Plasma cutters use a number of methods to start the pilot arc. These will often depend upon the age of the machine and the environment it is being used in.
Older plasma cutters have a pilot arc that utilises high frequency, high voltages and a spark gap to conduct electricity through the air. However, in this high tech modern age high frequency
can interfere with sensitive equipment, computers or office equipment that may be in use in the local area.
The HF method has other areas of concern such as risk of electrocution, machine maintenance, difficulty of repair and spark gap maintenance, in addition to its RF (radio frequency) emissions.
Due to these problems, alternate methods of starting were developed that eliminate the potential problems associated with high frequency starting circuits where plasma cutters work near sensitive electronics, such as CNC hardware or computers.
One starting method is via a capacitive discharge into the primary circuit through an SCR (silicon controlled rectifier). This releases a short high energy burst to create a spark to transfer the arc. The ‘blow apart’ arc method features the tip and electrode initially in contact within the torch head. When the torch trigger is operated, a current flows between the electrode and the tip.
As the plasma gas flows it will move the electrode and tip apart creating a spark and a pilot arc is then established. The transfer from pilot to cutting arc occurs when the pilot arc is brought in close to the work piece. This transfer is caused by the electric potential from tip to work via the ionised gas stream.
Another HF free method is via a spring loaded design in the plasma torch head. The trigger is operated and the torch pressed against the material to be cut. This creates a short circuit between the tip and electrode and current starts to flow. As the physical pressure is released the pilot arc is established and the main arc is transferred by proximity to the work piece or via contact cutting where the tip remains in contact with the work piece.