Standardization of dielectric materials gauges having capacitive probes with remotely controlled balancing circuits using varactors

Claim 3

The system of claim 1 wherein said effective capacitive value changing means includes: a first capacitor having one side coupled to said AC voltage deriving means to be responsive to one of said out-of-phase voltages, a tapped capacitive voltage divider for dividing the said out-of-phase voltages, and means connecting said semiconductor capacitor between the tap of said divider and the other side of said first capacitor.

Claim 4

The system of claim 1 wherein said effective capacitive value changing means comprises an amplifier having a gain less than one, said amplifier being connected to feed AC voltage from said source to said balancing circuit means including said semiconductor capacitor.

Claim 5

The system of claim 3 wherein said amplifier comprises polarity inverting means for providing one of said out-of-phase voltages.

Claim 6

The system of claim 3 wherein said semiconductor capacitor comprises a pair of variable capacitor diodes connected in series back-to-back relation between the output of said amplifier and said probe, and means connecting both said diodes to be back biased by the voltage of said DC source.

Claim 7

The system of claim 1 wherein said semiconductor capacitor comprises a pair of variable capacitor diodes connected back-to-back in a series circuit energized by one of said out-of-phase voltages and coupled to said probe, and means connecting both said diodes to be back biased by the voltage of said DC source.

Claim 8

The system of claim 1 wherein said effective capacitive value changing means comprises means for changing the relative amplitudes of the out-of-phase voltages applied to said probe and balancing circuit means, whereby different amplitude out-of-phase AC voltages are applied to said probe and balancing circuit means.

Claim 9

The sYstem of claim 1 wherein said means for deriving a pair of out-of-phase AC voltages includes phase inverting means comprising a transformer having a grounded center tapped secondary winding, opposite ends of said winding being connected to energize said probe and said balancing circuit means.

Claim 10

The system of claim 8 wherein said probe includes spaced transmitting and receiving electrodes having a grounded shield between them, whereby a relatively fixed capacity is established between said transmitting electrode and shield, said transmitting electrode being connected to be driven by one end of said secondary winding, and a capacitor connected between the other end of said winding an ground, said capacitor having a value approximately equal to said relatively fixed capacity to provide balanced out-of-phase voltage at the opposite ends of said secondary winding.

Claim 11

The system of claim 9 further including a tapped capacitive voltage divider shunting said capacitor connected between said other end of said winding and ground, a further capacitor connected in series circuit with said other end of said winding and said receiving electrode, and means connecting said semiconductor capacitor between the tap of said divider and ground.

Claim 12

A head for monitoring the admittance of a sample responsive to a first AC voltage from a source thereof at a remote location and for feeding an admittance indicating signal to a remote location comprising a first input terminal for a DC voltage source at the remote location, a second input terminal for said AC voltage, means connected to said second input terminal for phase inverting the AC voltage thereby to provide a source of a second AC voltage which is out of phase with said first AC voltage, a capacitive probe including a receiving electrode and a transmitting electrode, a varactor diode including anode and cathode electrodes, means connecting said probe electrodes and said varactor diode electrodes in series circuit with each other and with said AC voltage sources to be driven by said out-of-phase voltages, and means connecting said diode to said first input terminal to be back biased by the DC voltage source, wherein said probe includes a grounded shield electrode between said receiving and transmitting electrodes, whereby the capacity between said receiving and transmitting electrodes is on the order of 1 picofarad and the nominal capacity of said varactor diode is greater than 1 picofarad, and wherein said head includes means for changing the effective capacity of said varactor diode to approximately 1 picofarad.

Claim 13

A head for monitoring the admittance of a sample responsive to a first AC voltage from a source thereof at a remote location and for feeding an admittance indicating signal to a remote location comprising a first input terminal for a DC voltage source at the remote location, a second input terminal for said AC voltage, means connected to said second input terminal for phase inverting the AC voltage thereby to provide a source of a second AC voltage which is out of phase with said first AC voltage, a capacitive probe including a receiving electrode and a transmitting electrode, a varactor diode including anode and cathode electrodes, means connecting said probe electrodes and said varactor diode electrodes in series circuit with each other and with said AC voltage sources to be driven by said out-of-phase voltages, and means connecting said diode to said first input terminal to be back biased by the DC voltage source, wherein said probe includes a grounded shield electrode between said receiving and transmitting electrodes, whereby the capacity between said receiving and transmitting electrodes is on the order of 1 picofarad and the nominal capacity of said varactor diode is greater than 1 picofarad, and wherein said head includes means for changing the effective capacity of said varactor diode to approximately 1 picofarad.

