Apparatus and method for monitoring the status of a radio frequency thickness gauge

Claim 2

In an apparatus for measuring the thickness of an article formed from a dielectric material wherein an antenna is used to establish a radio frequency field outwardly in the direction of an article positioned adjacent thereto; a probe is positioned in said field adjacent to said article; the voltage induced in said probe is an index of the thickness of that portion of said article immediately in front of said probe; a compensated reference voltage is generated during periods when no article is present and held as a constant voltage during periods when an article is present; said induced voltage and said compensated reference voltage are compared to provide a reject signal when the thickness of said article is below a pre-selected value; and said reject signal is transmitted to a reject control mechanism for rejecting articles exhibiting a signal level below a preselected level, the improvement in said apparatus which comprises, in combination: a. a first voltage source for supplying a constant voltage; b. a first voltage comparison means connected to said first voltage source and said compensated reference voltage for generating an output signal when said compensated reference voltage rises above a maximum pre-selected level; c. a first out-of-tolerance alarm means connected to the output of said first voltage comparison means for signaling the rise of said compensated reference voltage above said maximum preselected level in response to said output signal from said first voltage comparison means; d. a second voltage comparison means connected to said first voltage source and said compensated reference voltage for generating an outpuT signal when said compensated reference voltage falls below a minimum pre-selected level; and e. a second out-of-tolerance alarm means connected to the output of said second voltage comparison means for signaling the fall of said compensated reference voltage below said minimum preselected level in response to said output signal from said second voltage comparison means.

Claim 3

The improvement of claim 1, further including control means interposed said reject signal and said reject control mechanism, and connected to the output of said first and said second voltage comparison means, for blocking the passage of said reject signal to said reject control mechanism in response to an output signal from either said first voltage comparison means or said second voltage comparison means.

Claim 4

The improvement of claim 1, wherein said first voltage comparison means comprises, in combination: a. an operational amplifier having at least two input terminals and one output terminal, said operational amplifier being so biased as to give either a first discrete output voltage or a second discrete output voltage as a function of the input to said operational amplifier; b. a first input resistor connected to said compensated reference voltage; c. a second input resistor connected to said first constant voltage supply and connected in parallel with said first input resistor, the common output of said first and second input resistors being connected to one input of said operational amplifier, the relative values of said first and second input resistors being such that a voltage divider is formed which will cause said operational amplifier to present said first discrete output voltage when said compensated reference voltage is below said pre-selected maximum value and to present said second discrete output voltage when said compensated reference voltage is above said pre-selected maximum value; and d. means for blocking the transmission of said first discrete output voltage to said first out-of-tolerance alarm means.

Claim 5

The improvement of claim 1, further including a second constant voltage supply, and wherein said first out-of-tolerance alarm means comprises, in combination: a. an SCR having its cathode connected to ground and its gate connected to the output of said first voltage comparison means; b. a warning light connected in series with the anode of said SCR and said second voltage supply, whereby said light will be off so long as no signal is supplied to the gate of said SCR; and c. a gate circuit for said SCR comprising a resistor and a capacitor connected in parallel with each other, and connected to the gate of said SCR and to ground.

Claim 6

The improvement of claim 1, wherein said second voltage comparison means comprises, in combination: a. an operational amplifier having at least two input terminals and one output terminal, said operational amplifier being so biased as to give either a first discrete output voltage or a second discrete output voltage as a function of the input to said operational amplifier; b. a first input resistor connected to said compensated reference voltage; c. a second input resistor connected to said first constant voltage supply and connected in parallel with said first input resistor, the common output of said first and second input resistors being connected to one input of said operational amplifier, the relative values of said first and second input resistors being such that a voltage divider is formed which will cause said operational amplifier to present said first discrete output voltage when said compensated reference voltage is above said pre-selected minimum value and to present said second discrete output voltage when said compensated reject reference voltage is below said pre-selected minimum value; and d. means for blocking the transmission of said first discrete output voltage to said second out-of-tolerance alarm means.

Claim 7

The improvement of claim 1, further inCluding a second constant voltage supply, and wherein said second out-of-tolerance alarm means comprises, in combination: a. an SCR having its cathode connected to ground and its gate connected to the output of said second voltage comparison means; b. a warning light connected in series with the anode of said SCR and said second voltage supply, whereby said light will be off so long as no signal is supplied to the gate of said SCR; and c. a gate circuit for said SCR comprising a resistor and a capacitor connected in parallel with each other, and connected to the gate of said SCR and to ground.

