Linear Heat Detection (LHD) (also known as Linear Detection Wire or Linear Heat Detection Cable or Linear Heat) is a very commonly used method of fire detection. It can detect a fire anywhere along the length of the cable, and can be of lengths in excess of a kilometer.
Linear Heat Detection (LHD) is a line-type form of fixed temperature heat detection used in common commercial and industrial environments. This linear cable can detect a fire anywhere along its entire length and is available in multiple temperatures.
Linear Heat Detection (LHD) cable is essentially a two-core cable terminated by an end-of-line resistor (resistance varies with application). The two cores are separated by a polymer plastic, that is designed to melt at a specific temperature (commonly 68 °C for building applications), and without which causes the two cores to short. This can be seen as a change in resistance in the wire.
Linear Heat Detection Cable

Digital linear heat detection (LHD) cable is a combination of advanced polymer and digital technologies that can detect heat anywhere along its entire length. LHD cable is also compatible with any listed addressable or conventional panel. For addressable panels use addressable contact monitor modules. At the core of SafeCable is a twisted pair of extremely low resistance trimetallic conductors, sheathed in new advanced thermal polymers. These polymers are chemically engineered to break down at specific fixed temperatures allowing the twisted conductors to make contact and initiate an alarm at the control panel without any calibration for changes in the ambient temperature. The distance locating module (DLM-Z2) has One or Two Zones, which can be cross-zoned, built-in. It also allows you to identify and display the location, in feet or meters from the panel, where heat was detected.

There are limited states the LHD cable can be in:
1. Open-circuit – Effectively an infinite resistance
2. Normal Operating Condition – Apparent resistance will be the same as the end-of-line resistor
3. Fire Detection – Resistance of the Linear Heat Cable to the short circuit

The linear heat detectors shall sense an overheat condition at any point along its length and pinpoint its location. The heat detection system shall comprise a heat sensing cable and a monitoring /control unit.
A change in temperature along the sensing cable shall cause a relative change in resistance of the cable. This change shall be detected by the monitoring /control unit which shall signal an alarm at the preset temperature.

The sensing cable may be multicore l. One end shall be connected to the monitoring unit. The other end shall be terminated so as to create a loop which shall be continuously monitored for open and short circuit fault, and alarm condition.
Selection Criteria for Linear Heat Detector.

Following are some minimum requirement applicable for linear heat detector, however requirements vary from industry to industry.
The outer jacket shall be made of material that resists corrosion, chemicals, moisture etc.

The linear heat detector cable and monitoring system shall be suitable for operation on a nominal 24V DC supply.
The alarm condition shall be latched at the control unit, with reset facility from the Fire and Gas panel, and locally on the control unit.
The unit shall provide outputs for fault and alarm conditions that are compatible with the main Fire and Gas panel.
Sensing cable and any termination units required shall be certified for use as part of an IS circuit when installed in hazardous area.
Sensing cable and any termination units required shall be certified for use as part of an IS circuit when installed in hazardous area.

Benefits of liner heat detection
There are many benefits to LHD. One of which is a continuous source of heat detection up to 10,000 feet. LHD cables are also very durable and long-lasting. Conversely, spot heat detectors do not offer the continuous field of detection of LHD cables, they don’t hold up very well, and can be easily damaged.

Fike, one of the many manufacturers of linear heat detectors, notes many benefits of LHD. Some of these benefits pertaining to their detector called Protectowire include:

Fewer false alarms and false suppressant discharge with Confirmed Temperature Intiation (CTI).
Detection device works with fire alarm system interface and modules that identify source and temperature of hazard
Easy installation and maintenance
Provides hazard coverage at every point on the cable for maximum protection
Available in a variety of lengths, cable coatings and alarm temperatures for maximum flexibility
Wide zone area, up to 10,000 feet of continuous detection
Common applications

LHD is ideal for areas where electronics may not be the best choice. These devices are particularly appropriate for areas where installation or maintenance access is in a physically demanding or hazardous area. LHD is also perfect for when fire detection is required in close proximity. For example, in closed-in areas where it’s easier to run a cable than place a thermostat.

