Practical and improved fire detector

• US 5,691,704 A
• Filed: 01/29/1996
• Issued: 11/25/1997
• Est. Priority Date: 01/29/1996
• Status: Expired due to Term

• Current Assignee: GE Security Incorporated (Carrier Global Corporation)
• Original Assignee: Engelhard Sensor Technologies, Inc. (BASF SE)
• Inventors: Wong, Jacob Y.
• Primary Examiner(s): Hofsass, Jeffery
• Assistant Examiner(s): LA, ANH V
• Application Number:
  US08/593,750
• Time in Patent Office: 666 Days
• Field of Search: 340/628, 340/630, 340/629, 340/286.05, 340/632, 340/522
• US Class Current: 340/628
• CPC Class Codes: 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
• CPC Class Codes: G08B 17/113 Constructional details
• 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 29/183 Single detectors using dual technologies G08B13/1672, G08B13/2448, G08B13/2494 take precedence
• CPC Class Codes: G08B 29/20 Calibration, including self-calibrating arrangements

Abstract

A fire detector which combines an NDIR CO₂ gas detector with a photoelectric smoke detector to minimize false alarms by logic means that can be integrated into a single chip that can have an ASIC section and a microprocessor section. The NDIR CO₂ detector can be single or dual channel. The NDIR CO₂ gas detector and the photoelectric smoke detector can be separate or combined in a single device in which they are optically isolated by a light-tight barrier but still use a common light source. Also, the CO₂ and smoke detectors can be combined on a single substrate within a common housing.

Claims

1. A fire detector, comprising:

a smoke detector;

a non-dispersive infrared (NDIR) carbon dioxide (CO₂) sensor;

logic means for generating an alarm signal when any of the following criteria are met;

light obscuration exceeds a threshold level for greater than a first preselected time;

light obscuration exceeds a reduced threshold level for greater than a second preselected time;

or

light obscuration exceeds the reduced threshold level and the rate of increase in the concentration of CO₂ exceeds a predetermined rate; and

an alarm responsive to the alarm signal.

2. A fire detector as recited in claim 1, wherein the smoke detector is a photoelectric smoke detector.

3. A fire detector as recited in claim 2, wherein the photoelectric smoke detector uses a silicon photodiode.

4. A fire detector as recited in claim 2, wherein the NDIR CO₂ sensor uses a single-channel micro-machined silicon thermopile as an infrared detector.

5. A fire detector as recited in claim 4, wherein the logic means relies on the rate of change in CO₂ concentration to detect the rate of increase in the concentration of CO₂.

6. A fire detector as recited in claim 5, wherein the logic means is integrated into an application specific integrated circuit (ASIC) chip.

7. A fire detector as recited in claim 4, wherein the NDIR CO₂ sensor uses a thin film narrow bandpass interference filter having a center wavelength at 4.26 microns and a full width at half maximum (FWHM) of 0.2 microns.

8. A fire detector as recited in claim 2, wherein the NDIR CO₂ sensor uses a dual-channel silicon micron-machined thermopile detector with a built-in temperature sensor in intimate thermal contact with a reference junction of the thermopile as an infrared detector.

9. A fire detector as recited in claim 8, wherein the logic means measure a ratio between outputs of the two detector channels of the thermopile detector to calculate CO₂ concentration.

10. A fire detector as recited in claim 9, wherein the logic means is integrated into a signal process chip.

11. A fire detector as recited in claim 10, wherein the signal processor chip uses a microprocessor section to calculate the ratio and determine the rate of change for CO₂.

12. A fire detector as recited in claim 8, wherein the NDIR CO₂ sensor uses a thin film narrow bandpass interference filter having a center wavelength at 4.26 microns and a FWHM of 0.2 microns for a first channel and a neutral filter centered at 3.91 microns and a FWHM of 0.2 microns for a second channel.

13. A fire detector as recited in claim 2, wherein the NDIR CO₂ sensor uses a differential source gas analysis technique.

14. A fire detector as recited in claim 13, wherein the logic means is integrated into a signal processing chip that includes an ASIC section and a microprocessor section.

15. A fire detector as recited in claim 14, wherein the microprocessor section generates pulsing wave forms to drive an infrared source used in the differential source gas analysis technique.

16. A fire detector as recited in claim 2, wherein the smoke detector and the NDIR CO₂ sensor are combined in a single device but optically isolated from one another.

17. A fire detection system, comprising:

a detector assembly, comprising;

a case;

a housing contained within the case;

a substrate within the housing;

a thermopile detector fabricated on the substrate;

a silicon photodiode mounted on the substrate;

a light-tight barrier that separates and optically isolates the thermopile detector from the silicon photodiode and forms a carbon dioxide detector channel and a smoke detector channel within the case;

a light source mounted within the case;

a carbon dioxide filter located between the light source and the thermopile detector in the carbon dioxide detector channel;

a specularly reflective gas sample chamber formed between the light source and the thermopile detector in the carbon dioxide detector channel;

means for circulating gas into and out of the gas sample chamber; and

a smoke detector scattering chamber formed between the light source and the silicon photodiode in the smoke detector channel;

an alarm; and

a signal processor connected to the alarm and the detector assembly which contains logic means for generating an alarm signal when any of the following criteria are met;

light obscuration exceeds a threshold level for greater than a first preselected time;

light obscuration exceeds a reduced threshold level for greater than a second preselected time;

or

light obscuration exceeds the reduced threshold level and the rate of increase in the concentration of carbon dioxide (CO₂) exceeds a predetermined rate; and

an alarm responsive to the alarm signal.

18. A smoke detector assembly as recited in claim 17, wherein the silicon photodiode is fabricated on the substrate.

19. A smoke detector assembly as recited in claim 17, wherein the signal processor is integrated into a single chip.

20. A smoke detector assembly as recited in claim 17, wherein the signal process generates pulsing wave forms to drive the light source.