![]() ![]() If the torch is operating at the low current level when contact is made, no action is required by the circuit, system or method. Another object of the present invention is the provision of a circuit, system and method, as defined above, which circuit, system and method senses contact between the nozzle and workpiece and immediately shifts the plasma arc torch from a high current operation at a high set point current to a low current operation at a lower set point current or to a maximum current level. The primary object of the present invention is the provision of a circuit, system and method for protecting a plasma arc torch from damage when the nozzle of the torch engages the workpiece or another grounded plate. The power supply is not turned off which would cause the arc to be extinguished and require restriking of the arc and restarting procedures for the plasma cutting operation. ![]() In accordance with the invention, the power supply is phased back to a low current mode of operation or low current level. Contact is also signaled when the torch is laid against a grounded metal plate which simulates workpiece contact. This low voltage indicates contact of the nozzle and the workpiece. The detection employs a voltage divider to indicate when the voltage between the nozzle and workpiece is less than 5.0 volts. Shifting the current control means in the second mode in response to the contact detection. This method involves the steps of detecting contact of the workpiece and nozzle to thus identify a serious wear condition and holding, i.e. In accordance with another aspect of the invention, the protective circuit as defined above is used as a method of protecting the nozzle of a plasma torch of the type comprising a nozzle with a plasma outlet opening and an internal chamber and an elongated electrode in the chamber and spaced from the nozzle a distance defining an annular gas passage means for allowing flow of a plasma gas through the passage means and through the outlet for the impingement against a spaced workpiece to be cut. This high set point current can be substantially above 50 amperes. ![]() The first mode of operation can be defined as a set current in the general range of 75-100 amperes however, broadly speaking the power supply in the first mode of operation, which is considered the high current mode of operation, is at a current set point substantially above the low or second current mode of operation. ![]()
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