Method and apparatus for detecting temperature variation utilizing the Curie point of a ferromagnetic material

DETAILED DESCRIPTION We claim: 1.
A method for detecting temperature variation above or below a predetermined value, comprising: a.
transmitting an electrical signal of short duration along an electrical circuit in thermal contact with the area where the temperature variation is to be detected wherein the electrical circuit comprises: 1.
at least two substantially parallel conductors insulated from each other; and 2.
2.
ferromagnetic material having a Curie point about equal to the predetermined temperature positioned between said parallel conductors; b.
detecting a reflection of the electrical signal; and c.
measuring the time interval between transmitting the signal and detecting the reflection thereof.
2.
The method of detecting temperature variation set forth in claim 1, further comprising: calculating from the time interval measurement the length of the electrical circuit along which the electrical signal travelled until a reflection thereof occurred.
3.
The method of detecting temperature variation set forth in claim 2, further comprising: a.
transmitting subsequently a second electrical signal from the other end of the electrical circuit; b.
detecting a reflection of the second signal; c.
measuring the time interval between transmitting the second signal and detecting the reflection thereof; and d.
calculating the length of the electrical circuit along which the second signal travelled until a reflection thereof occurred.
4.
The method for detecting temperature variation set forth in claim 3, wherein the electrical signal of short duration comprises: a pulse of voltage.
5.
The method for detecting temperature variation set forth in claim 4, wherein: the substantially parallel conductors are insulated from each other by insulation material and the ferromagnetic material is dispersed in the insulation material.
6.
The method of detecting temperature variation according to claim 5, wherein the electrical circuit comprises: a co-axial cable.
7.
The method of detecting temperature variation set forth in claim 6, wherein the ferromagnetic material comprises: soft ferrite material