Particle detector with dust rejection

A sensing system for detecting particles in an air volume, the sensing system including:

• an inlet from the air volume for introducing an airflow into the sensing system;
• a first airflow path for directing a first portion of the airflow from the inlet to a first detection chamber, the first detection chamber including detection means for detecting the level of particles within the first portion of the airflow and outputting a first signal indicative of the level of particles within the first portion of the airflow;
• a second airflow path for directing a second portion of the airflow from the inlet to a second detection chamber, the second detection chamber including detection means for detecting the particles within the second portion of the airflow and outputting a second signal indicative of the level of particles within the second portion of the airflow;
• particle reduction means arranged in the first airflow path upstream of the first detection chamber;
• and
• processing means adapted for receiving the first and second signals and comparing the first signal to a predetermined threshold level, wherein if the first signal is above the threshold level the processing means then compares the first and second signals and generates an output signal based on the relative difference between the first and second signals.

A sensing system for detecting particles in an air volume, the sensing system forming part of an aspirating smoke detector and including:

• an inlet from the air volume for introducing an airflow into the smoke detector;
• a first airflow path for directing a first portion of the airflow from the inlet to a first detection chamber, the first detection chamber including detection means for detecting the level of particles within the first portion of the airflow and outputting a first signal indicative of the level of particles within the first portion of the airflow;
• a second airflow path for directing a second portion of the airflow from the inlet to a second detection chamber, the second detection chamber including detection means for detecting the level of particles within the second portion of the airflow and outputting a second signal indicative of the level of particles within the second portion of the airflow;
• particle reduction means arranged in the first airflow path upstream of the first detection chamber;
• processing means adapted for receiving the first and second signals and comparing the first signal to a predetermined threshold level, wherein if the first signal is above the threshold level the processing means then compares the first and second signals and generates an output signal based on the relative difference between the first and second signals;
• and
• wherein if the first and second signals differ by less than a predetermined threshold percentage the processor outputs a signal indicating that smoke is present and an alarm is triggered, and wherein if the first and second signals differ by more than a predetermined threshold percentage the processor outputs a signal that dust is present and the processor modifies its detection logic to reduce the probability of an alarm.