Claim 8

The improvement of claim 1, wherein said first voltage comparison means comprises, in combination: a. an operational amplifier having at least two input terminals and one output terminal, said operational amplifier being so biased as to give either a first discrete output voltage or a second discrete output voltage as a function of the input to said operational amplifier; b. a first input resistor connected to said compensated reference voltage and to one input of said operational amplifier; c. a second input resistor connected to said first constant voltage supply; d. a variable resistor connected in series to said second input resistor and to a second input of said operational amplifier; e. a Zener diode having its cathode connected to ground and its anode connected between said second input resistor and said variable resistor, the value of said Zener diode being substantially equal to a pre-selected maximum allowed value of said compensated reference voltage; f. a third fixed resistor connected between the cathode of said Zener diode and the output of said variable resistor, said variable resistor serving to adjust the voltage present on said third fixed resistor to a value exactly equal to said pre-selected maximum allowed value of said compensated reference voltage, whereby said operational amplifier will present said first discrete output voltage when said compensated reference voltage is below said pre-selected maximum value and said second discrete output voltage when said compensated reference voltage is above said pre-selected maximum value; and g. means for blocking the transmission of said first discrete output voltage to said first out-of-tolerance alarm means.

Claim 9

The improvement of claim 1, wherein said second voltage comparison means comprises, in combination: a. an operational amplifier having at least two input terminals and one output terminal, said operational amplifier being so biased as to give either a first discrete output voltage or a second discrete output voltage as a function of the input to said operational amplifier; b. a first input resistor connected to said compensated reference voltage and to one input of said operational amplifier; c. a second input resistor connected to said first constant voltage supply; d. a variable resistor connected in series to said second input resistor and to a second input of said operational amplifier; e. a Zener diode having its cathode connected to ground and its anode connected between said second input resistor and said variable resistor, the value of said Zener diode being substantially equal to a preselected minimum allowed value of said compensated reject reference voltage; f. a third fixed resistor connected between the cathode of said Zener diode and the output of said variable resistor, said variable resistor serving to adjust the voltage present on said third fixed resistor to a value exactly equal to said pre-selected minimum allowed value of said compensated reference voltage, whereby said operational amplifier will present said first discrete output voltage when said compensated reference voltage is above said pre-selected minimum value and said second discrete output voltage when said compensated reference voltage is below said pre-selected minimum value; and g. means for blocking the tranSmission of said first discrete output voltage to said second out-of-tolerance alarm means.

Claim 10

The apparatus of claim 2, further including a second voltage supply, and wherein said control means comprises, in combination: a. a normally closed relay having at least one contact pair, said reject signal passing through said contact pair to said reject control mechanism; b. an SCR having its cathode connected to ground and its gate connected to the output of both said first and second voltage comparison means; c. an operating coil within said relay connected in series with the anode of said SCR and said second voltage supply for effecting the opening of said contact pair when said operating coil ie energized, whereby said reject signal will be passed to said reject control mechanism so long as no signal is supplied to the gate of said SCR, and said reject control mechanism will be disabled by the opening of said contact pair whenever a signal is furnished to the gate of said SCR by either said first voltage comparison means or said second voltage comparison means; and d. a gate circuit for said SCR comprising a resistor and a capacitor connected in parallel with each other and connected to the gate of said SCR and to ground.

Claim 11

In an apparatus for measuring the thickness of an article formed from a dielectric material wherein an antenna is used to establish a radio frequency field outwardly in the direction of an article positioned adjacent thereto; a probe is positioned in said field adjacent to said article; the voltage induced in said probe is an index of the thickness of that portion of said article immediately in front of said probe; a compensated reference voltage is generated during periods when no article is present and held as a constant voltage during periods when an article is present; said induced voltage and said compensated reference voltage are compared to provide a reject signal when the thickness of said article is below a pre-selected value; and said reject signal is transmitted to a reject control mechanism for rejecting articles exhibiting a signal level below a pre-selected level, the improvement in said apparatus which comprises, in combination: a. circuit means, having an input connected to said compensated reference voltage, for generating, as an output signal, the first derivative with respect to time of said compensated reference voltage; b. a full wave rectifier having its input connected to the output of said circuit means; c. a rate-of-change gate means, having its input connected to the output of said full wave rectifier, for generating a signal when the rate of change of said compensated reference voltage rises above a pre-selected value; and d. a system oscillation warning means, connected to the output of said rate-of-change gate means, for signaling the rise of the rate of change of said compensated reference voltage above said pre-selected value.

Claim 12

In an apparatus for measuring the thickness of an article formed from a dielectric material wherein an antenna is used to establish a radio frequency field outwardly in the direction of an article positioned adjacent thereto; a probe is positioned in said field adjacent to said article; the voltage induced in said probe is an index of the thickness of that portion of said article immediately in front of said probe; a compensated reference voltage is generated during periods when no article is present and held as a constant voltage during periods when an article is present; said induced voltage and said compensated reference voltage are compared to provide a reject signal when the thickness of said article is below a pre-selected value; and said reject signal is transmitted to a reject control mechanism for rejecting articles exhibiting a signal level below a pre-selected level, the improvement in said apparatus which comprises, in combination: a. circuit means, having an input connected to said compensated reference voltage, for generating, as an output signal, the first derivative with respect to time of said compensated reference voltage; b. a full wave rectifier having its input connected to the output of said circuit means; c. a rate-of-change gate means, having its input connected to the output of said full wave rectifier, for generating a signal when the rate of change of said compensated reference voltage rises above a pre-selected value; and d. a system oscillation warning means, connected to the output of said rate-of-change gate means, for signaling the rise of the rate of change of said compensated reference voltage above said pre-selected value.

