Water full alarm circuit

Shown is a water full alarm circuit . When working, the switches S1 and S2 are closed. When the water level in the water tank rises to the specified depth
, the two induction pieces are conducted through the water in the water tank, causing the relay kA to absorb the table: at this time, an alarm can be sounded through the electric speaker , which is safe. The green light goes out and
the red light glows. The whole machine can be packed into a small plastic box. a:b The sensing piece should be installed at the upper limit of the water tank, with a distance of 2cm between the two pieces.