Dust discrimination for sensing systems

A method of sensing particles in an air volume, the method comprising:

• drawing air from the air volume and causing airflow along a main airflow path past a collection site;
• inducing a localized increase in particle speed at the collection site, relative to air speed along the remainder of the main airflow path using an auxiliary airflow path from the main airflow path, the auxiliary airflow path having an exit upstream of the collection site;
• and
• testing an air sample drawn from the collection site.

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

• a main airflow path which is substantially straight, the main airflow path including an inlet from the air volume;
• a collection site in the form of a sample tube projecting into the main airflow path, the sample tube for drawing an air sample from the main airflow path;
• and
• means to induce a localized increase in particle speed at the collection site relative to air speed along the remainder of the main airflow path, the means to induce the localized increase in particle speed at the collection site comprising a venturi in the main airflow path, with the collection site being disposed along the venturi.

A method of sensing particles in an air volume, the method comprising:

• drawing air from the air volume and causing airflow along a substantially straight main airflow path past a collection site;
• inducing a localized increase in particle speed at the collection site, relative to air speed along the remainder of the main airflow path, by the use of a venturi in the main airflow path, with the collection site being disposed along the venturi;
• inducing a transverse airflow along a transverse flow path which is transverse to the main airflow path;
• and
• testing the transverse airflow.

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

• a main airflow path including an inlet from the air volume;
• a collection site for drawing an air sample from the main airflow path;
• means to induce a localized increase in particle speed at the collection site relative to air speed along the remainder of the main airflow path, the means to induce the localized increase in particle speed at the collection site comprising a venturi in the main airflow path with the collection site being disposed along the venturi;
• and
• a smoke detector for testing the air sample.

A method of sensing smoke particles in an air volume, the method comprising:

• drawing air from the air volume and causing airflow along a main airflow path past a collection site;
• inducing a localized increase in particle speed at the collection site, relative to air speed along the remainder of the main airflow path, by the use of a venturi in the main airflow path, with the collection site being disposed along the venturi;
• inducing a sample flow away from the main airflow path;
• and
• testing the sample flow for smoke particles.