Abstract: To order to determine a distortion angle in a textile material fed in a specific feeding direction, the textile material is monitored by means of a first detection means, the output signal of which depends on an angular position of said means with respect to the feeding direction and to the distortion angle. This first output signal is filtered so that signal components that are at least statistically independent of the distortion angle are filtered out. The filtering means used comprise a band-pass filter which is adjustable with respect to its center band-pass frequency, its bandwidth and/or the shape of its filter-curve shape by means of a second output signal from a second detection means. The second output signal is dependent on the frequency characteristic of those signal components in the first output signal that are at least statistically dependent on the distortion angle.

Abstract: A particle flux counter apparatus utilizing light extinction. The apparatus utilizes two oppositely disposed cylindrical mirrors (21a, 21b) to bounce a beam back and forth between them, the beam traversing the length of the cylindrical mirrors (21a, 21b) in incremental steps. A plane mirror (22) is cooperatively located to reflect the beam back between the system to traverse the length of the cylindrical mirrors (21a, 21b) a second time in incremented steps. The two sets of steps interleaving such that the beam forms a sheet of light. A detector (60) monitors the intensity of the beam. As particles in a sample aerosol intersect the beam, the light is extinguished and the beam intensity changes. The detector (60) transmits a signal to a microprocessor (108) analyzation. The apparatus also utilizes a feedback circuit (300) to regulate the beam intensity and alternatively provides for modulating the beam to provide for higher peak power into the detector (60) and elimination of common mode noise.