Microsensors Corp.

John S Piso

James K Roberge

David M Geary

Measurements of yarn denier using capacitance transducers are automatically corrected for moisture. Samples of the yarn to be run are tested at different moisture levels at different frequencies in each of two capacitance transducers. The difference in the apparent denier outputs of the two transducers has been found to be proportional to moisture content. The difference is added to one of the measured values to provide a more correct reading. The difference may be further corrected by a factor derived from the slopes of the curves of transducer output vs. moisture and the slope of the curve of skein denier vs. moisture.

Moisture corrected denier measurement

The amount of electrically conductive finish that has been applied to a filament is determined by measuring the conductance of a length of the filament. The measurements are made independently of any difference in conductivity of finish mediums by means of a reference cell containing a sample of the particular finish medium used. An electric measurement circuit provides an indication of the amount of finish medium on the filament by determining the ratio of the conductance of the length of filament to the conductance of the reference cell. In one circuit embodiment, two operational amplifiers are placed in series. The reference cell takes the place of the feedback resistor of one operational amplifier and the length of filament takes the place of the input resistance of the other amplifier. The resulting output of the series circuit is a scaled ratio of the conductances of the finish along the length of filament and in the cell. In another circuit embodiment, voltages applied through the length of filament and reference cell are selectively switched into a dual slope integrating circuit. In its preferred form, the finish measuring apparatus is a hand-held device having contacts which may be connected to a filament using a trigger mechanism.

Finish measuring method and apparatus

In a device for continuously monitoring the characteristics of a moving filament, such as the denier of an extended synthetic yarn, by passing the filament through a capacitive sensor to develop an electrical signal representing an absolute measurement of the filament with reference to a prescribed datum, the problem of measurement signal drift arising from contamination of the capacitive sensor is obviated by developing compensating signals to be combined with the filament measurement signal. The compensating signals are digitally formed and stored, thereby eliminating drift in the compensating signals themselves. The compensating signals are developed in an auto-calibration circuit, including an auto-zero circuit and an auto-gain circuit, which receives the measurement signal from the capacitive sensor. While the sensor is vacant, the auto-zero circuit digitally counts clock pulses to generate a digital output, converts the digital output into an analog signal varying with the digital count, detects a prescribed comparison between the analog signal and the input measurement signal, and stops the clock pulse count at a zero compensating value when the comparison is detected. Then, the auto-gain circuit applies an unbalanced drive to the sensor, digitally counts clock pulses to generate a digital output, and varies the measurement signal gain with the digital output. The circuit detects a prescribed comparison between the gain-adjusted measurement signal and a standardized output signal, and stops the clock pulse count at a gain compensating value when the prescribed comparison is detected.

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Framingham, MA, United States of America

John S Piso