MTL MEASUREMENT TECHNOLOGY SHUNT DIODE SAFETY BARRIER MTL 728-

MTL MEASUREMENT TECHNOLOGY SHUNT DIODE SAFETY BARRIER MTL 728-

The MTL 728+ is a robust, high-performance shunt diode safety barrier designed by MTL Measurement Technology to provide intrinsic safety (IS) protection for instrumentation and control loops in hazardous areas. It is a fundamental component for ensuring safety and preventing ignition risks in industries such as oil and gas, chemical, pharmaceutical, and petrochemical processing.

Core Function and Purpose

The primary purpose of the MTL 728+ is to limit the energy (voltage and current) that can be transferred from the safe area (control room) to the hazardous area (field). In the event of a fault in the safe-area equipment, the barrier prevents sufficient energy from reaching the hazardous area, thereby ensuring that any electrical sparks or thermal effects are too weak to ignite a potentially explosive atmosphere.

Key Features and Benefits

• Advanced Shunt-Diode Technology: Utilizes fast-acting zener diodes to clamp overvoltages and a series resistor to limit current, providing a reliable and maintenance-free method of protection.

• Wide Range of Models: The 728+ series covers a comprehensive selection of barriers for various signal types, including:

  • Analog I/O (4-20mA signals)

  • Discrete (Switch/Digital) inputs and outputs

  • Thermocouples (mV), RTDs (Pt100), and Frequency inputs

• High-Density DIN-Rail Mounting: Features a compact, modular design that allows for high-density installation on standard DIN-rails, saving valuable space in control panels and marshalling cabinets.

• Robust Galvanic Isolation: Many models offer galvanic isolation between the hazardous and safe areas. This prevents ground loops, isolates common-mode voltages, and protects connected equipment from damage due to potential differences.

• Comprehensive Certification: The series is globally certified to ATEX, IECEx, and other major international standards for intrinsic safety, ensuring compliance for worldwide use.

• “Plus” Enhancements: The “+” designation signifies improvements over the previous MTL 728 series, including enhanced performance specifications, broader temperature ratings, and updated certifications for modern industrial requirements.

• Clear Visual Indication: Features an LED indicator on each channel (on most models) to provide immediate visual confirmation of field-side loop health and power status, aiding in quick diagnostics and troubleshooting.

• Proven MTL Reliability: Built to the stringent quality standards of the MTL brand, known for its long-term reliability and performance in the most demanding industrial environments.

Typical Applications

The MTL 728+ barriers are used to protect a wide variety of field devices located in hazardous areas (Zones 0, 1, 2 / Div 1 & 2), such as:

• Pressure, Level, and Flow Transmitters

• Temperature Sensors (RTDs and Thermocouples)

• Solenoid Valves and Actuators

• Proximity Switches and Limit Switches

• Weighing Systems and Analytical Instruments

How It Works (Simplified)

1. Normal Operation: Under normal conditions, the 4-20mA signal (or other signal) passes through the barrier with minimal effect.

2. Overvoltage Fault: If a dangerous high voltage is accidentally applied to the safe-area terminals, the zener diodes instantly “clamp” the voltage to a safe level.

3. Overcurrent Fault: The series resistor limits the current that can flow to the hazardous area. The excess current is safely diverted to ground via the activated zener diodes.

4. Ground Connection: A high-integrity, low-resistance earth ground connection is critical for the shunt diodes to function correctly. This connection provides the path for fault currents.