Ionization type smoke sensing device

An ionization type smoke sensing device comprising:

• an outer electrode in the form of a bottom cylinder made of heat-resistant metal and having an opening,
• a lid member made of heat-resistant metal, integrally joined to said outer electrode to close said opening in said outer electrode and cooperating with said outer electrode to define an ionization chamber,
• an insulating member comprising a printed circuit board containing electrical elements for forming an electrical circuit,
• an inner electrode fixed to said lid member through said insulating member and disposed in said ionization chamber,
• a radioactive source fixed to said inner electrode so as to be faced toward the bottom of said outer electrode, and
• smoke inlet ports formed in said outer electrode and sized such that they are sufficiently large to introduce smoke into said ionization chamber but sufficiently small to prevent the radioactive source fixed to said inner electrode from escaping therethrough,
• said electrical circuit means applying a voltage for ionization of said radioactive source to said outer electrode and detecting entry of smoke into said ionization chamber through said smoke inlet ports based on the amount of electrical current flowing into said outer electrode, and
• said lid member being fixed to the outer electrode by the extension of the outer electrode through the printed circuit board to the rear side thereof whereby the lid member serves as a fixture for fixing the outer electrode to the printed circuit board.