# US 4,396,840 A · Ionization type smoke sensing device > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 4,396,840 A - Document ID: US4396840A - Status: Granted - Kind: A - Application number: 06/192,715 - Filed: 1980-10-01 - Granted: 1983-08-02 - Earliest claimed: 1980-10-01 - Assignees: Matsushita Electric Works, Ltd. - Inventors: Tsunehiko Araki; Yoshihiko Okuda; Takeshi Nakano - Web page: https://patentgrep.com/patent/US4396840A ## CPC - H01J 47/02: Ionisation chambers - G08B 17/11: using an ionisation chamber for detecting smoke or gas - G08B 17/113: Constructional details - H01J: ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS (spark-gaps H01T; electric arc lamps H05B31/00; particle accelerators H05H) - G08B: SIGNALLING SYSTEMS, e.g. PERSONAL CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS ## Abstract An ionization type smoke sensing device includes a printed board. An inner electrode made of heat-resistant metal is attached to the printed board and a radioactive source is fixed to the inner electrode. An outer electrode in the form of a bottomed cylinder made of heat-resistant metal and adapted to cover the inner electrode extends through the printed board and is integrally joined to a protective lid member made of heat-resistant metal at the back of the printed board. Therefore, the outer electrode and the lid member cooperate with each other to define an ionization chamber. The outer electrode is formed with smoke inlet ports for introducing smoke into the ionization chamber. The electric circuit serves to give pulse signals of a relatively high voltage to the outer electrode and to detect the presence of smoke on the basis of the amount of a current flowing through the inner electrode. ## Claims ### Claim 1 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. ### Claim 2 (depends on 1) An ionization type smoke sensing device as set forth in claim 1, wherein said insulating material includes synthetic resins. ### Claim 3 (depends on 2) An ionization type smoke sensing device as set forth in claim 2, wherein said printed board has a sufficiently larger area than the area of said opening in said outer electrode and is disposed to cover said opening, and said outer electrode and said lid member are integrally joined together while extending through said printed board. ### Claim 4 (depends on 3) An ionization type smoke sensing device as set forth in claim 3, wherein said inner electrode is fixed to said printed board, whereby said inner electrode is fixed to said lid member through said printed board. ### Claim 5 (depends on 4) An ionization type smoke sensing device as set forth in claim 4, wherein said printed board includes a first conductive foil constituting said electric circuit means and electrically connected to said inner electrode through which said first conductive foil extends, and a second conductive foil constituting said electric circuit means and electrically connected to said outer electrode. ### Claim 6 (depends on 5) An ionization type smoke sensing device as set forth in claim 5, wherein said printed board further includes a third conductive electrode disposed between said first and second conductive foils and serving to prevent leakage current from flowing between said first and second conductive foils. ### Claim 7 (depends on 6) An ionization type smoke sensing device as set forth in claim 6, wherein said third conductive foil acts as a grounding electrode. ### Claim 8 (depends on 7) An ionization type smoke sensing device as set forth in claim 7, wherein said electric circuit means includes a first resistor attached to said printed board and electrically connected between said first and third conductive foils, and a second resistor attached to said printed board and electrically connected between said second and third conductive foils. ### Claim 9 (depends on 1) An ionization type smoke sensing device as set forth in claim 1, which further comprises a housing, said housing being adapted to accommodate the integral combination of said outer electrode and lid member, and at least some of the circuit parts constituting said electric circuit means. ### Claim 10 (depends on 9) An ionization type smoke sensing device as set forth in claim 9, wherein said housing includes a first portion acting as a base, and a second portion cooperating with said first portion to constitute said housing. ### Claim 11 (depends on 10) An ionization type smoke sensing device as set forth in claim 10, which further comprises a second smoke inlet port formed in said second portion. ### Claim 12 (depends on 11) An ionization type smoke sensing device as set forth in claim 11, wherein said first portion includes a base, a lateral wall formed on the peripheral edge of said base, and a first engaging portion formed on the inner surface of said lateral wall, and wherein said second portion includes a lateral wall adapted to be fitted in the lateral wall of said first portion, a cover portion extending from said lateral wall, and a second engaging portion on said lateral wall for engaging said first engaging portion. ### Claim 13 (depends on 12) An ionization type smoke sensing device as set forth in claim 12, which further comprises a clearance formed between said two lateral walls at a position associated with said engaging portions, and an undercut portion formed in said base to communicate with said clearance. ### Claim 14 (depends on 13) An ionization type smoke sensing device as set forth in claim 13, wherein said first and second members are made of synthetic resin. ### Claim 15 (depends on 14) An ionization type smoke sensing device as set forth in claim 14, wherein said insulating member includes synthetic resin. ### Claim 16 (depends on 15) An ionization type smoke sensing device as set forth in claim 15, wherein said insulating member is constructed as the printed board for attaching thereto electric parts constituting said electric circuit means, said housing receives said printed board, said first portion is disposed on the back side of said printed board, and said second portion is disposed on the face side of said printed portion. ### Claim 17 (depends on 16) An ionization type smoke sensing device as set forth in claim 16, which further comprises two power source connecting portions provided on said base, and connecting leads respectively extending from said two power source connecting portions through said base and connected to the power source circuit means for the electric circuit formed on said printed board. ### Claim 18 (depends on 17) An ionization type smoke sensing device as set forth in claim 17, wherein said printed board is disposed to cover the opening in said outer electrode, said outer electrode and said lid member extends through said printed board and being integrally joined together, and said inner electrode is fixed to said printed board. ### Claim 19 (depends on 18) An ionization type smoke sensing device as set forth in claim 18, which further comprises a first shield member interposed between said printed board and said base, a second shield member extending along the inner surface of said second portion, and a third smoke inlet port formed in said second shield member and communicating with said smoke inlet ports. ### Claim 20 (depends on 19) An ionization type smoke sensing device as set forth in claim 19, which further comprises a partition plate attached to said first shield member and preventing flowing-out of smoke which has entered said shield member. ### Claim 21 (depends on 20) An ionization type smoke sensing device as set forth in claim 20, which further comprises a second insulating sheet for prevention of electrical contact between said outer electrode and said second shield member. ### Claim 22 (depends on 13) An ionization type smoke sensing device as set forth in claim 13, wherein said base is formed with a throughgoing hole in connection with said undercut portion.