Fiber Optic Linear Heat Detection

A single fiber optic LHD cable can cover long distances, eliminating the need for multiple sensors or multiple linear heat detectors, and providing a cost-effective solution that efficiently monitors large areas. Additionally, fiber optic LHD systems, remain consistent over the entire length, ensuring reliable monitoring across extended areas.

Fiber optic LHD offers precise sensitivity and temperature resolution due to its ability to measure temperature changes along the entire length of the fiber. This sensing capability allows for more accurate and responsive monitoring solution than other thermal detection systems which may have limitations in detecting subtle temperature variations, potentially leading to delayed heat detection.

Linear Heat Detection systems locate and pinpoint the exact location of temperature changes, hotspots, or fire events down to below -0.5 meter spatial resolution (e.g. AP Sensing’s LHD N45-Series). This provides accurate and quick information on the location, size, and spread of a fire, with pre-alarms, which can give operators early indication of upcoming problems at specific locations or areas, and early intervention measures aiding in rapid responses for fire prevention or suppression.

Fiber optic LHD systems use fiber optic cables as a sensors, which are immune to electromagnetic interference. This makes the sensing solution suitable for a wide range of harsh surroundings including dirt, dust, corrosion, humidity, extreme temperatures and temperature changes, radioactivity and solvent vapors. Additionally, LHD systems are adaptable to varying installation requirements and usually integrate with existing fire alarm systems to immediately trigger alarms, activate trigger sprinkler systems, or send notifications to relevant personnel.

Fiber optic LHD systems inherently require minimal maintenance. Exceptionally high reliability is ensured thanks to the outstanding quality of the instruments, such as AP Sensing's LHD N45 series with an annualized failure rate (AFR) of only 1%. In addition, the fiber optic cables used are purely passive and durable, with a long lifetime, ensuring reliable performance over time. This is particularly invaluable for areas difficult or impossible to reach, providing a guarantee of long-term, maintenance-free operation.

In many fire detection applications, reliable protection can be enabled with maximum thresholds, temperature gradients or temperature differences to average. Depending on the environmental conditions and the expected critical thresholds, these parameters can be set and tweaked individually per detection zone to reach maximum fit for the application needs. Fiber optic Linear Heat Detection allows smart alarm configuration with up to 2,000 zones per sensor channel, which is beneficial especially for large-scale infrastructures, where the sensor cable typically runs through different areas under various temperature conditions. Read more here

A Linear Heat Detection system comprises two elements, the sensor cable and the LHD interrogator. Depending on the configuration, monitoring can continue even in the case of a break of the sensor cable, e.g. due to damage from construction works or other accidential or deliberate interference. For highest requirements on system redundancy, different configurations of the sensor cable and interrogator are possible.

While the measurement time of an LHD system is exclusively a parameter of the interrogator unit, the response time of a fiber optic linear heat detector is determined and influenced by a multitude of parameters. These include the thermal behavior of the sensor cable, the cable installation method, the alarm parameter configuration, the fire type, the heat release rate (HRR) and environmental conditions such as wind speed. The thermal behavior of the sensor cable plays a special role here since it determines the response behavior of the overall system to a predominant extent and not—as is often erroneously assumed—the measurement time of the interrogator unit.

A smaller spatial resolution typically results in higher noise levels, while a wider spatial resolution smoothens a temperature trace and reduces statistical uncertainty of measurements, hence improving the temperature resolution and consequently false alarm resilience. Considering the real world and real fire situations, normally a spatial resolution as low as one meter is more than sufficient, often a larger resolution of two or even four meters is preferential.

The reliability of a fiber optic Linear Heat Detection (LHD) system can be positively influenced not only by design, component selection, and intensive testing, but also by clever setup and use of the system itself. In this way, fault resilience is achieved in both system components as well as the overall system.