Television camera measuring devices

A device for monitoring the molten zone of a semi-conductor rod in a crucible free melting system comprising a television camera having a vidicon tube for monitoring the melting zone and in which an image of the melting zone is projected onto said vidicon tube and in which said vidicon tube is scanned by an electron beam, a deflection coil for scanning said electron beam in the horizontal direction, a saw tooth generator connected to said deflection col and providing an alternating current thereto, a resistor connected between said saw tooth generator and said deflection coil, a rectifier connected to said resistor and producing a direct current which is analogous to the peak value of said alternating current supplied to said deflection coil, a reference voltage, a potentiometer connected across said reference voltage, a comparison circuit having inputs connected to said rectifier and said potentiometer and supplying an output indicative of the difference in values of the inputs, and an amplitude adjusting means in said saw tooth generator which receives the output of said comparison circuit to control the amplitude of the alternating current output supplied to said deflection coil.