MTL Barries - MTL7761ac - STRAIN-GAUGE BRIDGES - 4-wire RTD's

The MTL7761AC is a zener barrier that uses a passive network of zener diodes, resistors, and fuses to prevent sparks and overheating in hazardous areas. It works by diverting excess electrical energy to ground, limiting the voltage and current that can pass into the hazardous area. This process keeps the energy below the level required to ignite flammable gases, making it safe for use in control and instrumentation systems.

How it works

• Safety components: Each channel in the barrier contains a series of pulse-tested zener diodes, a terminating resistor, and a fuse.
• Voltage limitation: In the event of an electrical fault in the safe area, the zener diodes limit the voltage that can reach the hazardous area to a safe level.
• Current limitation: The terminating resistor limits the current to prevent overheating and sparking.
• Redundant safety: The use of two stages of voltage limitation ensures continued safety even if one stage fails.
• Energy diversion: Any excess electrical energy is safely diverted to ground through the barrier.

STRAIN-GAUGE BRIDGES

4-wire RTD's

Key features

• Intrinsic safety: It enhances safety in hazardous areas by preventing sparks and overheating.
• Passive operation: It is a passive device and does not require a power supply for its safety function.
• High packing density: It provides a high channel count in a compact DIN-rail mountable design.
• Easy installation: It features removable terminals and angled wire entry for convenient installation and maintenance.

The MTL7761AC is a passive shunt-diode safety barrier that operates on the principle of intrinsic safety (IS) to protect equipment in hazardous areas by limiting electrical and thermal energy.

Working Principle

The primary function of the MTL7761AC is to prevent the ignition of flammable atmospheres by ensuring that the electrical energy transferred from a safe area to a hazardous area remains below a critical level. This is achieved using a simple, robust internal circuit:

• Zener Diodes: The barrier contains two stages of pulse-tested Zener diodes. In the event of an electrical fault or overvoltage in the safe area, the diodes conduct, diverting the excess voltage to a reliable earth ground.
• Resistors: An "infallible" terminating resistor is included in the circuit to limit the current that can flow into the hazardous area.
• Fuse: A fuse is incorporated to protect the diodes from excessive current, and the two stages of voltage limitation act as a fail-safe mechanism, ensuring continued safety even if one stage fails.

Function

The barrier limits both the voltage and current to intrinsically safe levels, preventing sparking or overheating that could cause an explosion in the presence of flammable materials.

Key Features

• Intrinsic Safety: Designed to meet high safety standards (certified 'ia' for all zones and 'IIC' for all explosive atmospheres).
• Passive Design: It relies on simple, reliable passive components (diodes, resistors, fuses) rather than active electronics for protection.
• DIN-Rail Mounting: The module securely clamps onto a standard T-section DIN rail, which simultaneously makes the essential intrinsic safety earth connection.
• Removable Terminals: Terminals can be unplugged to easily disconnect the loop for maintenance or testing.

Applications

The MTL7761AC is a 2-channel barrier suitable for applications such as connecting strain gauges and other passive instruments located within a hazardous area to control equipment in a safe area.

 Full Datasheet