The water level sensor in a humidifier's automatic water level control device consists of a reed switch, a float, a pulley, and a permanent magnet. When the float moves up and down due to the rise and fall of the wave surface, the pulley and rope drive the permanent magnet up and down. When the permanent magnet moves to the set position of the reed switch, the normally open contact in the reed switch closes under the influence of the permanent magnet's magnetic field. When the permanent magnet moves away, the contact is released. The water level signal is determined by the connection and disconnection of the reed switch contacts. So, what is the working principle of a reed switch water level switch?
1. Working principle of reed tube water level switch:
A reed switch is designed at one or more points within a sealed metal or plastic tube. One or more hollow float rings containing an annular magnet are threaded through the tube. A retaining ring is used to control the position of the float and the reed switch, causing the float to float up and down within a specified range. The magnet inside the float attracts the reed switch contacts, generating an opening and closing action to control or indicate water levels.
The following figure shows the relative positions of the float switch when it is normally closed (NC) and normally open (NO):

2. Precautions for using reed tube water level switch:
1. The float does not move
① The specific gravity of the liquid is less than that of the float. Re-confirm the specific gravity of the float.
② If the float ball is leaking, please contact our company to replace the float ball;
③ Foreign matter is stuck in the float. Remove the foreign matter.
2. The float moves, but there is no signal output.
① The float position is offset → adjust the float position;
② The reed switch is damaged → Replace the reed switch.
3. The signal output is abnormal. There is magnetic field interference nearby. Eliminate the magnetic field.
4. The signal remains and cannot be restored. The float cannot return to its original position. There is a foreign object stuck. Clear it.
5. There will be two signal outputs at one point, and the ring position can be adjusted by moving one.
6. Clean the dirt on the connecting rod and float regularly (the cycle depends on the medium).
7. Check whether the screws on the buckle are loose.