Heat detector with shape metal alloy element

Patent metadata

Field	Value
Publication number	US-9524841-B2
Application number	US-201314137138-A
Country	US
Kind code	B2
Filing date	Dec 20, 2013
Priority date	Dec 21, 2012
Publication date	Dec 20, 2016
Grant date	Dec 20, 2016

Abstract

A temperature sensing system comprises a conductive tube, a shape memory alloy (SMA) element, and a detector. The SMA element is disposed to create an electrical contact with the electrical tube when subjected to at least a critical temperature, and the detector is configured to identify an alarm condition when the conductive tube and the SMA element form a closed electrical circuit.

First claim

The invention claimed is:

1. A temperature sensing system comprising:
a conductive tube;
a shape memory alloy (SMA) element disposed to create an electrical connection with the conductive tube when subjected to at least a critical temperature; and
a detector configured to identify an alarm condition when the conductive tube and the SMA element form a closed electrical circuit; and
a piezoresistive sleeve disposed between the SMA element and the conductive tube, and configured to act as a conductor when strained by a shape change of the SMA element.

2. The temperature sensing system of claim 1 , wherein the SMA element is disposed within the conductive tube.

3. The temperature sensing system of claim 1 , further comprising:
a volume of gas enclosed within the conductive tube; and
a pressure transducer configured to sense thermal expansion of the volume of inert gas, and thereby sense distributed temperature along the conductive tube.

4. The temperature sensing system of claim 3 , wherein the pressure transducer is a diaphragm switch selected to close at a distributed overheat temperature.

5. The temperature sensing system of claim 3 , wherein the pressure transducer is a continuous pressure sensor.

6. The temperature sensing system of claim 1 , further comprising:
a support structure configured to retain the SMA element at a separation distance from the conductive tube when below the critical temperature.

7. The temperature sensing system of claim 6 , wherein the support structure comprises:
a core disposed concentrically within the conductive tube to support the SMA element; and
a spacer extending between the core and the concentric tube to distance the core and the SMA element from the conductive tube.

8. The temperature sensing system of claim 7 , wherein the SMA element is a helix or spring disposed about the core.

9. The temperature sensing system of claim 7 , wherein the spacer is a helix or spring disposed between the core and the conductive tube.

10. The temperature sensing system of claim 7 , wherein the SMA element is adhered to the core in at least two locations.

11. The temperature sensing system of claim 1 , wherein the piezoresistive sleeve is a flexible membrane that is deformed by a shape change of the SMA element.

12. The temperature sensing system of claim 1 , wherein the SMA element is a helix or spring disposed that radially expands to compress the piezoresistive sleeve at temperatures above the critical temperature.

13. The temperature sensing system of claim 1 , wherein the detector further comprises a data processor configured to flag an alarm condition whenever the SMA element forms a closed circuit with the conductive tube.

14. The temperature sensing system of claim 1 , wherein the detector connects to and identifies alarm conditions from a plurality of conductive tubes and a plurality of corresponding SMA elements.

15. The temperature sensing system of claim 1 , wherein the SMA element is formed of a Nickel-Titanium alloy.

Assignees

• Kidde Tech Inc

Inventors

• Rennie Paul
• Dutson Beth A
• Smith Paul D
• Dunster Robert G

Classifications

• H01H61/0107 Primary

  making use of shape memory materials · CPC title

• G01K5/483

  using materials with a configuration memory, e.g. Ni-Ti alloys · CPC title

• H01H37/323 Primary

  making use of shape memory materials (in thermal relays H01H61/0107; release mechanism H01H71/145; treatment of SMF alloys C22F1/006; for control of temperature G05D23/024) · CPC title

• H01H37/40

  with diaphragm · CPC title