said transmitting and receiving capacitors; third circuit means coupled to said ground terminals for shielding said first circuit means for said second circuit means; and control means responsive to said error signal and operably connected to cause a change in the feed-through capacitance of said receiving capacitor in a direction to minimize said error signal.

Claim 3

The servomechanism of claim 1 wherein the second circuit means includes a synchronous demodulator synchronized with said AC drive signals to provide an output signal substantially unaffected by shunt conductance present between the elements of said capacitors.

Claim 4

The servomechanism of claim 1 wherein said control means includes an AC servo amplifier responsive to said error signal and a two phase AC motor having a control winding and a reference winding and wherein the current in said reference winding is 90* out of phase with the current in said control winding caused by the presence of said error signal.

Claim 5

The servomechanism of claim 1 wherein the said drive signals include a first drive signal of one phase and a second drive signal of opposite phase and wherein said first circuit means conducts one of said drive signals to said transmitter driven element and the other of said drive signals to said receiVer driven element.

Claim 6

The servomechanism of claim 1 wherein electrical drive signals of the same amplitude and phase are conducted to each of said transmitter and receiver driven elements, and wherein said second circuit means includes a first high gain amplifier having a capacitive feedback loop and connected at an input to said transmitter receptor element, a second high gain amplifier having a capacitive feedback loop and connected at an input to said receiver receptor element, an inverting amplifier connected at an input to the output of one of said first and second high gain amplifiers, and combining means connected between the output of said inverting amplifier and said other of said first and second high gain amplifiers to combine the output signals therefrom and provide said error signal.

Claim 7

The servomechanism of claim 4 wherein said second circuit means includes a first high gain amplifier having a capacitive feedback loop and connected at an input to one of said transmitter and receiver receptor elements, a second high gain amplifier having a capacitance feedback loop and connected at an input to the other of said transmitter and receiver receptor elements, and means connected to the outputs of said first and second amplifiers to combine the output signals therefrom and provide said error signal.

Claim 8

The servomechanism of claim 1 wherein each of said transmitting and receiving capacitors are positional transducers, so that the position of said transmitting capacitor represents a servomechanism input, and the position of said receiving capacitor represents a servomechanism output.

Claim 9

The servomechanism of claim 7 wherein a plurality of positional transducers connected in parallel with each other provide the capacitance for said transmitting capacitor.

Claim 10

The servomechanism of claim 7 further including indicating means connected to said control means to provide an indication of the angular position of said receiving capacitor.

Claim 11

The servomechanism of claim 1 wherein each of said transmitting and receiving capacitors are variable differential capacitors.

Claim 12

The servomechanism of claim 10 wherein each of said transmitting and receiving differential capacitors are positional transducers so that the position of said transmitting differential capacitor represents a servomechanism input, and the position of said receiver differential capacitor represents a servomechanism output.

Claim 13

The servomechanism of claim 1 wherein said transmitting capacitor is a level probe with its feed-through capacitance responsive to level of a material, and further including indicating means connected to said control means to provide an indication of said level.

Claim 14

The servomechanism of claim 12 wherein said second circuit means includes a synchronous demodulator for substantially cancelling the effect of conductance from said error signal.

Claim 15

The servomechanism of claim 1 wherein said servomechanism provides control of material level in a tank and said receiving capacitor includes a level probe mounted in a tank so that its feed-through capacitance is responsive to the level of material in the tank, and wherein the transmitting capacitor is a level setting capacitor with its receptor element connected in parallel with said receiver receptor element, and wherein said control means includes a valve connected between said tank and a source of material and responsive to said error signal to add material to said tank.

Claim 16

The servomechanism of claim 14 wherein said second circuit means includes a synchronous demodulator for substantially cancelling the effect of conductance from said error signal.

Claim 17

The servomechanism of claim 1 wherein said transmitting capacitor is a dielectric constant probe and further including means connected to said control means to provide an indication of the dielectric properties of a material that may be in proximity to said probe.

Claim 18

The servomechanism of claim 16 wherein said second circuit means includes a synchronous demodulatoR for substantially cancelling the effect of conductance from said error signal.

Claim 19

The servomechanism of claim 1 wherein said servomechanism provides control of the ingredients ratio of two materials in a container; wherein said receiving capacitor includes a dielectric probe mounted in said container so that the feed-through capacitance of said probe is responsive to the dielectric properties of said materials, and ratio setting transmitting capacitor; and wherein said control means includes a valve controlling the flow of at least one of said materials into said container.

Claim 20

The servomechanism of claim 18 wherein said second circuit means includes a synchronous demodulator for substantially cancelling the effect of conductance from said electrical output signal.

Claim 21

The servomechanism of claim 1 wherein said transmitting capacitor is a differential capacitor comprising two three-terminal capacitor probes, one of said probes adapted to be mounted in a container to be responsive to the dielectric properties of a material of unknown dielectric properties, and the other of said probes adapted to be mounted in a reference cell including a material of known dielectric properties, and further including means for establishing a temperature equilibrium between the materials of unknown and known dielectric properties.

Claim 22

The servomechanism of claim 20 wherein said second circuit means includes means for substantially cancelling the effect of conductance from said electrical output signal.

Claim 23

The servomechanism of claim 1 wherein said servomechanism is responsive to the dielectric properties of a material flowing in a pipeline; said servomechanism further including a reference dielectric cell adapted to be mounted on such a pipeline, said cell including a first chamber therein for storage of a quantity of material of known dielectric properties, a second chamber at least partially surrounding said first chamber, means for connecting said second chamber into said pipeline so that the material in the pipeline can pass into said second chamber, and from said second chamber back into said pipeline, whereby a temperature equilibrium can be established between the material flowing in the pipeline and said material of known dielectric properties, and a first three-terminal dielectric probe mounted in said first chamber; a second three-terminal dielectric probe adapted to be mounted in said pipeline and spaced from the position where said second cell is connected into said pipeline, said first and second probes comprising a differential transmitting capacitor for said servomechanism; and wherein said receiving capacitor is a differential capacitor; and further including indicating means connected to said control means and responsive thereto to indicate a relationship between dielectric properties of said material in said pipeline and said material of known dielectric properties.

Claim 24

The servomechanism of claim 22 wherein said second circuit means includes means for substantially cancelling the effect of conductance from said electrical output signal.

Claim 25

The servomechanism of claim 1 wherein said servomechanism provides control of the ingredients ratio of two or more materials in a container; and further including a test chamber with a receiving three-terminal capacitor probe mounted therein so that the feed-through capacitance of said receiving probe is responsive to the dielectric properties of said materials when in said chamber, and a reference chamber with a transmitting three-terminal capacitor probe mounted therein so that the feed-through capacitance of said transmitting probe is responsive to the dielectric properties of a reference material of known dielectric properties when in said reference chamber; and wherein said control means further includes valve means connected between a source of at least one of said materials and said container, said valve means responsive to said error signal to permit addition of a quantity of at least one of said materials To said container.

Claim 26

The servomechanism of claim 24 wherein said second circuit means includes means for substantially cancelling the effect of conductance from said electrical output signal.