|Tipo dei prodotti:||Heat detection (it)|
DETECT-A-FIRE units are designed with RATE COMPENSATION. DAF unit accurately senses the surrounding air temperature regardless of the fire growth rate. At precisely the predetermined danger point, the system is activated. Fixed temperature detectors must be completely heated to alarm temperature and therefore a disastrous lag in time may occur with a fast rate fire. Rate-of-rise devices, on the other hand, are triggered by the rate of increase in ambient temperature and are subject to false alarm caused by harmless, transient thermal gradients such as rush of warm air from process ovens. The outer shell of DAF (figure 1) is made of a rapidly expanding alloy which closely follows changes in surrounding air temperature. The inner struts are made of a lower expanding alloy. Designed to resist thermal energy absorption and sealed inside the shell, the struts follow temperature changes more slowly. A slow rate fire (figure 2) will heat the shell and struts together. At the "set point", the unit will trigger, actuating the alarm. A transient rush of warm air up to 40 F7min. may expand the shell, but not enough to trigger the unit. By ignoring transient warm air excursion, the DAF unit virtually eliminates false alarms prevalent with rate-ofrise devices. If a fast rate fire (figure 3) starts, the shell will expand rapidly. The struts will close, actuating the alarm. The faster the fire rate of growth, the sooner the DAF units will react.