Temperature Measurement


Continuous fire and overheat detection systems

May 2005 Temperature Measurement

The Fenwal continuous fire detection system is believed to be alone in its field, with the unique ability to detect specific overheat conditions at any point along the entire length of its sensing element run - without regard for rate of temperature rise or average ambient temperature.

This discrete sensing capability offers greater sensitivity and response than systems relying on the 'averaging' technique. It is the only system designed with a single control, which has the capability of connecting elements set at a variety of temperatures to provide simultaneous coverage for different alarm points in the several areas being protected.

The discrete sensing element is a slender Inconel tube, packed with thermally sensitive eutectic salt and nickel wire centre conductor. Lengths of these sensing elements are connected in series to a control unit. The elements may be of equal or varying length and of the same or different temperature settings.

The control unit, which operates directly from the power source, presents a small voltage to the sensing elements. When an overheat condition occurs at any point along the element length, the resistance of the eutectic salt within the sensing element drops sharply, which in turn causes the current to flow between the outer sheath and the centre conductor. This current flow is sensed by the control unit, which produces a signal to actuate the output relay. When the fire has been extinguished or the critical temperature has been lowered, the Fenwal CFD System automatically returns to standby alert, ready to detect any subsequent fire or overheat condition. This system may be wired to employ a 'loop' circuit. In this case, should an open circuit occur, the system will still signal fire or overheat. If multiple open circuits occur, only the section between breaks becomes inoperative.

For more information contact Andy Brown, Temperature Controls, 011 791 6000, [email protected], www.tempcon.co.za



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