code: def get_voltage(self, channel):
          
          ret = self.ask("V%dO?" % channel)
          if ret[-1] != "V":
              print("ttiQl355tp.get_voltage() format error", ret)
              return None
          return float(ret[:-1])
docs: channel: 1=OP1, 2=OP2, AUX is not supported