Claim 13

The improvement of claim 10, wherein said circuit means comprises, in combination: a. an operational amplifier having an output connected to the input of said full wave rectifier; b. a resistor and a capacitor connected in series with one another and with said compensated reference voltage and to an input of said operational amplifier; c. a fixed feedback resistor connected between said input of said operational amplifier and said output of said operational amplifier; and d. a variable feedback resistor connected in series with said fixed feedback resistor for adjusting the maximum allowable rate of change of said compensated reference voltage.

Claim 14

The improvement of claim 10, wherein said rate-of-change gear means comprises, in combination: a. a resistor connected to ground and in parallel with the output of said full wave rectifier; and b. a capacitor connected in parallel with said resistor and connected to ground, the relative values of said resistor and said capacitor being such that so long as the rAte of change of said compensated reference voltage is below said pre-selected value, said resistor will discharge said capacitor before a signal can be propagated to said system oscillation warning means.

Claim 15

The improvement of claim 10, further including a voltage supply, and wherein said system oscillation warning means comprises, in combination: a. an SCR having its cathode connected to ground and its gate connected to the output of said rate-of-change gate means; b. a warning light connected in series with the anode of said SCR and said voltage supply, whereby said light will be off so long as no signal is supplied to the gate of said SCR; and c. a gate circuit for said SCR comprising a resistor and a capacitor connected in parallel with each other and connected to the gate of said SCR and to ground.

Claim 16

The improvement of claim 10, further including control means, interposed said reject signal and said reject control mechanism, and connected to the output of said rate-of-change gate means, for blocking the passage of said reject signal to said reject control mechanism in response to an output signal from said rate-of-change gate means.

Claim 17

The apparatus of claim 14, further including a voltage supply, and wherein said control means comprises, in combination: a. a normally closed relay having at least one contact pair, said reject signal passing through said contact pair to said reject control mechanism; ''b. an SCR having its cathode connected to ground and its gate connected to the output of said rate-of-change gate means; c. an operating coil within said relay connected in series with the anode of said SCR and said voltage supply for effecting the opening of said contact pair when said operating coil is energized, whereby said reject signal will be passed to said reject control mechanism so long as no signal is supplied to the gate of said SCR, and said reject control mechanism will be disabled by the opening of said contact pair whenever a signal is furnished to the gate of said SCR by said rate-of-change gate means; and d. a gate circuit for said SCR comprising a resistor and a capacitor connected in parallel with each other and connected to the gate of said SCR and to ground.

Claim 18

In an apparatus for measuring the thickness of an article formed from a dielectric material, wherein an antenna ia used to establish a radio frequency field outwardly in the direction of an article positioned adjacent thereto; a probe is positioned in said field adjacent to said article; the voltage induced in said probe is an index of the thickness of that portion of said article immediately in front of said probe; a compensated reference voltage is generated during periods when no article is present and held as a constant voltage during periods when an article is present; said induced voltage and said compensated reference voltage are compared to provide a reject signal when the thickness of said article is below a pre-selected value; and said reject signal is transmitted to a reject control mechanism for rejecting articles exhibiting a signal level below a pre-selected level, the improvement in said apparatus which comprises, in combination: a. a first voltage source for supplying a constant voltage; b. a first voltage comparison means connected to said first voltage source and said compensated reference voltage for generating an output signal when said compensated reference voltage rises above a maximum pre-selected level; c. a first out-of-tolerance alarm means connected to the output of said first voltage comparison means for signaling the rise of said compensated reference voltage above said maximum pre-selected level in response to said output signal from said first voltage comparison means; d. a second voltage comparison means connected to said first voltage source and said compensated reference voltage for generating an output signal when said compensated reference voltage falls below a mInimum pre-selected level; e. a second out-of-tolerance alarm means connected to the output of said second voltage comparison means for signaling the fall of said compensated reference voltage below said minimum pre-selected level in response to said output signal from said second voltage comparison means; f. circuit means, having an input connected to said compensated reference voltage, for generating, as an output signal, the first derivative with respect to time of said compensated reference voltage; g. a full wave rectifier having its input connected to the output of said circuit means; h. a rate-of-change gate means, having its input connected to the output of said full wave rectifier, for generating a signal when the rate of change of said compensated reference voltage rises above a pre-selected value; and i. a system oscillation warning means, connected to the output of said rate-of-change gate means, for signaling the rise of the rate of change of said compensated reference voltage above said pre-selected value.

