The principle of operation of temperature sensor detectors mainly relies on the use of thermosensitive components to detect fires. In the initial stages of a fire, large amounts of smoke are generated, and materials release significant amounts of heat during combustion, causing a rapid increase in ambient temperature. The thermosensitive components in the detector undergo physical changes, converting temperature signals into electrical signals, which are then processed for alarm purposes. Below, Siemens fire alarm manufacturers will specifically explain:

　　There are various types of heat detectors, which can be classified into fixed temperature, rate-of-rise, and combination fixed-temperature/rate-of-rise detectors based on their thermal sensitivity and structural types. In the design of electronic combination detectors, two thermistors with similar performance are generally used. One is placed inside a metal shield, while the other is placed externally. The external thermistor has a faster response speed, while the internal one has a slower response due to thermal insulation. The temperature difference between them is utilized to achieve rate-of-rise alarm, while the external thermistor is set at a fixed temperature (62°C for level 1 sensitivity, 70°C for level 2 sensitivity, and 78°C for level 3 sensitivity) to achieve fixed-temperature alarm. Apart from signal acquisition and amplification, the other components of the circuit are essentially the same as those of ionization smoke detectors.

　　According to the principle of operation of temperature sensor detectors, they can be divided into three categories:

　　1. Fixed temperature detectors: These detectors trigger an alarm when the temperature rise caused by a fire exceeds a certain fixed value within a specified time. They come in linear and point structures. In linear detectors, the insulation material melts when the local ambient temperature reaches a specified value, causing the two conductors to short circuit and generate a fire alarm signal. Point-type fixed temperature detectors utilize components such as bimetallic strips, fusible metals, thermocouples, and thermosensitive semiconductor resistors to generate fire alarm signals at specified temperature values.

　　2. Rate-of-rise detectors: These detectors trigger an alarm when the rate of temperature rise caused by a fire exceeds a certain specified value within a specified time. They also come in linear and point structures. Linear rate-of-rise detectors operate based on the widespread thermal effect, while point-type detectors operate based on local thermal effects. The main sensing devices are air chambers and thermosensitive semiconductor resistor elements.

　　3. Combination fixed-temperature/rate-of-rise detectors: These detectors combine the principles of fixed temperature and rate-of-rise detection and integrate both detector structures. They are generally point-type combination detectors, such as membrane box or thermosensitive semiconductor resistor-type detectors.

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