MTL Barries - MTL7706 Analog Input (high level) 

The MTL7706 barrier works by limiting the energy (voltage and current) that passes into a hazardous area through a series of Zener diodes and a terminating resistor. In a fault condition, the Zener diodes redirect excess voltage to ground, while the resistor limits the current to a safe level, preventing ignition of a flammable atmosphere. A fuse provides an extra layer of protection for the diodes against overcurrent.

Key components and their function

• Zener diodes: Two stages of Zener diodes are used to clamp the voltage at a safe level. If one stage fails, the second stage still provides protection.
• Terminating resistor: This resistor limits the current that can pass through the barrier to a safe value.
• Fuse: A fuse protects the diodes from overcurrent and short circuits, adding a final layer of safety.

ANALOG INPUT - RANGE BARRIER APPLICATIONS

How it protects a hazardous area

• Energy limitation: The primary function is to limit the electrical energy transferred to a hazardous area to a level that is below the energy required to cause an ignition.
• Fault condition: In the event of a fault in the safe area (e.g., a short circuit or overvoltage), the Zener diodes and resistor work together to prevent the fault from causing a dangerous energy surge in the hazardous area.
• Safety by design: The two stages of Zener diodes ensure continued safety even if one stage fails

The MTL7706 is a passive intrinsically safe (IS) shunt-diode zener barrier that works by safely diverting excess electrical energy to the ground to prevent ignition in flammable atmospheres. This method of explosion prevention allows for the use of standard instrumentation and even live maintenance in hazardous areas.

Working Principle

The core principle of all MTL7700 series zener barriers is to limit the voltage and current that can enter a hazardous area from a safe area, even during an electrical fault. The MTL7706 achieves this using a combination of specific passive components:

• Zener Diodes: These are set up in two stages within each channel to limit the voltage. In the event of an electrical fault in the safe area, the diodes redirect any excess voltage safely to the earth (ground).
• Resistor: An "infallible" terminating resistor limits the current flow into the hazardous area.
• Fuse: A fuse is included to protect the zener diodes from current overload and short circuits, ensuring the safety mechanism remains intact.

The two stages of voltage limitation ensure continued safety even if one stage fails, making the device highly reliable. The entire assembly is designed to be a simple, robust, and passive device, meaning it does not actively regulate the output but rather acts as a safety "shunt" to ground for any dangerous energy levels.

Application

The MTL7706 is a single-channel barrier primarily used with "smart" 4-20mA transmitters and other compatible 2-wire transmitters approved for use in hazardous areas. It ensures that the energy supplied to the field device (in the hazardous area) remains below the ignition point of the surrounding atmosphere.
More details can be found in the product's official Eaton documentation.

 Full Datasheet