Sperosens, in partnership with AP Sensing, recently launched its first fibre optic linear heat detection (LHD) system in South Africa.
Principle of operation
Distributed temperature sensing (DTS) utilises laser light and fibre optic cables to measure temperature. An infrared laser pulse is transmitted through the fibre with the incident energy being back-scattered from the glass molecules over the entire length. These minute light signals contain information about the temperature of the glass at any given point in the fibre, in accordance with the Raman Effect. The back scattered light is measured and then analysed for temperature. The position of the temperature reading along the length of the fibre is determined by measuring the time delay of the returning light pulse, similar to a radar echo.
Up to 10 km of fibre optic cable can be used, with the heat in each 1 metre section measured to an accuracy of °C accuracy. This enables users to monitor 10 000 temperature readings from one central point using one 10 km cable. DTS can monitor temperature under harsh conditions and over long distances to optimise maintenance, detect fires and overheating, and monitor environmental temperature.
AP Sensing’s linear heat series minimises operational costs and performs extremely reliably using a standard fibre optic cable which has no active components or electronic sensors within the exposed zone. Such cable is also immune to electromagnetic interference. Depending on cable grade, it can also be directly exposed to flames while still measuring accurately. Fire fighting effectiveness can hence be monitored throughout a fire event.
Applications include temperature monitoring along conveyor belts, inside sub-stations, switchgear cubicles and MCC rooms, inside coal bunkers, inside power cables, in mining tunnels and on cable racks plus many more. The benefits are accuracy, ease of installation, immunity to EMC, dirt, dust and humidity, and very little maintenance over an exceptionally long lifetime. The solution integrates easily into existing scada systems through dry contacts and/or communicating directly over Ethernet (TCP/IP) using standard protocols.
A practical example
One of the most famous applications of the LHD in Europe is the Eurotunnel fire monitoring system which activates and controls the suppression system. The Channel Tunnel is 38 km long and connects the UK with France. After experiencing a devastating fire in September 2008 the safety requirements were reviewed. Full-scale qualification tests were carried out in Germany under live fire conditions with intense temperatures from 5 MW fire loads, the equivalent of a fire involving 40 cars. The results were extremely convincing, resulting in full UL and FM approvals.
The system offers many benefits including fast activation and good control, which allows easy access for rescue services and enables effective fire fighting. AP Sensing’s system was installed as the fire monitoring system of choice, taking road and rail tunnel safety to a new level.
For more information contact Marihette Hattingh, Sperosens, 0861 773 767, [email protected], www.spero.co.za
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| www: | www.spero.co.za |
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