Detect-A-Fire (DAF) units are designed with rate-of-rise compensation technology, which is influenced by the rate of heat rise (thermal gradient compensation). This provides a unique advantage over the two standard types of point temperature (heat) detectors; Fixed Temperature Detection and Rate-of-rise Detection. DAF units detect the temperature of the surrounding air independently of the rate of expansion of the fire and through thermal gradient compensation technology, the system alarms precisely at the predetermined danger point.

The secret of the sensitivity of the DAF (Fenwal) detectors lies in the design of the outer sheath, which is composed of a special alloy coating that facilitates rapid expansion of the element, thus allowing continuous monitoring of the ambient temperature variation around it. The inner core is made up of slower expanding alloy struts (cross members) designed to resist the absorption of thermal energy, which are sealed inside the sheath, these inner struts (cross members) follow the temperature changes more slowly. A slow expansion of the fire causes the outer sheath and inner braces (cross members) to heat up together, i.e. all the sensors that make up the element, so that the unit will alarm at a certain level of heat (pre-set sensor temperature). An airflow with a transient temperature of 40°F (4.4°C) per minute may expand the sheath but is not enough to trigger the alarm. By ignoring these limits of transient hot air variations, the DAF unit virtually eliminates much of the false alarms prevalent in thermal gradient detectors.

In the event of a rapid temperature rise, it will result in the rapid expansion of the outer sheath which will cause the braces (cross members) forming the inner core to close, thus activating the alarm contact. The higher the rate of heat rise (fire), the faster the sensor will react.

Fenwal Point Temperature Detector Product Sheet:


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