Rapid fire detector

A fire detector having no moving parts and which senses the concentration of carbon dioxide in the ambient air, comprising in combination;

• differential temperature source means including a radiating element and including means for alternating the temperature of said radiating element from T.sub.1 to T.sub.2 and from T.sub.2 to T.sub.1 while the fire detector is in use for producing radiation having a first spectrum when the temperature is T.sub.1 and having a second spectrum when the temperature is T.sub.2 ;
• a sample chamber containing air and including a passage communicating with the ambient air, said sample chamber including means defining a path for the produced radiation through said sample chamber;
• a dual pass band filter located in the path and having two pass bands, one of which is centered at a wavelength L.sub.2 at which carbon dioxide has an absorption band and the other of which is centered at a wavelength L.sub.1 at which the air in said sample chamber does not absorb radiation, for simultaneously passing radiation within the two pass bands;
• detector means for intercepting radiation that has passed through said dual pass band filter and through said sample chamber and for converting the intercepted radiation to an electrical signal;
• circuit means responsive to said electrical signal and to said means for alternating the temperature for determining the concentration of carbon dioxide in the air within said sample chamber and for producing a signal representative of that concentration;
• and,
• alarm means responsive to the signal produced by said circuit means for producing an alarm in accordance with a preset criterion;
• said differential temperature source means, said sample chamber, said dual pass band filter, said detector means, said circuit means, and said alarm means all remaining stationary when the fire detector is in use.

A fire detector having no moving parts and which senses the concentration of carbon dioxide in the ambient air, comprising in combination:

• differential temperature source means including a radiating element and including means for alternating the temperature of said radiating element from T.sub.1 to T.sub.2 and from T.sub.2 to T.sub.1 while the fire detector is in use for producing radiation having a first spectrum when the temperature is T.sub.1 and having a second spectrum;
• a sample chamber containing air and including a passage communicating with the ambient air, said sample chamber including means defining a path for the produced radiation through said sample chamber;
• a dual pass band filter located in the path and having two pass bands, one of which is centered at a wavelength L.sub.2 at which carbon dioxide has an absorption band and the other of which is centered at a wavelength L.sub.1 at which the air in said sample chamber does not absorb radiation, for simultaneously passing radiation within the two pass bands;
• detector means for intercepting radiation that has passed through said dual pass band filter and through said sample chamber and for converting the intercepted radiation to an electrical signal;
• circuit means responsive to said electrical signal and to said means for alternating the temperature for determining the rate of change of the concentration of carbon dioxide in the air within said sample chamber and for producing a signal representative of that rate;
• and,
• alarm means responsive to the signal produced by said circuit means for producing an alarm in accordance with a preset criterion;
• said differential temperature source, said sample chamber, said dual pass band filter, said detector means, said circuit means and said alarm means all remaining stationary when the fire detector is in use.