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Incipient fire detector II

  • US 4,764,758 A
  • Filed: 07/01/1987
  • Issued: 08/16/1988
  • Est. Priority Date: 07/01/1987
  • Status: Expired due to Fees
First Claim
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1. A new and improved incipient fire detector having sample gas selector valve and conduit system means for selectively sampling the gaseous atmospheres in a multiplicity of different volumetric spaces automatically and sequentially supplying the sampled gases to a centrally located small particle detector, said gaseous atmosphere sampling conduit system including an improved gas sample flow rate deviation detector which operates in a stable manner over a wide range of temperatures to detect any variation in flow rate of the sampled gases through the sampling conduct system from a preset norm, and wherein said gas flow rate deviation detector comprises a pair of self-heating thermistors each having the same resistance value at a known reference temperature but which have different free air dissipation constants, the thermistor with the smaller free air dissipation constant being physically mounted in the gaseous atmosphere sampling conduit system for monitoring the flow rate therethrough and the remaining thermistor being physically mounted in a region that is at the same temperature as the gaseous atmosphere being sampled but is not in a flowing stream of sampled gas, and both thermistors being electrically interconnected in a measurement circuit for deriving an output signal indicative of any deviation in the sampling flow rate of the sampled gaseous atmospheres from a preset norm, and an improved system operating condition checking sub-system comprised by particle generator means connected to the automatically operated sample gas selector valve and conduit system means for selectively injecting small particles into the samples of gaseous atmospheres supplied to the centrally located particle detector that periodically operates to sequentially sample and test the sample gases from the respective zones for the presence of particles, timing and control means coupled to the particle generator means and synchronized with the operation of the respective zone sampling periods for activating the particle generator means for a short time interval relative to the sampling period of each respective zone at the end thereof for injecting into the sample conduit system for delivering a burst of small particles to the centrally located particle detector whereby continued normal operation of the system can be indicated in low particle background environments.

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