Self-compensating projected-beam smoke detector
First Claim
1. A self-compensating high detection sensitivity projected-beam smoke detector, comprising:
- a transmitter for projecting a beam of energy through a propagation path, the path having a time-varying attenuation coefficient;
a receiver for providing a signal having a time varying characteristic that corresponds to the way that the transmitted energy is attenuated by the time varying attenuation coefficient;
means for providing time varying first data representative of the preselected characteristic of the time-varying signal;
means responsive to the first data for providing second data representative of a time-average of said time-varying signal;
periodically operative means for determining the change in said second data relative to a predetermined and time-stable reference standard;
means coupled to said receiver for varying said characteristic of said signal in an opposite sense to the sense of said change in said second data and in a degree that depends on the absolute magnitude of said change so as to substantially proportionally compensate said change in said second data and thereby stabilize said characteristic of said time-varying signal against variations induced by said time-varying attenuation coefficient;
means responsive to said stabilized characteristic of said signal for providing a signal indication of smoke detection whenever said stabilized characteristic of said signal meets a predetermined criteria;
wherein said signal having a time-varying characteristic is a voltage Vin that varies in a way that corresponds to the way that the transmitted energy is attenuated by the time varying attenuation coefficient;
wherein said means for determining the change in said second data relative to a predetermined and time stable reference standard includes means operative to provide a signal Vagc representative of said change in said second data relative to a predetermined and time-stable reference standard;
said means coupled to said receiver for varying said characteristic of said signal in an opposite sense to the sence of said change in said second data in a degree that depends on the absolute magnitude of said change so as to substantially proportionately compensate said change in said second data and thereby stabilize said characteristic of said time-varying signal includes a voltage controlled oscillator for providing a compensated signal equal to some constant times the ratio of the signal Vin with the signal Vagc ;
whereby, the compensated signal produced, being the ratio of Vin ans Xagc any changes in Vin are substantially compensated by a proportional change in Vagc.
2 Assignments
0 Petitions
Accused Products
Abstract
A modular transceiver head including cooperative cover and base members operable as a transmitter or as a receiver of infrared energy. The cover member includes a window defining a comparatively wide field of view in azimuth and in elevation. An optical train including a gimbaled specular member that is mounted to the base member readily allows both rough and fine adjustment of the pointing direction of the specular member anywhere within the field of view of the cover member window. A controller including a processor is coupled to a transceiver head pair respectively operative as a transmitter and as a receiver of infrared energy to controllably project a beam of infrared energy therebetween through a protected region. The controller is operative to de-sensitize the beam against potential electrically interferring effects present along the beam path. The controller is periodically operative in a self-test mode to reduce the intensity of the projected-beam to simulate a smoke condition. The controller is periodically operative in a self-compensation mode to compensate for long and short term beam degredation effects such as pollution variation normally encountered along the beam path arising in the normal operation of the protected region and to compensate for film build-up on the elements of the transceiver head optical trains. The controller is cooperative with a watch-dog timer to monitor its own operating state. Plural alalrm thresholds are operator selectable to provide enhanced confidence detection, and particularized signal indications are provided to readily and quickly identify possible alarm and trouble conditions.
47 Citations
12 Claims
-
1. A self-compensating high detection sensitivity projected-beam smoke detector, comprising:
-
a transmitter for projecting a beam of energy through a propagation path, the path having a time-varying attenuation coefficient; a receiver for providing a signal having a time varying characteristic that corresponds to the way that the transmitted energy is attenuated by the time varying attenuation coefficient; means for providing time varying first data representative of the preselected characteristic of the time-varying signal; means responsive to the first data for providing second data representative of a time-average of said time-varying signal; periodically operative means for determining the change in said second data relative to a predetermined and time-stable reference standard; means coupled to said receiver for varying said characteristic of said signal in an opposite sense to the sense of said change in said second data and in a degree that depends on the absolute magnitude of said change so as to substantially proportionally compensate said change in said second data and thereby stabilize said characteristic of said time-varying signal against variations induced by said time-varying attenuation coefficient; means responsive to said stabilized characteristic of said signal for providing a signal indication of smoke detection whenever said stabilized characteristic of said signal meets a predetermined criteria; wherein said signal having a time-varying characteristic is a voltage Vin that varies in a way that corresponds to the way that the transmitted energy is attenuated by the time varying attenuation coefficient; wherein said means for determining the change in said second data relative to a predetermined and time stable reference standard includes means operative to provide a signal Vagc representative of said change in said second data relative to a predetermined and time-stable reference standard; said means coupled to said receiver for varying said characteristic of said signal in an opposite sense to the sence of said change in said second data in a degree that depends on the absolute magnitude of said change so as to substantially proportionately compensate said change in said second data and thereby stabilize said characteristic of said time-varying signal includes a voltage controlled oscillator for providing a compensated signal equal to some constant times the ratio of the signal Vin with the signal Vagc ; whereby, the compensated signal produced, being the ratio of Vin ans Xagc any changes in Vin are substantially compensated by a proportional change in Vagc. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
-
Specification