A logic system is required that will sound a buzzer if the conditions within a PCB etching tank are incorrect. The buzzer must operate if the state of three sensors is as follows:
· Sensor A is ON and B is ON but C is OFF
· Sensor A is ON but B and C are both OFF
· Sensor B is ON but A and C are both OFF
· Sensors B and C are both ON but A is OFF
Under all other conditions the buzzer must not operate.