Water Level Controller

Water Level Controller

       Water level controller switches on the pump as soon as water in upper tank goes below lower level and switches off when water reaches upper level. It also prevents motor from dry running by monitoring water level in lower tank. If water in lower tank is below lower level, unit will switch off the pump. Total five stainless steel probes are used, three for upper tank and two for lower. The upper tank probes monitor lower and reference level respectively. The basic principle of water level controller is conductivity of the water. IC1, IC2 are CD 4093 quad 2 input NAND gate ICs. When all five probes are under water the input of N3, N5, N7 are logic 0. This keeep gate N6 output at logic 1 and motor will be off. As water level starts falling down, first it will go below 'UTUL' (Upper Tank Upper Level) probe. The input to gate N5 goes 1 and output of N4 goes 1 to reset the latch formed by N1, N2. As water level further goes down below 'UTLL' probe, input t gate N3 will high and pin 10 will be low to set the latch. The latch output pin 3 changes the output of N6 from 1 to 0 and subsequently the output of N8 to high which further drives transistor T1, T2 in emmiter follower mode to actuate relay. The relay contacts will switch on the motor. Now water starts filling tank. Though it crosses 'UTLL' probe, motor will not stop due to latch. The latch will reset when water reaches 'UTUL' probe and motor will stop. If water in the lower tank is below 'LTLL' probe it will change the output of N7 from 1 to 0 and stops the motor immediately to prevent dry running. Reduce values of R1, R2, R3 if circuit is not functioning due to change in conductivity.

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