Frequency limit setting is Not available under DC-
INT, AC+DC-EXT, AC-EXT, AC+DC-Sync and AC-
Sync output modes.
Before change freq limit setting, if FREQ setting
value is bigger than desire freq limit value, the freq
limit value cannot be change accordingly.
The range of frequency limit will be limited within
the certain minimum value in accordance with the
output frequency setting.
There are 2 sets of frequency limits in total.