Take a forced measurement.

        In forced mode, the BME sensor goes back to sleep after each
        measurement and we need to set it to forced mode once at this point,
        so it will take the next measurement and then return to sleep again.
        In normal mode simply does new measurements periodically.

def _take_forced_measurement(self):
        """Take a forced measurement.

        In forced mode, the BME sensor goes back to sleep after each
        measurement and we need to set it to forced mode once at this point,
        so it will take the next measurement and then return to sleep again.
        In normal mode simply does new measurements periodically.
        """
        # set to forced mode, i.e. "take next measurement"
        self._bus.write_byte_data(self._i2c_add, 0xF4, self.ctrl_meas_reg)
        while self._bus.read_byte_data(self._i2c_add, 0xF3) & 0x08:
            sleep(0.005)