Smoke detectors
An aspirated smoke detector includes a flow path and a generator of acoustic waves in the flow path. Airborne particulate matter in the flow path responds to the acoustic field by particle agglomeration; the resulting larger particles flow into a photoelectric-type smoke sensor. A sensed level of particles can be processed, or compared to one or more predetermined thresholds to establish presence of one or more predetermined conditions.
1. A smoke detector comprising:
a housing;
a flow path for ambient atmosphere carried by the housing;
a source of ultrasonic signals carried by the housing, the source generating an acoustic field of a predetermined intensity in at least a portion of the flow path; and
a smoke sensor coupled to the path, the sensor receives particulate matter carried by the ambient atmosphere in the flow path subsequent to that particulate matter having been exposed to the acoustic field where the acoustic field coagulates particulate matter carried by the ambient atmosphere prior to that particulate matter entering a sensing region of the sensor.
2. A detector as in claim 1 which includes an aspirating element that induces movement of ambient atmosphere along the flow path.
3. A detector as in claim 1 where the source comprises an ultrasonic transducer.
4. A detector as in claim 3 which includes an aspirating element that induces movement of ambient atmosphere along the flow path.
5. A detector as in claim 4 where the sensor comprises at least one of an optical-type sensor, an ionization-type sensor, a gas sensor and a thermal sensor.
6. A detector as in claim 4 where the aspirating element moves the particulate matter to a sensing region of the sensor.
7. A detector as in claim 1 where the sensor comprises one of an optical-type or an ionization-type sensor particulate sensor.
8. A detector as in claim 7 where the sensor comprises a photo-electric type smoke sensor.
9. A detector as in claim 8 which includes control circuits coupled to the transducer and the sensor.
10. A detector as in claim 9 where the aspirating element includes an electrically actuatable flow inducing member.
11. A detector as in claim 10 where control circuits are coupled to the aspirating element.
12. A detector as in claim 11 which includes a filter in the flow path.
13. A detector as in claim 7 where the acoustic field extends, in part, into the sensing region.
14. A method comprising:
producing a flow of particulate carrying ambient atmosphere to be sensed;
generating an acoustic field of a selected intensity;
directing the flow through the field thereby producing a flow of coagulated particles; and
sensing the coagulated particles and which includes comparing sensed coagulated particles to a predetermined level and generating an output signal indicative thereof.
15. A method as in claim 14 which includes confining the acoustic field at a predetermined region.
16. A method comprising:
producing a flow of particulate carrying ambient atmosphere to be sensed;
generating an acoustic field of a selected intensity;
directing the flow through the field thereby producing a flow of coagulated particles;
sensing the coagulated particles and which includes energizing a selected transducer to produce the acoustic field.
17. A method as in claim 16 where energizing includes producing a standing wave resonant acoustic field in the region.