1372403 Photo-electric fault detectors TOKYO SHIBAURA ELECTRIC CO Ltd 11 Nov 1971 [11 Nov 1970] 52496/71 Heading G1A Tears or dirt on the edges or other boundary portions of bank-notes or other such sheets bearing a printed pattern are detected photoelectrically by an arrangement which can deal with sheets which have been fed incorrectly and are angled or shifted transversely with respect to the directions of movement. For one edge, light from lamp 17 is projected through and past edge area 12 to a linear array of photo-detectors 18a. These are arranged in the gating circuit of Fig.2, each detector channel of which is provided with a Schmitt circuit 22 whose discrimination level is set so as to produce an output when direct light is incident on the particular detector but not when light transmitted through the sheet is incident. Of three detectors 18a(i-1), 18a(i) and 18a(i+1) are considered, the first receives light wholly, via the bank-note, the second receives light passing the edge region i.e. partially through and partially direct, and the third receives direct light. The combination of inverters 23 and AND gates 24, 25 is such that only AND gate 25(i), corresponding to the edge portion itself produces an output, this being representative of an intensity level corresponding to the condition (torn, dirty &c.) at a certain distance within the edge of the bank-note (in Fig.2, given by the output of amplifier 21(i-1) delivered to one input of AND gate 25(i)). The AND gates 25 are connected to an OR-gate such that whichever is effective (depending on the transverse shift (or misorientation) of the banknote, it has its output passed to a comparison circuit 28 where the edge signal is compared with a reference signal representative of a perfect edge. Depending on the quality the note may be rejected. A duplicate photo-electric system may be provided for the lower edge. It is also possible to monitor other portions of the bank-note as long as a defined boundary exists whereby the levels of the Schmitt triggers may be set.