Claim 19

In an apparatus for measuring the thickness of an article formed from a dielectric material, wherein an antenna ia used to establish a radio frequency field outwardly in the direction of an article positioned adjacent thereto; a probe is positioned in said field adjacent to said article; the voltage induced in said probe is an index of the thickness of that portion of said article immediately in front of said probe; a compensated reference voltage is generated during periods when no article is present and held as a constant voltage during periods when an article is present; said induced voltage and said compensated reference voltage are compared to provide a reject signal when the thickness of said article is below a pre-selected value; and said reject signal is transmitted to a reject control mechanism for rejecting articles exhibiting a signal level below a pre-selected level, the improvement in said apparatus which comprises, in combination: a. a first voltage source for supplying a constant voltage; b. a first voltage comparison means connected to said first voltage source and said compensated reference voltage for generating an output signal when said compensated reference voltage rises above a maximum pre-selected level; c. a first out-of-tolerance alarm means connected to the output of said first voltage comparison means for signaling the rise of said compensated reference voltage above said maximum pre-selected level in response to said output signal from said first voltage comparison means; d. a second voltage comparison means connected to said first voltage source and said compensated reference voltage for generating an output signal when said compensated reference voltage falls below a mInimum pre-selected level; e. a second out-of-tolerance alarm means connected to the output of said second voltage comparison means for signaling the fall of said compensated reference voltage below said minimum pre-selected level in response to said output signal from said second voltage comparison means; f. circuit means, having an input connected to said compensated reference voltage, for generating, as an output signal, the first derivative with respect to time of said compensated reference voltage; g. a full wave rectifier having its input connected to the output of said circuit means; h. a rate-of-change gate means, having its input connected to the output of said full wave rectifier, for generating a signal when the rate of change of said compensated reference voltage rises above a pre-selected value; and i. a system oscillation warning means, connected to the output of said rate-of-change gate means, for signaling the rise of the rate of change of said compensated reference voltage above said pre-selected value.

Claim 20

The improvement of claim 16, further including control means, interposed said thickness signal and said reject control mechanism, and connected to the output of said first and said second voltage comparison means and to the output of said rate-of-change gate means, for blocking the passage of said reject signal to said reject control mechanism in response to an output signal from any one of said first voltage comparison means, said second voltage comparison means, or said rate-of-change gate means.

Claim 21

The improvement of claim 16, wherein said first voltage comparison means comprises, in combination: a. an operational amplifier having at least two input terminals and one output terminal, said operational amplifier being so biased as to give either a first discrete output voltage or a second discrete output voltage as a function of the input to said operational amplifier; b. a first input resistor connected to said compensated reference voltage; c. a second input resistor connected to said first constant voltage supply in parallel with said first input resistor, the common output of said first and second input resistors being connected to one input of said operational amplifier, the relative values of said first and second input resistors being such that a voltage divider is formed which will cause said operational amplifier to present said first discrete output voltage when said compensated reference voltage is below said pre-selected maximum value and to present said second discrete output voltage when said compensated reference voltage is above said pre-selected maximum value; and e. means for blocking the transmission of said first discrete output voltage to said first out-of-tolerance alarm means.

Claim 22

The improvement of claim 16, further including a second constant voltage supply, and wherein said first out-of-tolerance alarm means comprises, in combination: a. an SCR having its cathode connected to ground and its gate connected to the output of said first voltage comparison means; b. a warning light connected in series with the anode of said SCR and said second voltage supply, whereby said light will be off so long as no signal is supplied to the gate of said SCR; and c. a gate circuit for said SCR comprising a resistor and a capacitor connected in parallel with each other and connected to the gate of said SCR and to ground.

Claim 23

The improvement of claim 16, wherein said second voltage comparison means comprises, in combination: a. an operational amplifier having at least two input terminals and one output terminal, said operational amplifier being so biased as to give either a first discrete output voltage or a second discrete output voltage as a function of the input to said operational amplifier; b. a first input resistor connected to said compensated reference voltage; c. a second input resistor connected to said first constant voltage supply in parallel with said first input resistor, the common output of said first and second input resistors being connected to one input of said operational amplifier, the relative values of said first and second input resistors being such that a voltage divider is formed which will cause said operational amplifier to present said first discrete output voltage when said compensated reference voltage is above said pre-selected minimum value and to present said second discrete output voltage when said compensated reference voltage is below said pre-selected minimum value; and d. means for blocking the transmission of said first discrete output voltage to said second out-of-tolerance alarm means.

Claim 24

The improvement of claim 1, further including a second constant voltage supply, and wherein said second out-of-tolerance alarm means comprises, in combination: a. an SCR having its cathode connected to ground and its gate connected to the output of said second voltage comparison means; b. a warning light connected in series with the anode of said SCR and said second voltage supply, whereby said light will be off so long as no signal is supplied to the gate of said SCR; and c. a gate circuit for said SCR comprising a resistor and a capacitor connected in parallel with each other, and connected to the gate of said SCR and to ground.

