Ionization and Photoelectric Sensors
Usually the greatest volume of smoke is produced during ignition and smouldering stages. There are many different types of smoke detector but the 2 most prevalent are ionization and photoelectric.
Ionization Detectors are triggered by both visible and invisible fire by-products but respond best to actual flames. They contain a source of low radiation that produces electrically charged ions. These sensors have a long lifespan because they do not require a lot of energy to work and therefore also need very little maintenance. They are not suitable for use in applications in an environment with high ambient radioactivity levels as this reduces the sensitivity of the sensor.
Photoelectric Detectors can either be in the form of a beam or light scattering sensor and are best suited to detecting smoke from a smouldering fire. With the beam model, when smoke interferes with the beam and changes its trajectory the alarm is activated. Smoke reflects light particles so in the light scattering model the detector senses the light, which activates the alarm.
For smoke detection we use both ionised and optical sensors.