Control device for a resistance-type flash butt welder

A control device is proposed for a resistance-type flash butt welder which contains a welding transformer 1 in whose primary winding a welding current transmitter 7 is connected. The welding current transmitter 7 is connected to an electrohydraulic drive 30 for displacing the movable machine plate via a control unit 12 of the drive. According to the invention, the control unit 12 of the drive is designed in the form of two difference amplifiers 14 and 15, in which one set of inputs is connected to the output of the welding current transmitter 7, and a desired-voltage source 13 is connected to the other inputs of the difference amplifiers 14 and 15. The output of each of the difference amplifiers 14 and 15 is connected via one transistor 21, 22 each and one voltage divider 25, 26 each to the input of an operational amplifier 29. The voltage of the one or the other voltage divider 25, 26 applied to the input of the operational amplifier 29, by its sign, which is different for the two voltage dividers 25, 26, determines the direction of movement of the electrohydraulic drive. The output of the operational amplifier 29 is connected to the input of the electrohydraulic drive 30, and a unit 6 for keeping the welding voltage constant is connected in the primary circuit of the welding transformer 1, the control input of this unit 6 being connected to the secondary winding of the welding transformer 1.