Abstract: Denier and other optically transmissivity-dependent parameters of yarn are monitored on-line and in real-time with a preferably microprocessor-controlled high frequency modulated-demodulated optically-based system. An LED is spaced-apart from an array of preferably identical photodetector ("PD") diodes that will track one another, with the yarn spaced between one of the PDs. The LED outputs preferably collimated light in response to a periodic LED drive signal, and yarn characteristics will affect light received by at least one PD in the array. An output signal from a first PD is fedback to the LED driver to continuously compensate the system against dust or other factors affect LED transmission and PD light reception. An output signal from a second PD is coupled to a fraction of the drive signal so as to enhance dynamic range. This signal is amplified and AC-coupled to a sample and hold that samples during a stable active portion of the LED drive signal to demodulate the relevant signal.

Abstract: 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.

Abstract: 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.

Abstract: 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.