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Laser Protection in a Particulate Matter Sensor by a Pulsed Mode Operation Disclosure Number: IPCOM000258782D
Publication Date: 2019-Jun-13

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The laser current rises with higher temperatures. The lifetime of lasers reduces significantly with higher laser currents. Thus high temperatures reduce the lifetime of lasers. Self-heating of the laser during operation in a particulate matter sensor increases the laser temperature compared to ambient temperature. In a sensor housing, this can be up to 20°C more for the laser compared to ambient. Self-heating in a particulate matter sensor reduces therefore the lifetime of the laser. In order to protect the laser and increase the lifetime of the laser in a particulate matter sensor, the duty cycle of the laser can be reduced as soon as the laser current exceeds a certain threshold. For example, the laser is then only turned on for 1 second every 5th second. The laser is then operated in a Pulsed Mode. Self-heating is reduced substantially in this situation. When the temperature rises even higher, the laser can even be turned off completely to ensure its survival. After cool down, it will be turned on again. Also the particulate matter sensor operation and sensor output has to be adjusted accordingly.