Claim 25

The improvement of claim 16, wherein said first voltage comparison means comprises, in combination: a. an operational amplifier having at least two input terminals and one output terminal, said operational amplifier being so biased as to give either a first discrete output voltage or a second discrete output voltage as a function of the input to said operational amplifier; b. a first input resistor connected to said compensated reference voltage and to one input of said operational amplifier; c. a second input resistor connected to said first constant voltage supply; d. a variable resistor connected in series to said second input resistor and to a second input of said operational amplifier; e. a Zener diode having its cathode connected to ground and its anode connected between said second input resistor and said variable resistor, the value of said Zener diode being substantially equal to pre-selected maximum allowed value of said compensated reject voltage; f. a third fixed resistor connected between the cathode of said Zener diode and the output of said variable resistor, said variable resistor serving to adjust the voltage present on said third fixed resistor to a value exactly equal to said pre-selected maximum allowed value of said compensated reference voltage, whereby said operational amplifier will present said first discrete output voltage when said compensated reference voltage is below said pre-selected maximum value and said second discrete output voltage when said compensated reference voltage is above said pre-selected maximum value; and g. means for blocking the transmission of said first discrete output voltage to said first out-of-tolerance alarm means.

Claim 26

The improvement of claim 16, wherein said second voltage comparison means comprises, in combination: a. an operational amplifier having at least two input terminals and one output terminal, said operational amplifier being so biased as to give either a first discrete output voltage or a second discrete output voltage as a function of the input to said operational amplifier; b. a first input resistor connected to said compensated reference voltage and to one input of said operational amplifier; c. a second input resistor connected to said first constant voltage supply; d. a variable resistor connected in series to said second input resistor and to a second input of said operational amplifier; e. a Zener diode having its cathode connected to ground and its anode connected between said second input resistor and said variable resistor, the value of said Zener diode being substanTially equal to a pre-selected minimum allowed value of said compensated reject reference voltage; f. a third fixed resistor connected between the cathode of said Zener diode and the output of said variable resistor, said variable resistor serving to adjust the voltage present on said third fixed resistor to a value exactly equal to said pre-selected minimum allowed value of said compensated reference voltage, whereby said operational amplifier will present said first discrete output voltage when said compensated reference voltage is above said pre-selected minimum value and said second discrete output voltage when said compensated reference voltage is below said pre-selected minimum value; and g. means for blocking the transmission of said first discrete output voltage to said second out-of-tolerance alarm means.

Claim 27

The improvement of claim 16, wherein said circuit means comprises, in combination: a. an operational amplifier having an output connected to the input of said full wave rectifier; b. a resistor and a capacitor connected in series with one another and with said compensated reference voltage and to an input of said operational amplifier; c. a fixed feedback resistor connected between said input of said operational amplifier and said output of said operational amplifier; and d. a variable feedback resistor connected in series with said fixed feedback resistor for adjusting the maximum allowable rate of change of said compensated reference voltage.

Claim 28

The improvement of claim 16, wherein said rate-of-change gate means comprises, in combination: a. a resistor connected to ground and in parallel with the output of said full wave rectifier; and b. a capacitor connected in parallel with said resistor and connected to ground, the relative values of said resistor and said capacitor being such that so long as the rate of change of said compensated reference voltage is below said pre-selected value, said resistor will discharge said capacitor before a signal can be propagated to said system oscillation warning means.

Claim 29

The improvement of claim 16, further including a second voltage supply, and wherein said system oscillation warning means comprises, in combination: a. an SCR having its cathode connected to ground and its gate connected to the output of said rate-of-change gate means; b. a warning light connected in series with the anode of said SCR and said second voltage supply, whereby said light will be off so long as no signal is supplied to the gate of said SCR; and c. a gate circuit for said SCR comprising a resistor and a capacitor connected in parallel with each other and connected to the gate of said SCR and to ground.

Claim 30

The apparatus of claim 17, further including a second constant voltage supply, and wherein said control means comprises, in combination: a. a normally closed relay having at least one contact pair, said reject signal passing through said contact pair to said reject control mechanism; b. an SCR having its cathode connected to ground and its gate connected to the output of both said first and second voltage comparison means and to the output of said rate-of-change gate means; c. an operating coil within said relay connected in series with the anode of said SCR and said second voltage supply for effecting the opening of said contact pair when said operating coil is energized, whereby said reject signal will be passed to said reject control mechanism so long as no signal is supplied to the gate of said SCR, and said reject control mechanism will be disabled by the opening of said contact pair whenever a signal is furnished to the gate of said SCR by any one of said first voltage comparison means, said second voltage comparison means, or said rate-of-change gate means; and d. a gate circuit for said SCR comprising a resistor and a capacitor connected in parallel with each other and connected to the gate of said SCR and to ground.

