Ionization fire detection device

Claim 2

A fire detection device comprising an enclosure, a grid at one end of the enclosure, which is permeable to gases and defines a gas collection space, a reference ionization chamber and an unsaturated measuring ionization chamber, said chambers being connected in series and each containing a source of radioactive radiation for ionizing the gas therein, said enclosure having apertures in its lateral wall, said unsaturated measuring chamber being located in said enclosure and opening at one end in the gas collection space defined by said grid and having at its other end passages which communicate with said apertures, whereby the gas surrounding the detection device can flow through said unsaturated measuring chamber, a common electrode extending into both of said chambers, and having an intermediate point thereof connected in an eLectric control circuit including alarm means and being responsive to changes in the ionization in said unsaturated chamber and reacting to said changes.

Claim 3

A fire detection device as claimed in claim 1, wherein said circuit comprises said electrode which is common to said two ionization chambers, a transistor whose base is connected to said intermediate point of the common electrode and a gate controlled switch connected in the feed circuit of said alarm means, the gate of said switch being connected to the emitter of said transistor.

Claim 4

A fire detection device as claimed in claim 2, wherein said gate controlled switch is a thyristor.

Claim 5

A fire detection device as claimed in claim 1, wherein said alarm means comprise a signal lamp located within said enclosure.

Claim 6

A fire detection device as claimed in claim 1, comprising, on a part of said common electrode located in said unsaturated chamber, a disc which deforms the field lines inside said unsaturated measuring chamber.

Claim 7

A fire detection device as claimed in claim 1, wherein said grid is brought to zero potential.

Claim 8

A fire detection device as claimed in claim 1, wherein current is supplied to the unsaturated measuring chamber through a potentiometer circuit for setting the detection threshold of the detector.

Claim 9

A fire detection device as claimed in claim 1, wherein said unsaturated ionization chamber has a diameter less than the free mean path of the ionizing particles.

Claim 10

A fire detection device as claimed in claim 1, wherein said common electrode carries a disc which defines a chamber with said grid, a passage being provided around said disc for communication with the measuring chamber, said disc carrying a radioactive source on the face thereof facing said grid so that said chamber constitutes the reference ionization chamber and the gas collection space.

Claim 11

A fire detection device as claimed in claim 3, wherein said transistor has an input impedance whose temperature coefficient is negative and which is adapted to actuate said switch when a predetermined temperature is reached.

Claim 12

A fire detection device comprising an enclosure, a grid at one end of the enclosure, which is permeable to gases and defines a gas collection space, a reference ionization chamber and an unsaturated measuring ionization chamber, said chambers being connected in series and each containing a source of radioactive radiation for ionizing the gas therein, said enclosure having apertures in its lateral wall, said unsaturated measuring chamber being located in said enclosure and opening at one end in the gas collection space defined by said grid and having at its other end passages which communicate with said apertures, whereby the gas surrounding the detection device can flow through said unsaturated measuring chamber, a common electrode extending into both of said chambers, and having an intermediate point thereof connected in a control circuit, said control comprising in each detection device, a transistor and a gate controlled switch, the transistor having its base connected to said intermediate point of the corresponding common electrode, and its emitter connected to the gate of said switch; a first alarm device responsive to actuation of said switch of any of said detection devices and a second alarm device which is combined with said line and adapted to be actuated when a break in said line occurs.

Claim 13

A fire detection device comprising an enclosure, a grid at one end of the enclosure, which is permeable to gases and defines a gas collection space, a reference ionization chamber and an unsaturated measuring ionization chamber, said chambers being connected in series and each containing a source of radioactive radiation for ionizing the gas therein, said enclosure having apertures in its lateral wall, said unsaturated measuring chamber being located in said enclosure and opening at one end in the gas collection space defined by said grid and having at its other end passages which communicate with said apertures, whereby the gas surrounding the detection device can flow through said unsaturated measuring chamber, a common electrode extending into both of said chambers, and having an intermediate point thereof connected in a control circuit, said control comprising in each detection device, a transistor and a gate controlled switch, the transistor having its base connected to said intermediate point of the corresponding common electrode, and its emitter connected to the gate of said switch; a first alarm device responsive to actuation of said switch of any of said detection devices and a second alarm device which is combined with said line and adapted to be actuated when a break in said line occurs.

Claim 14

An installation as claimed in claim 11, wherein each of said detection devices includes a signal lamp and a Zener diode connected in parallel with the signal lamp between said switch and said line.

Claim 15

An installation as claimed in claim 11, wherein said alarm devices are respectively actuated by a double-position or reed-type relay having different contact characteristics.

Claim 16

A fire detection device as claimed in claim 1, wherein said enclosure is earthed or brought to zero potential.

Claim 17

A fire detection device as claimed in claim 1, wherein said grid has a spherical dome shape.