Some of the most applications for LHD include:
APPLICATION
Freezers
Printing presses
Vehicle suppression systems
Warehouses
Oil and Gas
Coal Storage
High Temperature Vessels
Fuel Storage
Conveyor System
Cable Tray
Tunnels
High Speed Train
Transformers
Production machine
Critical facilities, etc.
Installation, testing, and maintenance

LHD cables should be installed by a licensed fire protection professional. Linear heat detectors are easy to maintain and require little to maintenance making them the perfect heat detection solution for many building owners.

There are many guidelines and parameters as set by NFPA regarding the installation, testing, and overall maintenance of LHD devices. A licensed professional will follow this protocol for installation which include testing the continuity of the linear heat detector with an ohm meter to ensure it is in proper working order.

Fire Systems Inc. has experienced fire protection technicians who are specifically trained in Linear Heat Detection. We will ensure the proper installation of your linear heat detector and keep you on track with scheduled testing and maintenance. Contact us today to find out if LHD is the best choice for your facility. Visit our website or call us at 080-383-68255 for more information.

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Fuel Storage Temperature Monitoring System

Petroleum storage tanks and cryogenic product storage facilities (liquid natural gas, LPG, ethylene, ammonia, etc.) require sensitive temperature monitoring systems to give ample warning of elevated temperatures prior to combustion. By providing an advanced notice of rising temperatures, appropriate steps can be taken to prevent a disaster from happening. Senkox TDS-FS Temperature Monitoring System is the ideal solution to fill this role. The TDS-FS system is composed of multiple Senkox HSD Linear Hot Spot Detectors and accessories; the HSD Linear Hot Spot Detector includes HSD linear heat sensors and DAQ modules.

The flexibility of the Senkox HSD Linear Heat Sensor cables, allows it to be mounted around the tank. The system provides real-time temperature monitoring and also detects the precise location of hot spots. As a result, safety personnel have real-time data of the thermal conditions of the storage tanks. This feature provides advanced warning and extra time for working personnel to deal with cases of overheating. It also clearly identifies the hot spot location.

Floating roof tanks are vulnerable to elevated temperatures due to the highly abrasive environment and presence of flammable gases. HSD Linear Hot Spot Detectors are most likely to occur near the secondary seal of a floating roof tank, as these are the areas that suffer most from high abrasion and the presence of flammable gases. The HSD sensors are installed along the secondary seal of the floating roof tank to provide real-time data regarding temperature changes.

Spherical storage tanks are commonly located in areas of high fire risk. HSD sensors are installed on the surface of the sphere, allowing continuous temperature monitoring. Detection of any hot spots will trigger location specific sprinkler systems.

Technical Advantages
Sensors are intrinsically safe, and can be installed in hazardous locations.
Continuous and flexible linear sensor provides superior coverage in tight spaces.
Continuous temperature monitoring and rapid response to changes in temperature.
Sensors are able to withstand high temperature and can be reused repeatedly.
Simple system layout with easy installation, low maintenance.
Detects the hot spot temperature in real-time.
Details the position and size of any hot spot.
Provides rate of temperature change (ROTC).


Specification
Sensor HSD Linear heat sensor
Sensor Type TLA, TLB, TLF, TPLA
Working Temperature -40 to 260 degrees C (Sensor)
Environmental
(Control Panel) Operating temperature range: -20 to 70 degrees C Relative humidity: 0 to 95%, non-condensing
Protection Degree Sensor: IP68; Control Panel: IP65.
Sensor Channels Up to 24
Communication Interface RS 485 Port, Modbus/RTU Protocol
Power Supply 12 to 35V DC, 10W max
Hazardous Location Sensor: Class I, Division 1
Control Panel: Class I, Division 2

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