Fluid lever sensor circuit design using ac signal

A very simple fluid lever sensor can be designed using this circuit diagram .
This fluid level sensor circuit is designed for using an ac sensing signal to eliminate electrolytic corrosion on the probes .The ac signal rectified is used to drive T1 transistor that drives a 12 volt relay , that can activate or stop some device . R2 resistor is used to modify the sensor sensitivity and can be replaced with a small variable resistor . MC104093B is a p channel quad 2 input NAND schmitt trigger and is pin to pin compatible with the CD4093 . The unused inputs must be tied to an appropriate voltage level , either ground or +12 volts (8,9,12 and 13) and the unused outputs must be left open (10 and 11) .
The circuit can be powered with an input voltage between 3 and 18 volts dc , but in our case the circuit use a 12 volts DC power source .