Photoelectric control device for a flaw detector for moving webs

Claim 1

IN A FLAW DETECTOR FOR MOVING WEBS, HAVING MEANS FOR DIRECTING A LIGHT BEAM TOWARD A SURFACE OF A MOVING WEB INCLUDING MEANS FOR CONVERGING THE LIGHT BEAM TO A LIGHT SPOT ON THE WEB AND FOR MOVING THE SPOT PERPENDICULARLY TO THE DIRECTION OF MOVEMENT OF THE WEB, FURTHER HAVING PHOTOELECTRIC MEANS POSITIONED TO BE RESPONSIVE TO THE REFLECTION OF SAID LIGHT SPOT BY THE WEB AND PRODUCING A FLAW DETECTOR SIGNAL, FURTHER HAVING A CONTROL SIGNAL GENERATOR RESPONSIVE TO THE PASSAGE OF SAID LIGHT SPOT OVER THE EDGES OF THE WEB AND PRODUCING AN ENABLING SIGNAL WHEN SAID SPOT ENTERS AND A DISABLING SIGNAL WHEN IT LEAVES THE WEB, THE COMBINATION COMPRISING: CIRCUIT MEANS INCLUDING A VARIABLE DIFFERENTIATING STAGE AND A GATE CONNECTED TO SAID PHOTOELECTRIC MEANS SO AS TO BE RESPONSIVE TO SAID FLAW DETECTOR SIGNAL, CIRCUIT MEANS FOR FEEDING SAID ENABLING AND DISABLING SIGALS TO SAID GATE FOR GATING SAID FLAW DETECTOR SIGNAL, SWITCH MEANS CONNECTED TO SAID DIFFERENTIATING STAGE FOR CONTROLLING THE VARIATION THEREOF, AND CIRCUIT MEANS FOR FEEDING SAID ENABLING AND DISABLING SIGNALS TO SAID SWITCH MEANS SO THAT THE TIME CONSTANT OF SAID DIFFERENTIATING STAGE IS INCREASED AFTER SAID ENABLING SIGNAL DECREASED AFTER SAID DISABLING SIGNAL.