Here is a product that I bet you have never seen before! A heat detecting cable manufactured by Patol Ltd. This is a revolutionary innovative product that acutely detects heat with no electronics or sensors. The cable itself is the sensor.
Mainly used in nuclear reactors and other no-fail applications, it comes in Analogue & Digital forms and here is the science according to Patol's website:
The cable is analogue LHDC is a coaxial cable constructed with a copper coated steel central conductor, an inner insulation (dielectric), a tinned copper braid layer and an overall protective sheath. Additional over sheaths are available for mechanical protection with Stainless Steel armour and nylon to provide resistance to Chemicals and Ultra Violet radiation.
The primary mechanism of heat (fire) detection is that the resistance of the dielectric is monitored between the central conductor and braid layer, which has a negative temperature coefficient (NTC).
Analogue cable is employed in conjunction with an end of line terminating device for continuity monitoring and a zone monitoring controller providing adjustable alarm thresholds and Fire and Fault outputs.
Digital LHDC operates at fixed temperatures and is non-resettable. The Digital LHDC comprises of a twisted pair, two core cable. Each core is a tinned copper coated spring steel conductor and has special heat reactive polymer insulation.
The cable has a protective chemical and UV resistant outer jacket / sheath. Additional mechanical protection is provided with optional Stainless Steel outer armour.
The Digital LHDC operates by reacting to heat (fire).
The insulators between the two conductors plasticizes at the design temperature creating a switch circuit at the point of operation.
The LHDC cable is employed in conjunction with an end of line terminating device for continuity monitoring and a zone monitoring controller to provide outputs for Fire and Fault. An LHDC controller with Distance Location (up to 2000m) to the point of operation is also available.
So there you have it - a cable that detects heat. For me it's amazing the very idea that cable will detect heat with no external sensors. Yet another example of a Great British designed and manufactured product!
Nick Locke, Nicab Ltd