Fault detection apparatus of a web-fed rotary printing press

Error detection means (1) for detecting a running substantially parallel to a web edge web break or the like defect of a printing material web (3) in a printing machine, with two are arranged on the opposing web edges, transversely or obliquely to the printing substrate (3) movable web-edge detectors (5a, 5b), each of the web edge detectors associated tracking Stel drives (7a, 7b) for tracking the respective web edge detector (5a, 5b) with respect to shifting of a transversal web edge, two each having a tracking actuator (7a, 7b) associated with the tracking detectors (17a, 17b) for detecting the amount of a tracking or the current position of the corresponding web edge detector (5a, 5b) and a (to outputs of the tracking detectors 17a, 17b) evaluation unit (19) connected, characterized, in that the evaluation unit (19) is formed into a comparative processing of the tracking amounts at both web edges according to a predetermined comparison algorithm and for outputting a signal if the processing result of the comparison processing meets a predetermined error criterion, and that the web edge detectors (5a, 5b) in each case two are arranged at a predetermined distance from one another, vertically, or ...