# US 2014/0197956 A1 · Particle detector with dust rejection > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2014/0197956 A1 - Document ID: US20140197956A1 - Status: Published application - Kind: A1 - Application number: 14/127,984 - Filed: 2012-06-21 - Published: 2014-07-17 - Earliest claimed: 2011-06-22 - Assignees: Xtralis Technologies Ltd. - Inventors: Brian Alexander; Kemal Ajay - Web page: https://patentgrep.com/patent/US20140197956A1 ## CPC - G08B 17/10: Actuation by presence of smoke or gases {, e.g. automatic alarm devices for analysing flowing fluid materials by the use of optical means} - G08B 29/24: Self-calibration, e.g. compensating for environmental drift or ageing of components - G08B: SIGNALLING SYSTEMS, e.g. PERSONAL CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS ## Abstract A system and method of reducing the incidence of false alarms attributable to dust in smoke detection apparatus. The method includes obtaining at least two sample air flows, subjecting a first airflow to particle reduction and measuring the level of particles in the first airflow and generating a first signal indicative of the intensity. The method also includes measuring the level of particles in the second airflow and generating a second signal indicative of the intensity. The first signal is compared to a predetermined alarm level and, if the alarm level is achieved, the first and second signals are subsequently compared and an output signal is generated based on the relative difference between the first and second signals. ## Claims ### Claim 1 A method of particle detection including; analysing a first air sample from an air volume being monitored and determining a level of first particles in the first air sample; analysing a second air sample from the air volume and determining a level of second particles in the second air sample; processing the level of first particles in the first air sample and/or level of second particles in the second air sample in accordance with at least one first alarm criterion; and in the event that at least one criterion is met: performing differential processing of the level of first particles in the first air sample and level of second particles in the second air sample in accordance with at least one second alarm criterion; and in the event that one second alarm criterion is met; and performing an action. ### Claim 2 (depends on 1) The method according to claim 1, wherein the step of performing an action includes sending a signal indicative of: an alarm or fault condition, a change in an alarm or fault condition, a pre-alarm or pre-fault condition or other signal, a signal indicative of either or both of the level of first or second particles. ### Claim 3 (depends on 1) The method according to claim 1, wherein the second particles include particles of interest and nuisance particles, and the first particles substantially exclude nuisance particles. ### Claim 4 (depends on 1) The method according to claim 1, including filtering the second air sample to create the first air sample. ### Claim 5 (depends on 1) The method according to claim 1, wherein analysis of the second air sample only occurs in the event that the level of first particles in the first air sample meets the at least one first alarm criterion. ### Claim 6 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. ### Claim 7 (depends on 6) The system according to claim 6, wherein the particle reduction means acts to reduce the quantity of larger particles within the first portion of the airflow. ### Claim 8 (depends on 6) The system according to claim 6, wherein the first signal is compared to a threshold alarm level of particle intensity. ### Claim 9 (depends on 6) The system according to claim 6, wherein in the event that dust is present in the air volume the processor acts to modify its detection logic to reduce the probability of an alarm. ### Claim 10 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. ### Claim 11 (depends on 10) The system according to claim 10, wherein the threshold percentage is 20-40%. ### Claim 12 A method of reducing the incidence of false alarms attributable to dust in smoke detection apparatus, the method including obtaining at least two sample air flows, subjecting a first airflow to particle reduction and measuring the level of particles in the first airflow and generating a first signal indicative of the intensity, measuring the level of particles in the second airflow and generating a second signal indicative of the intensity, comparing the first signal to a predetermined alarm level and, if the alarm level is achieved, subsequently comparing the first and second signals and generating an output signal based on the relative difference between the first and second signals. ### Claim 13 (depends on 12) The method according to claim 12 further including temporarily modifying the behaviour of the smoke detector based on the output signal. ### Claim 14 (depends on 6) The system according to claim 6, wherein the first and second detection chambers are a single detection chamber having first and second input airflow paths. ### Claim 15 (depends on 14) The system according to claim 14, wherein each of the first and second airflow paths further include valve means for selectively allowing one of the first and second airflow paths to pass to the detection chamber. ### Claim 16 (depends on 15) The system according to claim 15, wherein the particle reduction means is located in the first airflow path intermediate the respective valve means and the detection chamber.