ZENER BARIERS MTL7787+
LIMITS / VOLTAGE CURRENT INTO HAZARDOUS AREA IN THE EVENT OF A FAULT IN THE SAFE AREA 2 STAGES OF VOLTAGE LIMITATION IS APPROVED 12.5mm WIDE
The 7787+ barrier 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 employed. The MTL7787+ is certified ‘ia’ for all zones and ‘IIC’ for all explosive atmospheres.
The recommended barrier for use with ‘conventional’ and ‘smart’ (4 to 20) mA transmitters (fed by a 26 V regulated supply) is the MTL7787+. This provides up to 12.9 V at Vwkg and 20 mA for a transmitter and its lines as well as 5 V for the typical 250Ω load.