Sensitivity fault indication technique implemented in smoke detector system with self-diagnostic capabilities

In an automatic fire alarm communication system implemented with a conventional two-wire alarm initiating circuit that develops an alarm indication in response to an alarm signal pulse of predetermined minimum duration and predetermined magnitude, a self-diagnostic smoke detector system comprising:

• a signal sampler cooperating with a radiation sensor to produce signal samples indicative of periodic measurements of a smoke obscuration level in a spatial region;
• a processor receiving and processing the signal samples, the processor comparing the signal samples to multiple threshold values, one of the threshold values representing a smoke obscuration alarm level and another of the threshold values representing a tolerance limit for the radiation sensor, and the processor determining from the signal samples corresponding to smoke obscuration levels that exceed the alarm level and from signal samples corresponding to smoke obscuration levels that exceed the tolerance limit whether the signal samples are indicative of an alarm condition or an out-of-calibration condition of the system;
• and
• a signal generator that develops and provides to the communication system a sensitivity fault condition signal comprising a repetitive multiple-pulse sequence in response to a determination by the processor that the signal samples indicate an out-of-calibration condition, the sensitivity fault condition signal including in each sequence multiple time-displaced pulses each of which having a duration that is substantially less than the predetermined minimum duration so as to diminish the probability of approximately concurrent sensitivity fault condition signals produced by multiple smoke detector systems causing the alarm initiating circuit to generate a false alarm signal.