Model MTL7728+ is an intrinsically safe, zone-powered, Zener-diode barrier for use in
conventional fire detection systems for protection within hazardous areas.
Each Zone contains two stages of pulse-tested Zener or forward- connected diodes and
an ‘infallible’ terminating resistor. In the event of an electrical fault in the safe area, the
diodes limit the voltage that can reach the hazardous area and the resistor limits the
current. A fuse protects the diodes, and the two stages of voltage limitation ensure
continued safety if either stage should fail. No active output-current limiting circuits are
Model MTL7728+ is certified ‘ia’ for all zones and ‘IIC’ for all explosive atmospheres.