How Smoke Detectors Work

Smoke detectors are very helpful to us, and they are amazing inventions, because they save thousands of lives each year. Did you know how smoke detectors work? Let me tell you.

Generally speaking, the smoke detectors have two main parts--the sensor system to sense smoke, and an alarming system, which can send out warnings. It is easy to figure out how they work basically, right? According to the sensor types, the smoke detectors can have many types. I will show you two most common types to you, and tell you how they work. Ionization detectors and photoelectric detectors are the most common smoke detectors. First, let’s know the ionization smoke detectors.

Ionization detectors consist of two metal plates, with one positively charged and the other negatively charged.

A small amount of a radioactive element ionizes the air by stripping an electron off the oxygen and nitrogen atoms in the air. The negatively charged free electrons are attracted to the positively charged plate, while the oxygen and nitrogen ions are attracted to the negatively charged plate. This flow of ions creates a small, steady electric current between the two metal plates or electrodes. When some smoke enters the ionization chamber, it disturbs the current formed between the two plates, because the ions attach to heavy smoke particles moving not as fast as the gaseous ions, so, it reduces the current. Therefore, the sensor system senses the smoke, and sends signals to the alarming system, then, the alarming system sounds out warnings loudly. This type of smoke detectors is able to detect smoke particles that are too small to be seen with the naked eye, which makes them more adapted to detecting flaming fires.

Let’s go on with photoelectric smoke detectors. You may walk into a store or hotel, and have noticed that there is a photo beam detector used. The photoelectric smoke detectors are different with ionization smoke detectors in the sensor system--the photoelectric smoke detectors use photoelectric beam detectors instead of ionization chamber as the sensor part. When there is a heavy smoke crossing the beam of light, the smoke blocks the beam. Then, the photo beam detector senses the lack of light and triggers the alarming system. However, there are two problems here: it's a pretty big smoke detector, and it is not very sensitive. So, you know that the photoelectric smoke detectors use a light source and a photoelectric detector. Usually, in this type of smoke detectors, there is a T-shaped chamber where a beam of light is discharged across the horizontal bar of the T. Under normal conditions, the light beam crosses the top of the T in a straight line. However, when there is heavy smoke, it scatters the light, and then the alarming system is activated.

Did you get how the smoke detectors work? I am sure you have. Wish this article can help you to expand your knowledge.