A device for converting an electrical current includes at least one phase module with an AC connection and at least one DC connection. A common light source can be used to perform edge exposure for the substrates on the first and second mounting tables, for example, at the same time, so that a high processing ability can be offered and an increase in size of the apparatus can be prevented. The system further includes a phase detector configured to detect a phase difference between the I channel output of the RF receiver and the Q channel output of the RF receiver. Currently the job is done by hand which is very slow and tedious.