Abstract: Methods, apparatus and systems for detecting an arc during supplying a plasma process in a plasma chamber with a power are provided. An example plasma power supply includes: a DC source, an output signal generator, a first signal sequence measurement device for measuring a first signal sequence present between the DC source and the output signal generator, a second signal sequence measurement device for measuring a second signal sequence present at an output of the output signal generator, and a controller configured to generate a reference signal sequence based on one of the first and second signal sequences, to compare the reference signal sequence and the other of the first and second signal sequences that has not been used to determine the reference signal sequence, and to generate a detection signal if the reference signal sequence and the other of the first and second signal sequences cross.