MTL Barrier  - MTL787S+ SHUNT DIODE SAFETY BARRIER

The MTL787S+ is an Intrinsically Safe (IS) shunt-diode safety barrier that works by passively limiting energy (voltage, current) from the safe area to the hazardous area using Zener diodes, resistors, and fuses, preventing sparks that could ignite explosive atmospheres. It's a simple, reliable device for connecting instruments like transmitters, switches, or thermocouples, featuring self-checking earthing for safety, and operates without needing external power, making it a worldwide standard for process automation safety.

Core Working Principle:

1. Energy Limiting: The barrier sits in series with the signal line, using a combination of Zener diodes (to clamp voltage) and resistors (to limit current) to restrict the electrical energy that can reach the hazardous area.
2. Fuse Protection: A fuse is included to protect the diodes from excessive fault currents that could otherwise blow them and compromise safety.
3. Two-Stage Safety: This diode/resistor/fuse arrangement provides two stages of protection, ensuring safety even if one stage fails.
4. Passive Operation: It's a passive device, meaning it doesn't require its own power supply; it uses the signal from the safe area to function.
5. Earth Connection: It relies on a direct, self-checking earth connection to a busbar for ultimate safety, ensuring fault currents are shunted away.

MTL787S+ SHUNT DIODE SAFETY BARRIER

How it Achieves Intrinsic Safety:

• Prevents Ignition: By clamping voltage and limiting current, it ensures the electrical energy in the hazardous area stays below the minimum ignition energy (MIE) of any flammable gas or dust.
• Works with Simple Devices: Ideal for "simple" devices (thermocouples, switches) or certified apparatus (transmitters, sensors) in hazardous zones.
• Reliable & Standard: Known for quality and reliability, it's a fundamental technique in process control for safe operations in explosive environments.

In essence, the MTL787S+ acts as a fundamental safety gate, allowing signals to pass but strictly controlling the energy flow to prevent explosions.

The MTL787S+ is an intrinsically safe shunt-diode (Zener) safety barrier. Its primary purpose is to limit the electrical energy transferred from a "safe area" (control room) to a "hazardous area" (explosive atmosphere) to prevent ignition.

Core Working Principle

The device operates on three fundamental electronic stages designed for passive energy limitation:

• Voltage Limitation (Zener Diodes): Under normal conditions, the Zener diodes do not conduct, allowing signals to pass freely. If an overvoltage fault occurs in the safe area, the diodes reach their breakdown voltage and begin to conduct, "shunting" (diverting) the excess voltage to a high-integrity earth ground.
• Current Limitation (Infallible Resistor): A series resistor is placed on the hazardous-area side to limit the maximum current that can reach the field equipment under any fault condition.
• Fault Protection (Safety Fuse): If the safe-area voltage exceeds the barrier's rating for a prolonged period, the resulting high current through the Zener diodes will blow the internal fuse, permanently disconnecting the circuit to maintain safety.

Key Specifications & Features

• Intrinsically Safe (IS): Certified for use in Zone 0, 1, and 2 hazardous areas (Group IIC gas classification).
• Passive Protection: It does not require a separate power supply to function as a barrier.
• High-Integrity Earthing: Critical to its operation is a reliable IS Earth connection, typically made via the mounting busbar or DIN rail.
• Applications: Typically used for digital inputs, solenoid valves, and transmitters where a specific safety description (Voltage/Resistance) is required.

For more technical details, refer to the MTL700 Series Datasheet.

 Full Datasheet

 Manual