MTL Barries - MTL7767+ -  POSITIVE DC SYSTEMS (Low-level to 12V dc systems)

The MTL7767+ is an intrinsically safe (IS) shunt-diode barrier that prevents energy from passing into a hazardous area, limiting it to a level that cannot ignite flammable atmospheres. Its working principle is to use a network of diodes and resistors to clamp the voltage and current across the barrier to a safe level. The MTL7767+ specifically is a 2-channel, 15V barrier with a positive polarity, designed for 6V and 12V DC systems, and its channels can be safely combined in IIC gas applications.

How it works

• Energy limiting: The core of the barrier is a network of zener diodes and resistors. In a normal operating state, the barrier allows the signal to pass from the safe area to the hazardous area with minimal impact.
• Safety function: If a fault condition occurs, such as a short circuit or a power surge, the diodes and resistors are designed to clamp the voltage and current to a level below the ignition point of the surrounding flammable atmosphere.
• Shunt-diode barrier: This type of barrier is called a "shunt" barrier because it "shunts" or diverts excess energy to ground when a fault condition occurs, preventing it from reaching the hazardous area.

POSITIVE DC SYSTEMS (Low-level to 12V dc systems)

Key features of the MTL7767+

• Dual channel: It has two independent channels for two separate circuits.
• Voltage and polarity: It is a 15V barrier with a positive polarity, meaning it's suitable for positive DC systems and is designed for 6V and 12V DC applications.
• IIC gas classification: Its channels can be safely combined for use in IIC hazardous locations.
• Din-rail mounting: It mounts easily on a standard DIN rail, which is a common industrial mounting standard.
• Removable terminals: The terminals are removable for easier installation and maintenance.
• Bussed power feed: It can be used with a power bus (like the MTL7798) to share power and protection with other modules on the same rail, simplifying wiring.

The MTL7767+ is an intrinsically safe (IS) shunt-diode zener barrier designed to prevent explosions in hazardous areas by limiting the amount of energy that can enter those areas.

Working Principle

The core principle of the MTL7767+ is to ensure that the electrical energy (voltage and current) flowing into a hazardous environment remains below the level required to ignite flammable gases, vapors, or dust present in the atmosphere.
This is achieved through a simple, robust design utilizing three primary components connected between the safe and hazardous areas:

1. Zener Diodes: These are connected in a shunt configuration (parallel to the signal lines). Under normal operating conditions, the voltage is below the zener breakdown voltage, so the current flows through the circuit normally. However, in the event of a fault in the safe area that causes an overvoltage, the zener diodes conduct heavily. They "shunt" (divert) the excess voltage and current away from the hazardous area and to a high-integrity earth ground connection.
2. Series Resistors: Resistors are placed in series with the signal lines. They limit the current flowing into the hazardous area and also limit the current that the zener diodes have to handle during a fault condition.
3. Fuse: A fuse provides protection by blowing if the current reaches an unsafe level, permanently breaking the connection to the hazardous area in extreme fault scenarios.

By clamping the voltage and limiting the current, the barrier ensures that any potential spark in the hazardous area is too weak to cause an ignition.

Key Features and Operation

• Intrinsically Safe (IS) Technique: The barrier relies on the principle of preventing explosions rather than containing them.
• DIN-Rail Mounting: It clamps securely onto a standard T-section DIN rail, which simultaneously makes a reliable, low-resistance earth connection essential for the zener barrier to function correctly.
• Removable Terminals: This feature allows for easy installation, maintenance, and simple loop disconnection without rewiring.
• Live Maintenance: A major advantage of intrinsic safety systems is that maintenance and calibration can be performed on field devices in the hazardous area without having to power down the entire system or obtain "hot work" permits.

For technical specifications and circuit diagrams, you can refer to the official MTL7700 Range Datasheet from Eaton.

 Full Datasheet