"Heat quickly" automatic power-off circuit

Working principle of the circuit : AN is the start button. When in use, the water level detection electrodes M and
IV are placed in a water bottle filled with water together with the heating tube. Press the "AN" button, and the primary voltage
of the transformer T is reduced by the heating tube and AC current is supplied. Through, after boosting, the secondary gets
an alternating current of about 12 V. After rectification by VD, VDz and the water resistance between the water level detection electrodes elbow and IV
, a smooth DC voltage of about 12 V is formed on C, providing K relay. It is used for electrical
contact suction work. K is a DC relay with an operating voltage of 12 V, and the K normally open contact is connected in parallel with AN. LED is heating indicator light. When the relay is closed, the LED lights up, the contact K is closed at the same time, and the electric heating tube EH is electrically heated. When AN is released, the K relay is in a self-locking state, and the normally open contact of K is always in a closed state. EH keeps warm and heated. When the water in the water bottle is boiled, many circulating working bubbles are formed due to severe cavitation , causing the elbow and IV to be instantly disconnected, the K coil loses power, and the K contact is disconnected, completing the task of boiling water. After that, due to the drop in water temperature, the K relay will not act and the EH heating tube will no longer work. You have to manually press the " AN " button to turn on the electricity for heating.