GB1085621A - Improvements in or relating to methods and devices for detecting faults - Google Patents

Abstract

1,085,621. Fault detector. P. LIPPKE. March 19, 1965 [March 21, 1964], No. 11669/65, Heading GIN. Faults in a sheet or sheets of a fibrous material, such as paper, cause variations in a capacitor formed of two plates 3, 4, Fig. 1, between which the sheets move, the capacitor 3, 4 being connected to an inductance 2, thus forming a resonant circuit which is tuned to a frequency which is different from that of an oscillator 1 connected to the inductance 2, changes in this frequency difference being used to control at 8 a sorting device. The voltage at a point 5 on the inductance 2 varies with the changes in frequency difference, and is rectified and supplied to the control device 8 via a capacitor 6 and amplifier 7. Any permissible gradual changes in sheet thickness cause a slowly changing signal at 5 which is delayed at 19, 20 and applied to an amplifier 16 which compares a signal derived by rectifying the oscillator 1 output, with the delayed measurement signal, a trimming capacitor, 18, being adjusted by a motor 17 until the resonant frequencies again differ by the required amount. This arrangement also renders the system independent of temperature and supply voltage variations. The trimmer may be in the oscillator circuit. In one embodiment Fig. 3 (not shown) two measuring capacitors, movable across the width of the sheet, have respective resonant circuits, the outputs of which are compared, and a common oscillator (not shown). In a further embodiment Fig. 4 (not shown), a plurality of capacitors, having one plate common to all, is arranged across the width of the sheet and these have their respective resonant circuits connected to "ring" fashion so that any two adjacent capacitors have their values compared, and the two outer capacitors have their values compared. The capacitors are mounted on a support member which is protected from vibrations of the associated machinery, for example by resilient blocks (56, Figs. 3 and 48, Fig. 2, not shown) or resilient lamina, (52, 53, Fig. 2, not shown). The separation of the measuring capacitor plates 3, 4, may be adjusted.