Who knows how to calculate the span?

The smoke moved upward and reached the bottom of smallpox. Smoke detectors detect fires through smoke. When you don't see the flame or smell the smoke, the smoke sensor already knows. It works 24 hours a day 365 days a year. When an alarm is sounded, it will make a harsh sound until the smoke clears. In a real fire, it worked until it was burned down. Ion sensors work by measuring the balance of positive and negative charges in air. Inside the sensor, there is a small piece of radioactive material, which can generate tiny current in the air flowing in the induction chamber. On the circuit board, there is a computer chip to monitor this current. When smoke particles enter the induction chamber, it will disturb the balance of positive and negative charges there and change the current. When the smog gradually increases, the imbalance between positive and negative charges will be strengthened. When this balance reaches a certain limit, the horn will ring.