Claim 14

The head of claim 11 wherein said effective capacity value changing means includes: a first capacitor having one side coupled to one of said sources of out-of-phase voltages, a tapped capacitive voltage divider for the out-of-phase voltage provided by said one source, and means connecting said varactor diode between the tap of said divider and the other side of said first capacitor.

Claim 15

The head of claim 11 wherein said effective capacitive changing means includes an amplifier having a gain less than one, said amplifier being connected to feed one of said out-of-phase voltages to said varactor diode.

Claim 16

The head of claim 13 wherein said amplifier comprises said polarity inverting means.

Claim 17

The head of claim 13 further including a second varactor diode, said varactor diodes being connected in series back-to-back relation between the output of said amplifier and said receiving electrode, and means connecting both said diodes to be back biased by the DC voltage at said first input terminal.

Claim 18

The head of claim 11 further including a second varactor diode, said varactor diodes being connected in series back-to-back relation between one of said sources of out-of-phase voltages and said receiving electrode, and means connecting both said diodes to be back biased by the DC voltage at said first input terminal.

Claim 19

The head of claim 11 wherein said effective capaciTive changing means comprises means for changing the relative amplitudes of the out-of-phase voltages applied to said transmitting electrode and one of the electrodes of the varactor.

Claim 20

The head of claim 11 wherein said phase-inverting means comprises a transformer having a grounded center tapped secondary windings, opposite ends of said windings being connected to drive said transmitter electrode and one electrode of said varactor diode.

Claim 21

The head of claim 18 wherein said probe includes a grounded shield between said receiving and transmitting electrodes whereby a relatively fixed capacity is established between said transmitting electrode and shield, said transmitting electrode being connected to be driven by one end of said secondary winding, and a capacitor connected between the other end of said winding and ground, said capacitor having a value approximately equal to said relatively fixed capacity to provide balanced out-of-phase voltages at the opposite ends of said secondary winding.

Claim 22

The head of claim 19 further including a tapped capacitive voltage divider shunting said capacitor connected between said other end of said winding and ground, a further capacitor connected in series circuit with said other end of said winding and said receiving electrode, and means connecting said varactor diode between the tap of said divider and said receiving electrode.

Claim 23

The head of claim 11 further including means for amplifying the AC voltage at said receiving electrode.

Claim 24

In combination with a system for determining a property of a dielectric material at a measuring station including a capacitive probe having spaced electrodes adapted to be placed adjacent said material and electrically coupled thereto, capacitive balancing circuit means, means for energizing said probe and said balancing circuit means with oppositely phased alternating voltages, means coupled to said probe and to said balancing circuit means for producing a signal having a first component dependent on the capacitance of said balancing circuit means and a second component dependent on the capacitance of said probe, and means for relatively displacing said probe from said material to electrically decouple said probe therefrom, the improvement comprising a DC voltage source for producing a DC voltage, a voltage controlled capacitive circuit element included in said balancing circuit means and responsive to said DC voltage to vary the capacitance of the capacitive circuit element in accordance with the value of said DC voltage, circuit means cooperating with said voltage controlled capacitive circuit element for proportioning said second signal component to make its value approximately equal to the value of said first signal component while said probe is electrically decoupled from said material, means for adjusting said DC voltage to a value such that said second signal component is made precisely equal to said first signal component when said probe is relatively displaced from said material to electrically decouple said probe therefrom and for maintaining said adjusted DC voltage value when said probe is again located adjacent to said material, and means utilizing the difference between said first and second signal components while said probe is located adjacent to said material and while said adjusted DC voltage is maintained to determine said material property.

Claim 25

In combination with a system for determining a property of a dielectric material at a measuring station including a capacitive probe having spaced electrodes adapted to be placed adjacent said material and electrically coupled thereto, capacitive balancing circuit means, means for energizing said probe and said balancing circuit means with oppositely phased alternating voltages, means coupled to said probe and to said balancing circuit means for producing a signal having a first component dependent on the capacitance of said balancing circuit means and a second component dependent on the capacitance of said probe, and means for relatively displacing said probe from said material to electrically decouple said probe therefrom, the improvement comprising a DC voltage source for producing a DC voltage, a voltage controlled capacitive circuit element included in said balancing circuit means and responsive to said DC voltage to vary the capacitance of the capacitive circuit element in accordance with the value of said DC voltage, circuit means cooperating with said voltage controlled capacitive circuit element for proportioning said second signal component to make its value approximately equal to the value of said first signal component while said probe is electrically decoupled from said material, means for adjusting said DC voltage to a value such that said second signal component is made precisely equal to said first signal component when said probe is relatively displaced from said material to electrically decouple said probe therefrom and for maintaining said adjusted DC voltage value when said probe is again located adjacent to said material, and means utilizing the difference between said first and second signal components while said probe is located adjacent to said material and while said adjusted DC voltage is maintained to determine said material property.

