Fiber Optic Linear Heat Detection

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A Linear Heat Detection (LHD) system is intended to monitor and identify temperature changes along a sensor cable’s length. A fiber optic LHD employs standard fiber optic sensor cables, usually spanning several kilometers, serving as linear temperature sensors. These systems are fully distributed, meaning they respond to heat at any point along the cable in the same manner. This leads to a continuous temperature profile across the entire length of the sensor cable.

Fiber optic Linear Heat Detection (LHD) systems are designed to monitor and identify temperature fluctuations along a sensor cable that can extend for several kilometers. By employing certified fiber optic LHD cables as continuous temperature detectors, this system is capable of responding to heat at any point along the cable, effectively identifying hotspots and fires with exceptional accuracy. For instance, across a distance of 10 km, the system is capable of measuring 10,000 temperature points every 5 seconds, allowing for swift detection and precise data regarding the location, size, and progression of a fire. By ensuring vigilant and ongoing temperature monitoring over large distances, fiber optic LHD significantly improves fire safety for various critical infrastructures, including traffic and utility tunnels, parking garages, conveyors, cable trays, solar farms, and battery storage facilities.

How Linear Heat Detection Works

A fiber optic Linear Heat Detection (LHD) system primarily comprises the interrogator unit and the sensor element, which is the fiber optic sensor cable. By employing a single optical fiber within the sensor cable, LHD enables real-time temperature measurements and monitoring of changes at every point along the entire length of the cable. It identifies hotspots and fires, activating fire alarm or suppression systems, while delivering accurate details about the location, size, temperature, and spread of the fire over distances of several kilometers.

How Linear Heat Detection Works

Enhance Temperature Control Using Raman Reflectometry

The LHD measurement technique relies on the Raman effect. A laser pulse generated by the LHD interrogator passes through a single optical fiber. As light interacts with the glass molecules, it scatters back to the sending end, conveying temperature data along the sensor’s path.

The temperature measurement is established by the time it takes for the light pulse to return (time of flight), similar to how radar echoes are analyzed. Using just one passive fiber optic cable, the temperature of a whole asset is continuously monitored.

Enhance Temperature Control Using Raman Reflectometry

Airway Security’s proprietary code correlation technology provides exceptional system reliability and precise measurements over extended distances, ensuring high spatial resolution and quick measurement intervals.

In contrast to traditional techniques that utilize individual optical pulses to gauge temperature distribution along the fiber, this approach utilizes specific sequences of pulses (codes) to inject considerably more probing energy into the fiber. This results in a significant enhancement of the Raman backscatter signal received by the detector, greatly enhancing the signal-to-noise ratio (SNR). Through mathematical deconvolution of the detector signal, the full spatial resolution is recovered, which is governed by the length of a single bit of the code instead of the entire code length.

How does Raman Reflectometry Work

Eager to learn more about how LHD, also known as Raman Reflectometry, works? What role does backscattering play, and how are temperature locations determined? Watch our video to find out more about the main work principles here.

Video: How does Raman Reflectometry Work?
Distributed Temperature Sensing

Benefits & Advantages of Linear Heat Detection

Linear Heat Detection offers many advantages for fire detection applications, including:

Extended Coverage Capabilities and Continuous Monitoring

A single fiber optic linear heat detection (LHD) cable can span long distances, removing the necessity for several sensors or multiple linear heat detectors, and offering a cost-effective solution that effectively oversees expansive spaces. Moreover, fiber optic LHD systems maintain uniformity throughout their entire length, guaranteeing dependable monitoring over wide areas.

Fiber optic LHD provides exceptional sensitivity and temperature resolution because it can detect temperature changes throughout the full length of the fiber. This capability enables a more precise and responsive monitoring solution compared to other thermal detection systems, which may struggle with identifying subtle temperature fluctuations, potentially resulting in delayed heat detection.

Linear Heat Detection systems identify and precisely locate temperature changes, hotspots, or fire incidents with spatial resolution accuracy of less than -0.5 meters (for example, AP Sensing’s LHD N45-Series). This technology offers swift and precise information regarding the position, magnitude, and progression of a fire, along with pre-alarms that can alert operators to potential issues in specific locations or areas, facilitating early intervention efforts to support rapid fire prevention or suppression.

Fiber optic LHD systems utilize fiber optic cables as sensors, providing immunity to electromagnetic interference. This makes the sensing solution effective in various harsh environments, such as those with dirt, dust, corrosion, humidity, extreme temperatures and fluctuations, radioactivity, and solvent vapors. Furthermore, LHD systems can be customized to meet different installation needs and typically integrate with current fire alarm systems to quickly activate alarms, trigger sprinkler systems, or alert relevant personnel.

