Timing circuit that prohibits restarting

　　The above figure shows an underground oxygen concentration detection circuit, which can be used in underground operating environments to detect the oxygen concentration in the air. The oxygen concentration detection sensor in the circuit converts the detection result into a DC voltage. After passing through the circuit amplifier ICl-1 and the voltage comparator ICl-2, it drives the transistor and rri, and then rri drives the relay . After the relay operates , the contact is connected. , the buzzer sounds to remind people that the oxygen concentration is too low, attracting people's attention.