Process and apparatus for measuring the weft thread or course position of textile sheets

In an apparatus for measuring the draft angle of a weft thread in a continuously travelling textile sheet which comprises:

• at least one source of illumination for lighting a field of the textile sheet;
• at least one photodetector for absorbing light transmitted through or reflected from the field of the textile sheet and emitting an electric output signal;
• an evaluation means for evaluating the output signal of the at least one photodetector and emitting a signal substantially proportional to the draft angle wherein said at least one photodetector is formed as a rectilinear arrangement of a plurality of photosensor elements that can be individually scanned, said evaluation means comprising a threshold circuit means for comparing output signals of individual said photosensor elements to a threshold value, for classifying the output signals of the photosensor elements into only two classes, bright or dark, and for determining the number of the photosensor elements in the same class or the rate at which output values of the same class move over the rectilinear arrangement and determines the draft angle from the number or the rate.

An apparatus for measuring the draft angle of a weft thread in a continuously travelling textile sheet which comprises:

• at least one photodetector for absorbing light transmitted through or reflected from a field of a textile sheet and emitting an electric output signal;
• an evaluation means for evaluating the output signal of the at least one photodetector and emitting a signal substantially proportional to the draft angle wherein the at least one photodetector comprises at least two rectilinear arrays of photosensor elements which output signals are respectively proportional to the distribution of brightness on the at least one photodetector or to the positions of bright and dark classes, the longitudinal axis of the at least one photodetector forming defined angles with the travelling direction and wherein, the evaluation means comprises means comparing the change in speed or phase positions of the output signals to each other for determining the draft angle.