Electrical current saving combined smoke and fire detector

• US 5,831,537 A
• Filed: 10/27/1997
• Issued: 11/03/1998
• Est. Priority Date: 10/27/1997
• Status: Expired due to Fees

• Current Assignee: GE Security Incorporated (Carrier Global Corporation)
• Original Assignee: SLC Technologies, Inc. (General Electric Company)
• Inventors: Marman, Douglas H.
• Primary Examiner(s): Hofsass, Jeffery A.
• Assistant Examiner(s): LA, ANH V
• Application Number:
  US08/958,628
• Time in Patent Office: 372 Days
• Field of Search: 340/628, 340/629, 340/630, 340/632, 340/522, 340/286.05, 340/635
• US Class Current: 340/628
• CPC Class Codes: G08B 17/117 by using a detection device for specific gases, e.g. combustion products, produced by the fire G08B17/103, G08B17/11 take precedence
• CPC Class Codes: G08B 29/043 of fire detection circuits

Abstract

A fire detection system (10) includes a smoke detector (52) that measures smoke particle density indicative of smoldering fires and a CO₂ detector (90) that measures CO₂ concentration indicative of flaming fires. In a first operating current saving method, the smoke detector is operated at a normal PRF while the CO₂ detector is operated at a very slow PRF. Smoke density measurements (14) produced by the smoke detector are compared with a set of tentative fire detection criteria (18, 20, 22, 14), and if met, the CO₂ detector PRF is substantially increased to rapidly produce CO₂ concentration measurements (26) that are compared to a set of conclusive fire detection criteria (30, 32, 36, 38). In a second operating current saving method, the CO₂ detector is operated at a normal PRF while the smoke detector is operated at a zero PRF. CO₂ concentration measurements produced by the CO₂ detector are compared with a set of tentative fire detection criteria (30, 32, 36, 38), and if met, the smoke detector PRF is substantially increased to rapidly produce smoke density measurements that are compared to a set of conclusive fire detection criteria (18, 20, 22, 24). In a reliability improving operating method, electrical current draw and/or signal presence of the smoke and CO₂ detectors are monitored to determine whether either detector has failed. If a failure is detected, fire detection criteria normally employed are changed to criteria optimized for the remaining detector.

Claims

1. In a fire detection system including a first detector that generates in response to first pulses a first signal representative of a first measurement and a second detector that generates in response to second pulses a second signal representative of a second measurement, a method of reducing operating current drawn by the fire detection system in response to the first and second pulses, comprising:

applying the first pulses to the first detector at a first pulse repetition frequency ("PRF");

applying the second pulses to the second detector at a second PRF that is substantially less than the first PRF;

comparing the first signal to a predetermined set of tentative fire detection criteria;

determining whether a member criterion of the predetermined set of tentative fire detection criteria is satisfied, and if it is;

increasing the second PRF to a third PRF that is substantially greater than the second PRF;

comparing at least one of the first and second signals to a predetermined set of conclusive fire detection criteria; and

generating an alarm signal if any member criterion of the predetermined set of conclusive fire detection criteria is satisfied.

2. The method of claim 1 in which the first detector is a smoke detector and the first measurement is a smoke particle concentration measurement, and in which the second detector is a CO₂ detector and the second measurement is a CO₂ concentration measurement.

3. The method of claim 2 in which the second PRF is less than about 2 pulses per minute.

4. The method of claim 2 in which the third PRF is greater than about 10 pulses per minute.

5. The method of claim 2 in which the predetermined set of tentative fire detection criteria include exceeding a smoke threshold level ranging from about 0.25 to about 0.5 percent light obscuration per 0.3048 meter.

6. The method of claim 2 in which the predetermined set of conclusive fire detection criteria include exceeding a threshold rate of increase in a concentration of CO₂ ranging from about 100 to about 1,000 parts-per-million per minute.

7. The method of claim 1 in which the first detector is a CO₂ detector and the first measurement is a CO₂ concentration measurement, and in which the second detector is a smoke detector and the second measurement is a smoke particle concentration measurement.

8. The method of claim 7 in which the second PRF is substantially zero pulses per minute.

9. The method of claim 7 in which the predetermined set of tentative fire detection criteria include exceeding a threshold rate of increase in a concentration of CO₂ ranging from about 100 to about 1,000 parts-per-million per minute.

10. The method of claim 7 in which the predetermined set of conclusive fire detection criteria include exceeding a smoke threshold level of 1.0 percent light obscuration per 0.3048 meter.

11. The method of claim 1 in which the first and second detectors are enclosed within a unitary smoke and fire detector housing.

12. The method of claim 1 in which the at least two of the first, second, and third PRFs are controlled by a centralized control panel.