import smbus

class MQUnifiedsensor:
    def __init__(self, ...): # other initialization parameters
        self._sensor_volt = 0
        self._adc = 0
        self._VOLT_RESOLUTION = 0
        self.addr = 0x30  # I2C address, assumed to be 0x30 as per your context
        # Initialize other necessary variables and states

    def update(self):
        bus = smbus.SMBus(1)  # 1 indicates /dev/i2c-1
        try:
            data = bus.read_i2c_block_data(self.addr, 0, 2)
            self._adc = data[0] | (data[1] << 8)
            self._sensor_volt = self._adc / 1024.0 * self._VOLT_RESOLUTION
        except IOError:
            # Handle error (e.g., device not connected)
            pass
        finally:
            bus.close()