A conventional humidifier disclosed in a Taiwan patent No. 367023 is a first known one, which includes two sensors directly arranged in a water tank for checking the water level. Its major disadvantage is that the sensor may give out a wrong signal in case of the water tank still having some water if the humidifier is inclined, and cannot cut off power in due time, causing danger to a user.
Another Taiwan patent No. 145330 disclosed a humidifier, a second known one that includes a water chamber in the bottom base, a magnetic switch fixed in the water chamber, a float provided in a water tank and having a magnet to correspond to the magnetic switch. When the water level in the water tank falls down, the magnet may actuate the magnetic switch to turn off power. Then this second conventional humidifier has the same disadvantage as the first one.
Another humidifier disclosed in a U.S. Pat. No. 6,259,860B1 is invented by the same applicant of this case, a third conventional humidifier that has a water tank with an outlet, which has a water groove, and a float disposed around a connective rod of a water stopper. Then the float actuates a water level sensor fixed in a base of a body for sensing the water level. This third conventional humidifier has a disadvantage that some water still remains in the water tank in case of the humidifier is inclined improperly, and a humidifier in the invention does not have this drawback.
One more conventional humidifier disclosed in a U.S. Pat. No. 4,563,313 has a float disposed in a water tank, having the same disadvantage as those described above.
Further, another disadvantage in those conventional humidifiers is too much water in the water tank, so it takes too long time for boiling by the heater for producing vapor.