Switching and control system for electric direct current resistance welding machine - with a measuring voltage source connected to the welding electrodes

摘要

The switching and control system for an electric direct current resistance welding machine includes a welding transformer (2) connected to an alternating current source (1), a rectifier circuit, especially a diode circuit (3, 4) and a welding process controller (5) which, depending on the contact between the workpieces (6, 7) and the welding electrodes (8, 9), switches on the welding current. The controller (5) includes a voltage source (10) and a measuring device (11). The terminals of the voltage source are connected to the electrodes (8, 9). The measuring device (11) measures the voltage beween the electrodes, and, when this voltage falls below a given threshold value, switches on the welding current. Alternativley, a current measuring device is used which switches on the welding current when the measuring current flowing through the electrode (8, 9) exceeds a given threshold value. The voltage or current measuring device is used as a sensor to ascertain whether the retraction drive of the electrodes have in fact separated them from the workpieces. The measuring voltage has a polarity which is opposite to the polarity of the rectifier voltage. At least one measuring lead (14, 15) is provided with an ohmic resistor (12). Such a resistor is located between the negative terminal of the voltage source (10) and the connection of the measuring device (11). USE/ADVANTGE - In welding equipment. It is inexpensive, and allows the contact between the workpieces and welding electrodes to be reliably determined.