Optical arrangement in hot box detection apparatus

Claim 1

IMPROVED OVERHEATED RAILROAD JOURNAL BOX DETECTION APPARATUS OF THE TYPE HAVING AN INFRARED SENSITIVE ELEMENT MOUNTED NEAR THE GROUND ADJACENT A RAILROAD TRACK AND AIMED TO RECEIVE RADIATION FROM JOURNAL BOXES PASSING ABOVE, SAID APPARATUS COMPRISING AN OPTICAL ARRANGEMENT DISPOSED SUCH THAT ITS OPTICAL AXIS INTERCEPTS THE JOURNAL BOXES ON A MOVING RAILROAD VEHICLE FOR FOCUSING SAID RADIATION ONTO SAID INFRARED SENSITIVE ELEMENT, SAID OPTICAL ARRANGEMENT INCLUDING A PLURALITY OF LENSES SUBSTANTIALLY TRANSPARENT TO INFRARED RADIATION AND OPAQUE TO OTHER RADIATION AND A HIGH SPEED SHUTTER, SAID SHUTTER BEING DISPOSED AT THE FOCAL POINT OF THE FIRST OF SAID LENSES SO THAT SHUTTER TRAVEL BETWEEN A FIRST POSITION, WHEREIN THE RADIATION FROM A JOURNAL BOX IS PERMITTED TO BE FOCUSED ON SAID INFRARED SENSITIVE ELEMENT BY SAID OPTICAL ARRANGEMENT, AND A SECOND POSITION, WHEREIN ALL RADIATION EXCEPT THAT EMANATING FROM SAID SHUTTER IS PREVENTED FROM REACHING SAID INFRARED SENSITIVE ELEMENT, IS A MINIMUM, SAID OPTICAL ARRANGEMENT INCLUDING SAID FIRST LENS TO RECEIVE THE SUBSTANTIALLY PARALLEL RAYS EMITTED FROM A JOURNAL BOX AND TO FOCUS THEM AT ITS FOCAL POINT, A SECOND LENS TO RECEIVE THE DIVERGING RADIATION FROM SAID FOCAL POINT AND