code: def read_data(self,variable_instance):
          
          if self.inst is None:
              return
          if variable_instance.visavariable.device_property.upper() == 'PRESENT_VALUE':
              return self.parse_value(self.inst.query('?U6P0'))
          elif variable_instance.visavariable.device_property.upper() == 'PRESENT_VALUE_DCV':
              return self.parse_value(self.inst.query('?U6P0F1T3'))
          elif variable_instance.visavariable.device_property.upper() == 'PRESENT_VALUE_ACV':
              return self.parse_value(self.inst.query('?U6P0F2T3'))
          elif variable_instance.visavariable.device_property.upper() == 'PRESENT_VALUE_DCV+ACV':
              return self.parse_value(self.inst.query('?U6P0F3T3'))
          elif variable_instance.visavariable.device_property.upper() == 'PRESENT_VALUE_2W_OHM':
              return self.parse_value(self.inst.query('?U6P0F4T3'))
          elif variable_instance.visavariable.device_property.upper() == 'PRESENT_VALUE_4W_OHM':
              return self.parse_value(self.inst.query('?U6P0F5T3'))
          return None
docs: read values from the device