Claim 31

In a method for inspecting dielectric articles wherein a radio-frequency field is provided at an inspection station; an attenuated signal of said field is detected as an index of the thickness of an article placed in said field; a compensated reference signal is generated during periods when no article is present in said inspection station and held as a constant value when articles are present in said inspection station; and said attenuated signal and said compensated reference signal are summed to give an output signal which is a measure of the thickness of said article, the improvement in said method which comprises the steps of: a. electronically comparing the value of said compensated reference signal with a fixed signal level; b. electronically generating a first out-of-tolerance signal when the value of said compensated reference signal rises above a pre-selected level; c. signaling the rise of said compensated reference signal above said pre-selected value in response to said first out-of-tolerance signal; d. electronically generating a second out-of-tolerance signal when the value of said compensated reference signal falls below a pre-selected value; and e. signaling the fall of said compensated reference signal below said pre-selected value in response to said second out-of-tolerance signal.

Claim 32

In a method for inspecting dielectric articles wherein a radio-frequency field is provided at an inspection station; an attenuated signal of said field is detected as an index of the thickness of an article placed in said field; a compensated reference signal is generated during periods when no article is present in said inspection station and held as a constant value when articles are present in said inspection station; and said attenuated signal and said compensated reference signal are summed to give an output signal which is a measure of the thickness of said article, the improvement in said method which comprises the steps of: a. electronically comparing the value of said compensated reference signal with a fixed signal level; b. electronically generating a first out-of-tolerance signal when the value of said compensated reference signal rises above a pre-selected level; c. signaling the rise of said compensated reference signal above said pre-selected value in response to said first out-of-tolerance signal; d. electronically generating a second out-of-tolerance signal when the value of said compensated reference signal falls below a pre-selected value; and e. signaling the fall of said compensated reference signal below said pre-selected value in response to said second out-of-tolerance signal.

Claim 33

The method of claim 28, wherein said thickness output signal is compared with a pre-selected minimum thickness level; a reject signal is generated if said thickness output signal is below said minimum level; and said reject signal is transmitted to a reject control mechanism to reject an article whose thickness is below said minimum level, and wherein said improvement further includes the step of: f. blocking the transmission of said reject signal to said reject control mechanism in response to either said first out-of-tolerance signal or said second out-of-tolerance signal.

Claim 34

In a method for inspecting dielectric articles wherein a radio-frequency field is provided at an inspection station; an attenuated signal of said field is detected as an index of the thickness of an article placed in said field; a compensated reference signal is generated during periods when no article is present in said inspection station, and held as a constant value when articles are present in said inspection station; and said attenuated signal and said compensated reference signal are summed to give an output signal which is a measure of the thickness of said article, the improvement in said method which comprises the steps of: a. electronically generating the first derivative with respect to time of said compensated reference voltage, to obtain a signal representing the rate of change of said compensated reference signal; b. electronically comprising said rate-of-change signal of said compensated reference signal with a preselected maximum allowed rate of change of said compensated reference signal; c. electronically generating an oscillation warning signal when said rate of change of said compensated reference signal exceeds said pre-selected maximum allowed rate; and d. signaling the rise of said rate of change of said compensated reference voltage above said pre-selected maximum allowed rate.

Claim 35

In a method for inspecting dielectric articles wherein a radio-frequency field is provided at an inspection station; an attenuated signal of said field is detected as an index of the thickness of an article placed in said field; a compensated reference signal is generated during periods when no article is present in said inspection station, and held as a constant value when articles are present in said inspection station; and said attenuated signal and said compensated reference signal are summed to give an output signal which is a measure of the thickness of said article, the improvement in said method which comprises the steps of: a. electronically generating the first derivative with respect to time of said compensated reference voltage, to obtain a signal representing the rate of change of said compensated reference signal; b. electronically comprising said rate-of-change signal of said compensated reference signal with a preselected maximum allowed rate of change of said compensated reference signal; c. electronically generating an oscillation warning signal when said rate of change of said compensated reference signal exceeds said pre-selected maximum allowed rate; and d. signaling the rise of said rate of change of said compensated reference voltage above said pre-selected maximum allowed rate.

Claim 36

The method of claim 30, wherein said thickness output signal is compared with a pre-selected minimum thickness level; a reject signal is generated if said thickness output signal is below said minimum level; and said reject signal is transmitted to a reject control mechanism to reject an article whose thickness is below said minimum level, and wherein said improvement further includes the step of: e. blocking the transmission of said reject signal to said reject control mechanism in response to said oscillation warning signal.

Claim 37

In a method for inspecting dielectric articles wherein a radio-frequency field is provided at an inspection station; an attenuated signal of said field is detected as an index of the thickness Of an article placed in said field; a compensated reference signal is generated during periods when no article is present in said inspection station and held as a constant value when articles are present in said inspection station; and said attenuated signal and said compensated reference signal are summed to give an output signal which is a measure of the thickness of said article, the improvement in said method which comprises the steps of: a. electronically comparing the value of said compensated reference signal with a fixed signal level; b. electronically generating a first out-of-tolerance signal when the value of said compensated reference signal rises above a pre-selected level; c. signaling the rise of said compensated reference signal above said pre-selected value in response to said first out-of-tolerance signal; d. electronically generating a second out-of-tolerance signal when the value of said compensated reference signal falls below a pre-selected value; e. signaling the fall of said compensated reference signal below said pre-selected value in response to said second out-of-tolerance signal; f. electronically generating the first derivative with respect to time of said compensated reference voltage to obtain a signal representing the rate of change of said compensated reference signal; g. electronically comparing said rate-of-change signal of said compensated reference signal with a preselected maximum allowed rate of change of said compensated reference signal; h. electronically generating an oscillation warning signal when said rate of change of said compensated reference signal exceeds said pre-selected maximum allowed rate; and i. signaling the rise of said rate of change of said compensated reference voltage above said pre-selected maximum allowed rate.

