Double chamber ionization smoke detector

In a combustion product detector comprising two radioactive sources and two ionization chambers each comprising an electrode, one of said chambers being vented to the ambient atmosphere through one of said electrodes and the other chamber adapted to serve as a reference and substantially partially surrounded by said venting electrode, the combination characterized by:

• p1 said venting electrode provided with an aperture to receive a test member, and
• a test member comprising an electrically non-conductive portion and an electrically conductive portion,
• said test member supported to extend through said aperture into said vented chamber to provide said electrically conductive portion substantially inside said chamber and said electrically non-conductive portion substantially outside said chamber with said electrically conductive portion in electrical contact with said venting electrode,
• biasing means providing a biasing force to bias said test member away from said venting electrode,
• said test member manually moveable against said biasing force to extend further into said chamber to produce a change in the ionization current in said chamber,
• said electrically conductive portion being grounded through a resistor.

In a combustion product detector comprising two radioactive sources and two ionization chambers each comprising an electrode, one of said chambers being vented to the ambient atmosphere through one of said electrodes and the other chamber adapted to serve as a reference and substantially partially surrounded by said venting electrode, the combination characterized by:

• said two sources each consisting of radioactive material deposited on a surface of a plate member,
• a source holder member comprising a shouldered recess,
• said plate members received in said shouldered recess with said sources disposed to radiate in opposite directions,
• said plate members retained in said recess by staked portions of said source holder member,
• said recess adapted to be provided with different apertures through which rays may be emitted from each of said sources whereby amounts of radiation emitted to each of said chambers may be varied by providing holder members having such apertures of different sizes without changing the dimensions of said plates or the characteristics of said deposited radioactive material.