The photoelectric sensor is installed at the bottom of the device (or any other location as long as it can achieve this function). When the water level in the device is lower than the sensor, the sensor will give a signal to indicate the lack of water, so the device stops working and will automatically enter Water filling state; installed on the side, when the water is added to a certain position, the photoelectric liquid level sensor will also give a signal, so the device stops the water filling work to prevent the water from overflowing.