Claim 38

In a method for inspecting dielectric articles wherein a radio-frequency field is provided at an inspection station; an attenuated signal of said field is detected as an index of the thickness Of an article placed in said field; a compensated reference signal is generated during periods when no article is present in said inspection station and held as a constant value when articles are present in said inspection station; and said attenuated signal and said compensated reference signal are summed to give an output signal which is a measure of the thickness of said article, the improvement in said method which comprises the steps of: a. electronically comparing the value of said compensated reference signal with a fixed signal level; b. electronically generating a first out-of-tolerance signal when the value of said compensated reference signal rises above a pre-selected level; c. signaling the rise of said compensated reference signal above said pre-selected value in response to said first out-of-tolerance signal; d. electronically generating a second out-of-tolerance signal when the value of said compensated reference signal falls below a pre-selected value; e. signaling the fall of said compensated reference signal below said pre-selected value in response to said second out-of-tolerance signal; f. electronically generating the first derivative with respect to time of said compensated reference voltage to obtain a signal representing the rate of change of said compensated reference signal; g. electronically comparing said rate-of-change signal of said compensated reference signal with a preselected maximum allowed rate of change of said compensated reference signal; h. electronically generating an oscillation warning signal when said rate of change of said compensated reference signal exceeds said pre-selected maximum allowed rate; and i. signaling the rise of said rate of change of said compensated reference voltage above said pre-selected maximum allowed rate.

Claim 39

The method of claim 32, wherein said thickness output signal is compared with a pre-selected minimum thickness level; a reject signal is generated if said thickness output signal is below said minimum level; and said reject signal is transmitted to a reject control mechanism to reject an article whose thickness is below said minimum level, and wherein said improvement further includes the step of: j. blocking the transmission of said reject signal to said reject control mechanism in response to any one of said first out-of-tolerance signal, said second out-of-tolerance signal or said oscillation warning signal.

Claim 40

In a method for sorting dielectric articles as a function of their thickness, wherein a radio-frequency field is provided at an inspection station; an attenuated signal of said field is detected as an index of the thickness of an article placed in said field; a compensated reference signal is generated, during periods when no article is present in said inspection station, and held as a constant value when articles are present in said inspection station; said attenuated signal and said compensated reference signal are summed to give an output signal which is a measure of the thickness of said article; said thickness output signal is compared with a pre-selected minimum thickness level; a reject signal is generated if said thickness output signal is below said minimum level; and said reject signal is transmitted to a reject control mechanism to reject an article whose thickness is below said minimum level, the improvement in said method which comprises the steps of: a. electronically comparing the value of said compensated reference signal with a fixed signal level; b. electronically generating a first out-of-tolerance signal when the value of said compensated reference signal rises above a pre-selected level; c. electronically generating a second out-of-tolerance signal when the value of said compensated reference signal falls below a pre-selected value; and d. blocking the transmission of said reject signal to said reject control mechanism in reponse to either said first out-of-tolerance signal or said second out-of-tolerance signal.

Claim 41

In a method for sorting dielectric articles as a function of their thickness, wherein a radio-frequency field is provided at an inspection station; an attenuated signal of said field is detected as an index of the thickness of an article placed in said field; a compensated reference signal is generated, during periods when no article is present in said inspection station, and held as a constant value when articles are present in said inspection station; said attenuated signal and said compensated reference signal are summed to give an output signal which is a measure of the thickness of said article; said thickness output signal is compared with a pre-selected minimum thickness level; a reject signal is generated if said thickness output signal is below said minimum level; and said reject signal is transmitted to a reject control mechanism to reject an article whose thickness is below said minimum level, the improvement in said method which comprises the steps of: a. electronically comparing the value of said compensated reference signal with a fixed signal level; b. electronically generating a first out-of-tolerance signal when the value of said compensated reference signal rises above a pre-selected level; c. electronically generating a second out-of-tolerance signal when the value of said compensated reference signal falls below a pre-selected value; and d. blocking the transmission of said reject signal to said reject control mechanism in reponse to either said first out-of-tolerance signal or said second out-of-tolerance signal.

