Capacitive measuring system with automatic calibration

In apparatus for continuously monitoring a characteristic of a moving elongate filament wherein the filament is passed through a capacitive sensor having means to produce a sensor signal responsive to changes in the capacitance of said sensor, and wherein the zero datum level of said sensor signal may vary with time so as to tend to introduce errors into the accuracy of the measurement;

• the improvement which comprises:
• (A) compensating means for developing a zero-compensating signal and for combining it with said sensor signal so as to produce a composite measurement signal;
• and
• (B) zeroizing-control means normally inoperative while said monitoring apparatus is functioning but controllably activatable to establish the zero level of said composite measurement signal at said zero-datum level;
• said zeroizing-control means including:
• (1) a signal-setting circuit to set the value of said zero-compensating signal to a predetermined level which, when said filament is temporarily removed from said sensor, results in a composite measurement signal substantially offset from said zero-datum level;
• (2) a signal-varying circuit operable to vary said zero-compensating signal through a range of values from said predetermined level and moving in a direction which alters said composite measurement signal towards said zero-datum level;
• (3) a comparator device responsive to said composite measurement signal and operable to produce an output signal indicating when said composite measurement signal has reached said zero-datum level;
• (4) means responsive to said comparator signal for stopping the variation of said zero-compensating signal at the particular value which resulted in a signal at said zero-datum level;
• and
• (5) a memory device for maintaining said zero-compensating signal at said particular value after said zeroizing-control means has been deactivated and said apparatus has resumed normal operation monitoring the characteristic of said moving filament.

In a device for continuously monitoring the characteristics of a moving filament through a capacitive sensor and developing an electrical analog signal to represent an absolute measurement of the filament with reference to a prescribed datum or zero point, the improvement which comprises an automatic zeroizing circuit operable when the filament is removed and including:

• a clock pulse oscillator for generating a train of clock pulses;
• means for activating said clock pulse oscillator;
• a digital counter driven by pulses from said oscillator for generating a digital output signal representing the accumulated count of said clock pulses;
• a digital-to-analog converter coupled to said counter for providing a compensating analog output signal which varies with said digital output signal of said digital counter;
• a zero reference circuit defining the zero point to which the output of said automatic zeroizing circuit is to be referred;
• an adder for adding the analog signal from the capacitive sensor to said compensating analog signal;
• and
• a comparator for comparing the output of said adder to the said zero point of said zero reference circuit and generating a signal to stop the oscillator from generating any further clock pulses when the output values are equivalent;
• whereby when said oscillator stops, said counter maintains its digital count and said compensating analog signal continues to be applied to said adder at a value at which it compensates for drift signal in the capacitive sensor when the filament is removed.

In a device for continuously monitoring the characteristics of a moving filament by passing the filament through a capacitive sensor and developing an electric filament measurement signal to represent an absolute measurement of the filament with reference to a prescribed datum or zero point, the improvement which comprises:

• means for removing said filament from said capacitive sensor;
• means for developing a digital compensating signal reflecting the output of said capacitive sensor when said filament is removed from said capacitive sensor and for storing said digital compensating signal in a digital signal storage device;
• and
• means for combining said filament measurement signal with said digital compensating signal to produce a composite signal compensated for measurement signal drift arising from variations in the capacitive sensor, the storage of said digital zero compensating signal in said digital signal storage device eliminating drift in said zero compensating signal.

In a method for continuously monitoring the characteristics of a moving filament by passing the filament through a capacitive sensor and developing an electrical filament measurement signal to represent an absolute measurement of the filament with reference to a prescribed datum or zero point, the improvement which comprises:

• removing said filament from said capacitive sensor;
• while said filament is removed, developing a digital compensating signal reflecting the output of said capacitive sensor and storing said digital compensating signal in a digital signal storage device;
• returning said filament to said capacitive sensor;
• and
• combining said filament measurement signal with said digital compensating signal to produce a composite signal compensated for measurement signal drift arising from variations in the capacitive sensor, the storage of said digital compensating signal in said digital signal storage device eliminating drift in said compensating signal.

In a device for continuously monitoring the characteristics of a moving filament by passing the filament through a capacitive sensor and developing an electric filament measurement signal to represent an absolute measurement of the filament with reference to a prescribed datum or zero point, the improvement which comprises:

• means for simulating in said capacitive sensor a predetermined filament characteristic;
• means for developing and storing in a digital signal storage device a digital gain compensating signal reflecting the necessary gain to be applied to said measurement signal to provide a predetermined signal;
• and
• means for combining said filament measurement signal with said digitally stored gain compensating signal to produce a signal compensated for gain drift arising from variations in the capacitive sensor, the storage of said digital gain compensating signal in said digital signal storage device eliminating drift in said gain compensating signal.

