Magnetic trap suppression tank level sensor

1. A method for manufacturing a fire suppressant storage device, the fire suppressant storage device ( 20 ) comprising:

a tank ( 22 ) having a first port ( 40 ), a second port ( 70 ), and an interior ( 32 ) for storing fire suppressant;

a discharge assembly ( 46 ) mounted to the first port and comprising:

a discharge valve ( 48 ); and

a discharge conduit ( 50 ) at least partially within the interior and having:

an interior; and

an exterior; and

a liquid level measurement assembly ( 82 ; 200 ; 250 ; 300 ; 400 ) mounted to the second port and comprising:

a tube ( 100 ) at least partially within the tank interior and having:

an interior sealed relative to the surrounding tank interior; and

an exterior;

a float ( 120 ; 220 ) surrounding the tube; and

a member ( 122 ; 222 ; 252 ; 302 ) axially movable within the tube interior,

wherein:

the liquid level measurement assembly is a second liquid level measurement assembly;

one of the float and the member comprises an upper magnet ( 130 ; 230 ) and a lower magnet ( 132 ; 232 ); and

the other of the float and the member magnetically cooperates with the upper magnet and the lower magnet to relatively axially trap the member to the float,

the method comprising:

removing a first liquid level measurement assembly from the second port, the first liquid level measurement assembly comprising:

a tube at least partially within the interior and having:

an interior sealed relative to the surrounding tank interior; and

an exterior;

a float surrounding the tube and having one or more magnets at only a single axial position; and

mounting the second liquid level measurement assembly to the second port, the float of the second liquid level measurement assembly comprising said upper magnet and said lower magnet.

2. The method of claim 1 wherein:

the upper magnet and the lower magnet are polarized in the same direction.

3. The method of claim 2 wherein:

the same direction is a radial direction.

4. The method of claim 2 wherein:

the same direction is an axial direction.

5. The method of claim 1 wherein:

said one of the float and the member is the float; and

said other of the float and the member is the member.

6. The method of claim 1 wherein:

the member has a magnet ( 134 ; 234 ; 252 ; 310 ; 424 ) polarized anti-parallel to the upper magnet and the lower magnet.

7. The method of claim 1 wherein:

the upper magnet and the lower magnet are each a circumferential array of magnets.

8. The method of claim 1 wherein the liquid level measurement assembly further comprises:

means for measuring an axial position of the member.

9. The method of claim 8 wherein the means for measuring an axial position of the member is selected from the group consisting of:

a tensioned element ( 254 ) passing through an aperture in the member and means ( 260 ) for measuring a vibratory frequency of the tensioned element;

a tensioned element ( 312 ) passing through an aperture in the member and means ( 330 ) for measuring an electrical resistance of the tensioned element;

an optical position sensor ( 154 ); and

an ultrasonic position sensor ( 154 ).

10. A fire suppressant storage device ( 20 ) comprising:

a tank ( 22 ) having a first port ( 40 ), a second port ( 70 ), and an interior ( 32 ) for storing fire suppressant;

a discharge assembly ( 46 ) mounted to the first port and comprising:

a discharge valve ( 48 ); and

a discharge conduit ( 50 ) at least partially within the interior and having:

an interior; and

an exterior; and

a liquid level measurement assembly ( 400 ) mounted to the second port and comprising:

a tube ( 100 ) at least partially within the interior and having:

an interior sealed relative to the surrounding tank interior; and

an exterior;

a float ( 120 ) surrounding the tube; and

a member ( 424 ) axially moveable within the tube interior,

wherein:

the liquid level measurement assembly comprises a longitudinal array of magnetic field sensors or magnetic switches ( 402 ) within the tube;

the member has an aperture surrounding the array; and

the member has one or more magnets positioned to magnetically cooperate with one or more of the magnetic field sensors or magnetic switches for determining a position of the member along the array and with the float to relatively axially trap the member to the float.

11. The fire suppressant storage device of claim 10 further comprising:

said fire suppressant within the tank interior, the discharge conduit at least partially immersed in the fire suppressant.

12. The fire suppressant storage device of claim 11 wherein:

said fire suppressant comprises a clean agent.

13. The fire suppressant storage device of claim 11 further comprising:

a compressed gas propellant in a headspace of the tank.

14. A method for using the fire suppressant storage device of claim 10 the method comprising:

measuring a position of the member along the tube.

15. The method of claim 14 further comprising:

discharging the suppressant from the tank; and

during the discharging, repeating the measuring one or more times.

16. The fire suppressant storage device of claim 10 wherein:

said magnetic field sensors or magnetic switches are present as Hall Effect sensors or Hall Effect switches.

17. The fire suppressant storage device of claim 10 wherein:

said magnetic switches are present as reed switches.

18. The fire suppressant storage device of claim 10 wherein:

said float comprises an upper magnet and a lower magnet.

19. The fire suppressant storage device of claim 18 wherein:

said member one or more magnets is an axially polarized annular magnet.

20. The fire suppressant storage device of claim 19 wherein:

the upper magnet and the lower magnet are polarized in the same axial direction.