Claim 42

In a method for sorting dielectric articles as a function of their thickness, wherein a radio-frequency field is provided at an inspection station; an attenuated signal of said field is detected as an index of the thickness of an article placed in said field; a compensated reference signal is generated, during periods when no article is present in said inspection station, and held as a constant value when articles are present in said inspection station; said attenuated signal and said compensated reference signal are summed to give an output signal which is a measure of the thickness of said article; said thickness output signal is compared with a pre-selected minimum thickness level; a reject signal is generated if said thickness output signal is below said minimum level; and said reject signal is transmitted to a reject control mechanism to reject an article whose thickness is below said minimum level, the improvement in said method which comprises the steps of: a. electronically generating the first derivative with respect to time of said compensated reference voltage, to obtain a signal representing the rate of change of said compensated reference signal; b. electronicially comparing said rate-of-change signal of said compensated reference signal with a preselected maximum allowed rate of change of said compensated reference signal; c. electronically generating an oscillation warning signal when said rate of change of said compensated reference signal exceeds said pre-selected maximum allowed rate; and d. blocking the transmission of said reject signal to said reject control mechanism in respone to said oscillation warning signal.

Claim 43

In a method for sorting dielectric articles as a function of their thickness, wherein a radio-frequency field is provided at an inspection station; an attenuated signal of said field is detected as an index of the thickness of an article placed in said field; a compensated reference signal is generated, during periods when no article is present in said inspection station, and held as a constant value when articles are present in said inspection station; said attenuated signal and said compensated reference signal are summed to give an output signal which is a measure of the thickness of said article; said thickness output signal is compared with a pre-selected minimum thickness level; a reject signal is generated if said thickness output signal is below said minimum level; and said reject signal is transmitted to a reject control mechanism to reject an article whose thickness is below said minimum level, the improvement in said method which comprises the steps of: a. electronically generating the first derivative with respect to time of said compensated reference voltage, to obtain a signal representing the rate of change of said compensated reference signal; b. electronicially comparing said rate-of-change signal of said compensated reference signal with a preselected maximum allowed rate of change of said compensated reference signal; c. electronically generating an oscillation warning signal when said rate of change of said compensated reference signal exceeds said pre-selected maximum allowed rate; and d. blocking the transmission of said reject signal to said reject control mechanism in respone to said oscillation warning signal.

Claim 44

In a method for sorting dielectric articles as a function of their thickness, wherein a radio-frequency field is provided at an inspection station; an attenuated signal of said field is detected as an index of the thickness of an article placed in said field; a compensated reference signal is generated, during periods when no article is present in said inspection station, and held as a constant value when articles are present in said inspection station; said attenuated signal and said compensated reference signal are summed to give an output signal which is a measure of the thickness of said article; said thickness output signal is compared with a pre-selected minimum thickness level; a reject signal is generated if said thickness output signal is below said minimum level; and said reject signal is transmitted to a reject control mechanism to reject an article whose thickness is below said minimum level, the improvement in said method which comprises the steps of: a. electronically comparing the value of said compensated reference signal with a fixed signal level; b. electronicially generating a first out-of-tolerance signal when the value of said compensated reference signal rises above a pre-selected level; c. electronicially generating a second out-of-tolerance signal when the value of said compensated reference signal falls below a pre-selected value; d. electronically generating the first derivative with respect to time of said compensated reference voltage to obtain a signal representing the rate of change of said compensated reference signal. e. electronically comparing said rate-of-change signal of said compensated reference signal with a preselected maximum allowed rate of change of said compensated reference signal; f. electronically generating an oscillation warning signal when said rate of change of said compensated reference signal exceeds said pre-selected maximum allowed rate; and g. blocking the transmission of said reject signal to said reject control mechanism in response to any one of said first out-of-tolerance signal, said second out-of-tolerance signal or said oscillation warning signal.

Claim 45

In a method for sorting dielectric articles as a function of their thickness, wherein a radio-frequency field is provided at an inspection station; an attenuated signal of said field is detected as an index of the thickness of an article placed in said field; a compensated reference signal is generated, during periods when no article is present in said inspection station, and held as a constant value when articles are present in said inspection station; said attenuated signal and said compensated reference signal are summed to give an output signal which is a measure of the thickness of said article; said thickness output signal is compared with a pre-selected minimum thickness level; a reject signal is generated if said thickness output signal is below said minimum level; and said reject signal is transmitted to a reject control mechanism to reject an article whose thickness is below said minimum level, the improvement in said method which comprises the steps of: a. electronically comparing the value of said compensated reference signal with a fixed signal level; b. electronicially generating a first out-of-tolerance signal when the value of said compensated reference signal rises above a pre-selected level; c. electronicially generating a second out-of-tolerance signal when the value of said compensated reference signal falls below a pre-selected value; d. electronically generating the first derivative with respect to time of said compensated reference voltage to obtain a signal representing the rate of change of said compensated reference signal. e. electronically comparing said rate-of-change signal of said compensated reference signal with a preselected maximum allowed rate of change of said compensated reference signal; f. electronically generating an oscillation warning signal when said rate of change of said compensated reference signal exceeds said pre-selected maximum allowed rate; and g. blocking the transmission of said reject signal to said reject control mechanism in response to any one of said first out-of-tolerance signal, said second out-of-tolerance signal or said oscillation warning signal.