US Patent No. 9,117,359

PHOTOELECTRIC SMOKE DETECTOR AND PROCESS FOR TESTING THE PHOTOELECTRIC SMOKE DETECTOR


Patent No. 9,117,359
Issue Date August 25, 2015
Title Photoelectric Smoke Detector And Process For Testing The Photoelectric Smoke Detector
Inventorship Thomas Hanses, Feldkirchen-Westerham (DE)
Gerhard Gruener, Riemerling (DE)
Wolfgang Werkmeister, Poing (DE)
Joerg Tuermer, Ebersberg (DE)
Assignee Robert Bosch GmbH, Stuttgart (DE)

Claim of US Patent No. 9,117,359

1. A photoelectric smoke detector (1) for detecting smoke particles (4), the smoke detector (1) comprising:
a light emitting element (5),

a light receiving element (6) for receiving light (8) emitted by the light emitting element (5) and scattered by the smoke particles (4) and for outputting a detection signal (12) obtained by photo-electrically converting the received light (10, 11),

an amplifier circuit (13) for amplifying the detection signal (12) and providing an amplified output signal (14), wherein the amplified output signal (14) may be divided into an offset-signal (20) and an amplified detection signal (21),

whereby the photoelectric smoke detector (1) is adapted to operate in a pulsed mode, so that the detection signal (12) comprises high-frequency components,

characterized in
that the amplified detection signal (21) is determined by high-frequency components of the detection signal (12) and that the offset-signal (20) is determined based on the detection signal (12),

whereby the amplifier circuit (13) is adapted to transfer the high-frequency components with a higher gain and to transfer the low-frequency components with
a lower gain in order to improve the signal ratio between the amplified detection signal (21) and the offset-signal (20).