Function of Linear Temperature Sensing Cable Terminal Box

A Linear Temperature Sensing Cable Terminal Box connects and monitors linear heat detection cables, enabling early fire or overheating detection by transmitting signals when the cable senses abnormal temperature rises.

Working Principle of Linear Heat Detection Cables

Linear heat detection (LHD) cables are continuous heat sensors that detect temperature changes along their entire length . They consist of two conductors insulated with a heat-sensitive polymer, often wrapped with protective layers. There are two main types:

• Digital (fixed temperature, non-resettable): The insulation melts at a specific temperature, allowing the conductors to make contact and trigger an alarm . Once activated, the cable section must be replaced.
• Analogue (resettable): The insulation's resistance changes proportionally with temperature. The system monitors these changes and triggers an alarm if a preset threshold is exceeded. After cooling, the cable can reset . These cables are ideal for areas where conventional point detectors are impractical, such as tunnels, cable trays, or industrial plants .

Role of the Terminal Box

The terminal box serves as the interface between the LHD cable and the fire control system . Its main functions include:

1. Connection and Continuity Monitoring: Incoming and outgoing cables are connected to terminals inside the box, ensuring proper polarity and continuity. End-of-line (EOL) devices are often used to monitor the integrity of the cable circuit .
2. Signal Transmission: When the cable detects a temperature rise, the terminal box transmits the alarm signal to the control panel or fire alarm system.
3. Mechanical Support: The terminal box secures the cable and printed circuit board (PCB), preventing kinks or damage that could affect performance .
4. Integration with Controllers: For analogue systems, the terminal box may interface with modulators or controllers that interpret resistance changes and trigger alarms or fault outputs .

Installation Considerations

• The cable should be loosely secured to avoid kinks or compression that could affect sensitivity .
• Terminal boxes must be mounted securely, with proper screw fixation through the PCB and box to the surface.
• Correct polarity and cable routing are essential to ensure reliable operation and accurate detection .

Summary

The linear temperature sensing cable terminal box is a critical component in LHD systems. It ensures proper connection, monitors cable continuity, and transmits alarm signals when abnormal temperatures are detected. By combining heat-sensitive cables with terminal boxes, LHD systems provide continuous, reliable, and early detection of fire or overheating in complex or hard-to-access environments .