Self-adjusting smoke detector with self-diagnostic capabilities

摘要

A smoke detector (10) has internal self-adjustment and self-diagnostic capabilities. It includes a microprocessor-based alarm control circuit (24) that periodically checks the sensitivity of a smoke sensing element (20) to a smoke level in a spatial region (12). The alarm control circuit and the smoke sensor are mounted in a discrete housing (25) that operatively couples the smoke sensor to the region. The microprocessor (30) implements a routine (50) stored in memory (32) by periodically determining a floating adjustment (FLT-ADJ) that is used to adjust the output (RAW-DATA) of the smoke sensing element and of any sensor electronics (40) to produce an adjusted output (ADJ-DATA) for comparison with an alarm threshold. The floating adjustment is not greater than a maximum value (ADJISENS) or less than a minimum value (ADJSENS). Except at power-up or reset, each floating adjustment is within a predetermined slew limit of the immediately preceding floating adjustment. The floating adjustment is updated with the use of averages (NEW-AVG) of selected signal samples taken during data gathering time intervals having a data gathering duration that is long in comparison to the smoldering time of a slow fire. The adjusted output is also used for self-diagnosis.