The MTL7728+ is an intrinsically safe, zone-powered Zener-diode barrier designed for use in conventional fire detection systems within hazardous areas. It ensures that hazardous zones are protected from overvoltage and overcurrent conditions, providing reliable safety in potentially explosive environments.
Each zone incorporates 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 restrict the voltage entering the hazardous area, while the resistor limits the current. A dedicated fuse safeguards the diodes, and the dual voltage-limiting stages maintain protection even if one stage fails. No active current-limiting circuits are used, ensuring fail-safe operation.
The MTL7728+ is certified ‘ia’ for all zones and ‘IIC’ for all explosive atmospheres, making it suitable for the most stringent hazardous area applications.
Part of the MTL7700 Series, these intrinsically safe shunt-diode safety barriers feature high packing density, simplified installation, and easy connection, commissioning, and maintenance. Each barrier includes a secondary replaceable fuse, which protects the internal safety fuse during commissioning or fault-finding. These fuses are housed in small mouldings that can be latched in a disconnect position to isolate safe and hazardous areas without additional disconnect terminals.
Key Features
Removable, colour-coded terminals for easy wiring
Bussed power feed to other modules
Relay and solid-state switch modules compatible
Dual channel variants: 6.3 mm per channel
Proximity detector inputs supported
Standardised terminal numbering and safety descriptions
Dimensions: 105 × 90 × 12.6 mm
Number of Channels: 1
Supply Voltage: 28 V DC
Maximum Safety Voltage: 26 V DC
Safety Current Resistance: 300 Ω
Maximum Safety Current: 93 mA
Signal Type: Analogue
Operating Temperature Range: –20°C to +65°C
Hazardous Area Certification: ATEX
This design combines robust intrinsic safety, high reliability, and ease of installation, making the MTL7728+ ideal for conventional fire detection in hazardous environments.