Fiber optic LHD systems naturally require very little maintenance. Their remarkable reliability is attributed to the high quality of instruments like AP Sensing’s LHD N45 series, which boasts an annualized failure rate (AFR) of just 1%. Moreover, the fiber optic cables utilized are completely passive and built to last, ensuring dependable performance over an extended period. This benefit is especially crucial in hard-to-access or inaccessible locations, ensuring a long-term, maintenance-free operation.

In numerous fire detection systems, effective protection can be achieved by utilizing maximum thresholds, temperature gradients, or differences from the average. These parameters can be customized for each detection zone based on environmental conditions and anticipated critical thresholds to optimize suitability for specific application requirements. Fiber optic Linear Heat Detection facilitates intelligent alarm configuration with the capability of supporting up to 2,000 zones per sensor channel, which is particularly advantageous for extensive infrastructures, as the sensor cable often traverses various areas subjected to different temperature conditions. Read more here.

A Linear Heat Detection system consists of two main components: the sensor cable and the LHD interrogator. Depending on the setup, monitoring can still take place even if the sensor cable is compromised, such as from damage caused by construction activities or other accidental or intentional disruptions. For optimal system redundancy, various configurations of the sensor cable and interrogator can be implemented.

Use Cases of Linear Heat Detection

Fiber optic LHD systems are adaptable and provide exceptional reliability, even in challenging conditions. As a result, they are employed in various applications that require precise fire detection. These systems are especially advantageous in specialized hazard zones, where a fire can lead to catastrophic outcomes, jeopardizing human safety, damaging infrastructure, and resulting in extended downtimes.

Some of the key applications of Linear Heat Detection systems include:

Comparison of Linear Heat Detection Systems

Compared to other fire detection methods, fiber optic LHD offers many advantages. A fiber optic based LHD solution detects fires or hotspots quickly and precisely identifies their location within a few meters. In addition to the advantages mentioned above, the benefits of fiber optic LHD in direct comparison with conventional LHD systems (including analog, digital and multipoint LHD) are as follows:

Airway Security’s LHD system

LHD N45-Series

With the third generation of our LHD system, the N45-Series, Airway Security is raising the standard for fiber optic LHD. The N45-Series is certified to national and international standards for fire detection, offering the longest certified range on the market. No other fire detection system can withstand temperatures up to 750 °C (1400 °F) without losing monitoring capabilities.

Discover the LHD N45-Series
LHD N45 Series

Fiber Optic Sensor Cables

Our solution also includes certified, easy to install and maintenance-free sensor cables to fit your requirements. These completely passive cables are inherently safe against electromagnetic interference (EMI) and withstand operating temperature from – 40 up to +85 (150) °C.

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Fiber Optic Sensor Cables

Key Takeaways

Linear heat detection systems are a notable improvement in fire safety technology. By enabling continuous heat detection throughout the full length of a sensor cable, these systems deliver a degree of accuracy and dependability that conventional fire detection methods often lack. They can withstand harsh environments and resist electromagnetic interference, making them ideal for various applications. Additionally, with consistent testing and upkeep, these systems can provide many years of dependable performance.

Fire safety is an essential issue that requires serious focus. Thanks to technological progress, tools such as Linear Heat Detection systems offer considerable peace of mind. These systems mark a significant advancement and play a crucial role in fire safety.

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Airway Security, known for its reliable performance and ongoing innovation, provides a fully integrated, comprehensive solution crafted in Germany. Our team collaborates with you to choose the ideal combination of technologies that meet your needs.

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Distributed Temperature Sensing

Frequently Asked Questions

What Factors Influence the Response Time of a Linear Heat Detection system?

The measurement duration of an LHD system is solely dependent on the interrogator unit; however, the response time of a fiber optic linear heat detector is affected by various factors. These factors encompass the thermal characteristics of the sensor cable, the method of cable installation, alarm parameter settings, type of fire, heat release rate (HRR), and environmental conditions like wind speed. Notably, the thermal characteristics of the sensor cable are particularly significant as they largely dictate the overall system’s response behavior, contrary to the common misconception that it is primarily the measurement duration of the interrogator unit that influences this response.

Typically, a smaller spatial resolution leads to increased noise levels, while a broader spatial resolution smooths out the temperature trace and diminishes the statistical uncertainty of measurements, thereby enhancing temperature resolution and improving resilience against false alarms. In practical scenarios and actual fire events, a spatial resolution as low as one meter is usually adequate, with larger resolutions of two or four meters often being preferred.

The dependability of a fiber optic Linear Heat Detection (LHD) system can be enhanced not only through careful design, choice of components, and rigorous testing, but also by intelligent installation and operation of the system. This approach fosters fault tolerance in both individual components and the system as a whole.