Claim 28

In combination, a gauge including a probe and a balancing circuit for the probe, said probe being responsive to property variations of a material in an energy field derived from the probe while a measurement of a property of the material is being performed, means for connecting said probe and balancing circuit together and to a voltage source so that an output signal is derived from the gauge indicative of the relative admittances of the probe and balancing circuit, means for adjusting the admittance of the balancing circuit so that a zero voltage is derived from the gauge while a reference material is in said energy field during a balancing operation and a finite, nonzero voltage is derived from the gauge while a sample having characteristics of the property different from the reference material is in said energy field during a measuring operation, said means for adjusting including: means for periodically modulating the admittance of the balancing circuit during the balancing operation whereby the gauge output signal is correspondingly modulated, means for sensing the modulated gauge output signal to derive an indication of the difference between the probe and balancing circuit admittances during the balancing operation, and means responsive to said indication for controlling the average admittance of the balancing circuit so that a zero voltage is derived from the gauge while the admittance is not modulated and the reference material is in the field and for maintaining the admittance of the balancing circuit substantially at the value which resulted in the zero voltage being derived from the gauge during the balancing operation while the measuring operation is being performed.

Claim 29

In combination, a gauge including a probe and a balancing circuit for the probe, said probe being responsive to property variations of a material in an energy field derived from the probe while a measurement of a property of the material is being performed, means for connecting said probe and balancing circuit together and to a voltage source so that an output signal is derived from the gauge indicative of the relative admittances of the probe and balancing circuit, means for adjusting the admittance of the balancing circuit so that a zero voltage is derived from the gauge while a reference material is in said energy field during a balancing operation and a finite, nonzero voltage is derived from the gauge while a sample having characteristics of the property different from the reference material is in said energy field during a measuring operation, said means for adjusting including: means for periodically modulating the admittance of the balancing circuit during the balancing operation whereby the gauge output signal is correspondingly modulated, means for sensing the modulated gauge output signal to derive an indication of the difference between the probe and balancing circuit admittances during the balancing operation, and means responsive to said indication for controlling the average admittance of the balancing circuit so that a zero voltage is derived from the gauge while the admittance is not modulated and the reference material is in the field and for maintaining the admittance of the balancing circuit substantially at the value which resulted in the zero voltage being derived from the gauge during the balancing operation while the measuring operation is being performed.

Claim 30

The combination of claim 24 including a source of reference voltage having the same frequency as the frequency of the modulating means, wherein said sensing means includes a synchronous phase detector responsive to the modulated gauge output signal and said reference voltage.

Claim 31

The combination of claim 25 wherein the balancing circuit includes a voltage-controlled admittance, said modulating means including an AC source connected to control the admittance of said voltage-controlled admittance, said admittance controlling means including: a DC source connected to control the admittance of said voltage-controlled admittance, and means for controlling the magnitude of the DC source in response to said phase detector.

Claim 32

The combination of claim 26 wherein the means for controlling the magnitude of the DC source includes a voltage divider having a tap constituting the output of said DC source, and a DC motor driving said tap said motor being responsive to a DC voltage derived from said phase detector.

Claim 33

The combination of claim 24 wherein said probe balancing circuit includes a pair of back-to-back series connected voltage responsive variable capacitor semiconductor diodes, a network for applying a capacitive voltage control biasing voltage to said diodes to effectively increase the AC impedance of the biasing network to said voltage source.

Claim 34

A gauge circuit for enabling impedance properties of a material to be measured comprising a capacitive probe having first and second electrodes for applying electrostatic energy to the material, a terminal for supplying AC voltage, a balancing circuit connected in shuNt with the electrodes of said probe, a load impedance connected to one electrode of said probe, a phase inverting amplifier connected between said terminal and the other electrode of said probe, said amplifier having a predetermined gain greater than unity, a capacitive voltage divider connected between said terminal and ground, said divider having a tap whereon the amplitude of the AC voltage applied to the terminal is reduced by the reciprocal of the gain of the amplifier, said balancing circuit including capacitive means responsive to the AC voltage derived at said tap and feeding AC current to said load impedance in phase opposition to the AC current fed to the load by the probe and amplifier.

Claim 35

A gauge circuit for enabling impedance properties of a material to be measured comprising a capacitive probe having first and second electrodes for applying electrostatic energy to the material, a terminal for supplying AC voltage, a balancing circuit connected in shuNt with the electrodes of said probe, a load impedance connected to one electrode of said probe, a phase inverting amplifier connected between said terminal and the other electrode of said probe, said amplifier having a predetermined gain greater than unity, a capacitive voltage divider connected between said terminal and ground, said divider having a tap whereon the amplitude of the AC voltage applied to the terminal is reduced by the reciprocal of the gain of the amplifier, said balancing circuit including capacitive means responsive to the AC voltage derived at said tap and feeding AC current to said load impedance in phase opposition to the AC current fed to the load by the probe and amplifier.