In apparatus for continuously monitoring a characteristic of a moving elongate filament wherein the filament is passed through a capacitive sensor having means to produce a sensor signal responsive to changes in the capacitance of said sensor, and wherein the gain of said sensor signal may vary with time so as to tend to introduce errors into the accuracy of the measurement;

• the improvement which comprises:
• (A) compensating means for developing a gain-compensating signal and for combining it with said sensor signal so as to produce a composite measurement signal;
• and
• (B) control means normally inoperative while said monitoring apparatus is functioning but controllably activatable to establish the gain of said composite measurement signal at a predetermined level;
• said control means including;
• (1) a signal-setting circuit to set the value of said gain-compensating signal to an offset level which, when said filament is temporarily removed from said sensor and a predetermined characteristic is simulated, results in a composite measurement signal substantially offset from said predetermined level;
• (2) a signal-varying circuit operable to vary said gain-compensating signal through a range of values from said offset level and moving in a direction which alters said composite measurement signal towards said predetermined level;
• (3) a comparator device responsive to said composite measurement signal and operable to produce an output signal indicating when said composite measurement signal has reached said predetermined level;
• (4) means responsive to said comparator signal for stopping the variation of said gain-compensating signal at the particular value which resulted in a signal at said predetermined level;
• and
• (5) a memory device for maintaining said gain-compensating signal at said particular value after said control means has been deactivated and said apparatus has resumed normal operation monitoring the characteristic of said moving filament.

In a method for continuously monitoring the characteristics of a moving filament by passing the filament through a capacitive sensor and developing an electric filament measurement signal to represent an absolute measurement of the filament with reference to a prescribed datum or zero point, the improvement which comprises:

• simulating in said capacitive sensor a predetermined filament characteristic;
• while simulating said filament characteristic, developing and storing in a digital signal storage device a digital gain compensating signal reflecting the necessary gain to be applied to said measurement signal to provide a predetermined signal;
• ending said filament characteristic simulation;
• combining said filament measurement signal with said digitally stored gain compensating signal to produce a signal compensated for gain drift arising from variations in the capacitive sensor the storage of said digital gain compensating signal in said digital signal storage device eliminating drift in said gain compensating signal.

In a device for continuously monitoring the characteristics of a moving filament by passing the filament through a capacitive sensor and developing an electric filament measurement signal to represent an absolute measurement of the filament with reference to a prescribed datum or zero point, the improvement which comprises:

• means for controlling respective auto-zero and auto-gain sequences when said filament is removed from said capacitive sensor;
• means for developing during said auto-zero sequence a digital zero compensating signal reflecting the output of said capacitive sensor when said filament is removed and for storing said digital zero compensating signal in a digital signal storage device;
• means for simulating in said capacitive sensor during said auto-gain sequence a predetermined filament characteristic;
• means for developing and storing in a digital signal storage device a digital gain compensating signal reflecting the necessary gain to be applied to said measurement signal to provide a predetermined signal;
• and
• means for combining said filament measurement signal with said digitally stored zero compensating signal and said digitally stored gain compensating signal to produce a signal compensated for both zero drift and gain drift arising from variations in the capacitive sensor, the digital storage of said compensating signals eliminating drift in said compensating signals.

In a method for continuously monitoring the characteristics of a moving filament by passing the filament through a capacitive sensor and developing an electric filament measurement signal to represent an absolute measurement of the filament with reference to a prescribed datum or zero point, the improvement which comprises:

• removing said filament from said capacitive sensor;
• while said filament is removed, developing a digital zero compensating signal reflecting the output of said capacitive sensor and storing said digital zero compensating signal in a digital signal storage device;
• simulating in said capacitive sensor a predetermined filament characteristic;
• developing and storing in a digital signal storage device a digital gain compensating signal reflecting the necessary gain to be applied to said measurement signal to provide a predetermined signal;
• removing said filament characteristic simulation and returning said filament to said capacitive sensor;
• and
• combining said filament measurement signal with said digitally stored zero compensating signal and said digitally stored gain compensating signal to produce a signal compensated for both zero drift and gain drift arising from variations in the capacitive sensor, the digital storage of said compensating signals eliminating drift in said compensating signals.

In a method for continuously monitoring the characteristics of a moving filament by passing the filament through a capacitive sensor and developing an electric filament measurement signal to represent an absolute measurement of the filament with reference to a prescribed datum or zero point, the improvement which comprises:

• simulating in said capacitive sensor a predetermined filament characteristic;
• while simulating said filament characteristic developing and storing in a memory device a gain compensating signal reflecting the necessary gain to be applied to said measurement signal to provide a predetermined signal;
• ending said filament characteristic simulation;
• and
• controlling said filament measurement signal in accordance with said stored gain compensating signal to produce a signal compensated for gain drift arising from variations in the capacitive sensor, the storage of said gain compensating signal in said memory device eliminating drift in said gain compensating signal.