On-board thermostat and a system for detecting excess temperature

1. A thermal detection and visual alarm unit comprising a plurality of first expansion thermal detectors ( 17 ) with normally closed contacts that are connected in series with a first lamp ( 15 ) to form a first two-terminal circuit ( 21 , 23 ), a plurality of second expansion thermal detectors ( 18 ) with normally open contacts connected in parallel, a second lamp ( 16 ) connected in series with the second thermal detectors to form a second two-terminal circuit ( 22 , 24 ), the first and second thermal detectors forming a plurality of cells ( 19 ) each combining a first detector and a second detector having respective contact-opening or contact-closing temperatures that are substantially equal, each of said first and second two-terminal circuits being arranged for connection to the terminals of an electrical power supply ( 12 ).

2. A unit according to claim 1 , in which:

each of said cells for detecting transition through a transition temperature comprises a strip or structure suitable for deforming by differential expansion and for switching over, at said transition temperature, from a first position in which a normally closed contact is closed to a second position in which a normally open contact is closed and a normally closed contact is opened, and vice versa; and

at least one and preferably each of the cells further includes an electrically conductive element that is movable relative to the deformable strip or structure, together with a member provided for placing the moving conductor element in contact with the deformable strip or structure so as to cause, in said first configuration, the normally open contact to close.

3. A unit according to claim 1 , in which at least one of said cells includes an element bearing against a strip or structure that is deformable by expansion, together with a member for causing deformation of said deformable strip or structure by pressing the bearing element thereagainst, the deformation being sufficient to open the normally closed contact and to close the normally open contact.

4. A unit according to claim 2 , in which the moving conductor element or bearing element is secured to a support that is mounted to move relative to a substantially sealed housing containing the deformable strip or structure.

5. A unit according to claim 4 , in which the moving support is urged by a spring towards a position in which the conductor or bearing element is not active.

6. A unit according to claim 4 , in which said moving support is displaced by exciting an electromagnetic circuit.

7. A system ( 11 ) for detecting fire on board an aircraft, the system comprising:

an electrical power supply ( 12 ); and

a plurality of detection cells ( 19 ), each cell being provided in a zone to be monitored of the aircraft and comprising a first expansion thermal detector ( 17 ) with normally closed contacts together with a second expansion thermal detector ( 18 ) with normally open contacts, the respective changeover temperatures of the first and second detectors of a cell being equal or close, the cells being connected in cascade and forming a monitoring equipotential or line ( 13 ) and a fault line ( 14 , 14 ′), a lamp being inserted in each of these two lines, the two lines being connected, in parallel, across the terminals of the electrical power supply.

8. A system according to claim 7 , in which:

each of said cells for detecting transition through a transition temperature comprises a strip or structure suitable for deforming by differential expansion and for switching over, at said transition temperature, from a first position in which a normally closed contact is closed to a second position in which a normally open contact is closed and a normally closed contact is opened, and vice versa; and

at least one and preferably each of the cells further includes an electrically conductive element that is movable relative to the deformable strip or structure, together with a member provided for placing the moving conductor element in contact with the deformable strip or structure so as to cause, in said first configuration, the normally open contact to close.

9. A system according to claim 7 , in which at least one of said cells includes an element bearing against a strip or structure that is deformable by expansion, together with a member for causing deformation of said deformable strip or structure by pressing the bearing element thereagainst, the deformation being sufficient to open the normally closed contact and to close the normally open contact.

10. A system according to claim 8 , in which the moving conductor element or bearing element is secured to a support that is mounted to move relative to a substantially sealed housing containing the deformable strip or structure.

11. A system according to claim 10 , in which the moving support is urged by a spring towards a position in which the conductor or bearing element is not active.

12. A system according to claim 10 , in which said moving support is displaced by exciting an electromagnetic circuit.