Claim 36

The circuit of claim 29 wherein said balancing circuit includes a first capacitor connected in parallel with a voltage-controlled capacitor, said first capacitor having a value substantially equal to but slightly less than the capacitance between said electrodes while only air is in the field between the electrodes, and means for applying a DC voltage to the voltage controlled capacitor to enable the AC voltage across the load to be substantially zero while only air is in the field between the electrodes.

Claim 37

The circuit of claim 30 wherein said voltage-controlled capacitor comprises a pair of back-to-back diodes, said diodes being voltage-controlled variable capacitances.

Claim 38

The circuit of claim 31 further including means for applying a biasing voltage to a common terminal of said diodes, said biasing applying means including a resistive voltage divider having a tap and one terminal connected to the tap of the capacitive voltage divider, another terminal of the resistive voltage divider being responsive to a terminal adapted to be connected to a voltage source controlling the capacitance of the diodes, capacitor means shunting said last named terminal to ground to provide substantially a short circuit for frequencies of the AC source and substantially an open circuit for frequencies of the controlling voltage source, and a resistor connected between the tap of the resistive voltage divider and a common terminal of said diodes.

Claim 39

The circuit of claim 32 wherein the impedances of said resistive voltage divider between the tap thereof and each of the terminals thereof are approximately equal.

Claim 40

The circuit of claim 33 further including another resistive voltage divider in shunt with the capacitive voltage divider and having a tap short circuited to the tap of the capacitive voltage divider, the impedances of the elements of the another resistive voltage divider being in the same proportion as the impedances of the elements of the capacitive voltage divider.

Claim 43

The system of claim 35 wherein said means for balancing includes means for cyclically modulating an impedance of the gauge at a predetermined frequency displaced from both frequencies of said source, and said means for adjusting includes: means for deriving a difference signal indicative of the difference between the relative amplitudes of said first and second signals, and means for chopping the difference signal at said predetermined frequency; a synchronous phase detector, programmer means for sequentially feeding to the phase detector (a) the chopped difference signal and (b) said one of said signals while the impedance of the gauge is being modulated.

Claim 44

The system of claim 36 further including a DC motor means responsive to the phase detector for varying the relative amplitude of the voltages at said frequencies applied by said source to said probe while the chopped difference signal is being fed to the phase detector and for varying the average value of the gauge impedance while the impedance of the gauges is being modulated.

Claim 49

In combination with a system for determining an admittance property of a material at a measuring station including a probe for coupling a field to said material, balancing circuit means connected in shunt with said probe, means for energizing said probe and said balancing circuit means with oppositely phased alternating voltages, means coupled to said probe and to said balancing circuit means for deriving a signal having a first component indicative of the admittance of said balancing circuit means and a second component indicative of the admittance of said probe, a voltage controlled impedance element included in said balancing circuit means, a control voltage source having a frequency displaced from the frequency of the means energizing the probe anD balancing circuit and controlling the impedance of the voltage-controlled impedance, means for adjusting the value of the voltage-controlled impedance in response to the control voltage source for proportioning said second signal component to make the value thereof approximately equal to the value of said first said signal component while said probe is loaded only with a standard material, means for maintaining the value of the voltage-controlled impedance at the value achieved while the standard material is in the field of the probe, and means responsive to the difference between said first and second signal components while a material to be monitored for admittance variations is in the field of the probe.

Claim 50

In combination with a system for determining an admittance property of a material at a measuring station including a probe for coupling a field to said material, balancing circuit means connected in shunt with said probe, means for energizing said probe and said balancing circuit means with oppositely phased alternating voltages, means coupled to said probe and to said balancing circuit means for deriving a signal having a first component indicative of the admittance of said balancing circuit means and a second component indicative of the admittance of said probe, a voltage controlled impedance element included in said balancing circuit means, a control voltage source having a frequency displaced from the frequency of the means energizing the probe anD balancing circuit and controlling the impedance of the voltage-controlled impedance, means for adjusting the value of the voltage-controlled impedance in response to the control voltage source for proportioning said second signal component to make the value thereof approximately equal to the value of said first said signal component while said probe is loaded only with a standard material, means for maintaining the value of the voltage-controlled impedance at the value achieved while the standard material is in the field of the probe, and means responsive to the difference between said first and second signal components while a material to be monitored for admittance variations is in the field of the probe.