MTL 8937-HN

Description

Product Overview and Description

The MTL 8937-HN is a critical safety interface device from MTL (Measurement Technology Ltd), a world leader in hazardous area protection and industrial connectivity. This product is a high-density, multi-channel, modular safety barrier designed for installation in safe areas to provide intrinsically safe (IS) interfaces for field-mounted instruments located in hazardous (explosive) areas. Its primary function is to limit the energy (voltage and current) that can reach the hazardous area, thereby preventing the possibility of ignition from electrical sparks or thermal effects. The MTL 8937-HN is part of MTL’s extensive 8000 series of modular DIN-rail mounted barriers, offering a flexible and space-efficient solution for protecting analog and digital signals. Integrating the MTL 8937-HN into a control system is a fundamental step in ensuring compliance with global explosion protection standards (like ATEX, IECEx) for industries such as oil & gas, chemical, and pharmaceutical.

Product Parameters and Specifications

• Product Type: Modular Intrinsic Safety (IS) Barrier

• Manufacturer Part Number (MPN): 8937-HN

• Brand: MTL (MTL Instruments, part of the Cooper Industries division of Eaton)

• System Compatibility: Part of the MTL 8000 series modular system. Requires compatible MTL base units and power supplies for operation.

• Function: Provides intrinsically safe interfaces for 4-20 mA analog inputs (sinking) from field transmitters located in hazardous areas to a control system in the safe area.

• Channels: High-density, 4-channel module.

• Hazardous Area Ratings: Certified for specific gas and dust groups (e.g., [Ex ia] IIC for gases, indicative of the highest level of protection).

• Electrical Parameters (Typical):

  • Ui (Input Voltage): 250V AC max (safe area side).

  • Ii (Input Current): Specified limit.

  • Pi (Input Power): Specified limit.

  • Uo (Output Voltage): e.g., 28V DC max (hazardous area side).

  • Io (Output Current): e.g., 93 mA max (hazardous area side).

  • Co (Maximum External Capacitance): e.g., 83 nF.

  • Lo (Maximum External Inductance): e.g., 4.2 mH.

• Accuracy: High signal accuracy (e.g., ±0.1% of span) to ensure measurement fidelity.

• Mounting: Modules plug into a DIN-rail mounted MTL 8000 series base unit (carrier).

• Termination: Screw terminal connections.

Key Advantages and Features

The primary advantage of the MTL 8937-HN is its proven reliability and certified safety for protecting personnel and assets in explosive atmospheres. Its modular, high-density design (4 channels in a single module) saves significant space in marshalling cabinets compared to single-channel barriers. The module offers excellent signal integrity with low voltage drop and high accuracy, ensuring precise process measurement. It features a clear “healthy” LED indicator for each channel, providing instant visual confirmation of proper operation and power. The robust design ensures long-term stability and performance in industrial environments. As part of the MTL 8000 series, it offers great flexibility, allowing mix-and-match with other barrier types (for digital I/O, thermocouples, etc.) on the same DIN rail system. Using certified components like the MTL 8937-HN simplifies the system certification process for the entire installation.

Application Scenarios and Use Cases

This barrier is used wherever 4-20 mA measurement signals from Zone 0/1 or Zone 20/21 hazardous areas need to enter a safe-area control system like a DCS or PLC. Typical applications include:

• Oil & Gas Platforms/Refineries: Protecting signals from pressure, level, and temperature transmitters on tanks, pipelines, and reactors.

• Chemical Processing Plants: Interfacing analog signals from pH sensors, flow meters, and analytical instruments located in hazardous zones.

• Pharmaceutical Manufacturing: Providing safe interfaces for sensors in solvent handling or spray drying areas.

• Grain Silos and Food Processing: Protecting instruments in areas with combustible dust atmospheres.

In these applications, each channel of an MTL 8937-HN protects one 4-20 mA loop, allowing the critical process variable to be safely monitored and controlled.

Comparison with Competing Products

The MTL 8937-HN competes with other modular intrinsic safety barriers from manufacturers such as Pepperl+Fuchs (K-System), R. Stahl, Siemens (SITOP IS), and Phoenix Contact. Compared to traditional zener diode barriers, the MTL 8000 series offers active electronics, typically better accuracy, and diagnostic indicators. Versus competing modular systems, MTL is often recognized for its long heritage, wide global acceptance, and particularly robust and clear product documentation. The 4-channel density is a competitive feature, though some competitors offer similar density. The choice often comes down to corporate standards, existing installed base, regional supplier support, and specific certification requirements for the project.

Selection Guidelines and Important Notes

Selection Advice:

1. Hazardous Area Classification: The MTL 8937-HN must be selected for the correct gas/dust group (IIC, IIB, etc.) and temperature class (T6, T4, etc.) matching the hazardous area where the field device is installed.

2. Entity Parameter Matching: This is crucial. The safe-area equipment (the channel’s input on the DCS/PLC card) must have electrical parameters (Ui, Ii, Pi) that are greater than or equal to the barrier’s output parameters (Uo, Io, Po). The field device’s entity parameters (from its certificate) must be less than or equal to the barrier’s output parameters (Uo, Io) and the associated Co/Lo values.

3. System Configuration: The barrier requires a compatible MTL 8000 series base unit and a certified IS power supply. The entire loop, including wiring capacitance and inductance, must be within the Co and Lo limits.

4. Spare Capacity: It is common practice to install modules with spare channels (e.g., a 4-channel module even if only 3 loops are initially needed) for future expansion.

Important Precautions:

• Certified Installation: Installation must be performed in accordance with the manufacturer’s instructions and applicable explosion protection standards (IEC 60079-14). This often requires specially trained personnel.

• Segregation of Wiring: IS and non-IS wiring must be physically separated (in separate cable trays/conduits) as per standards to prevent energy leakage into the IS circuits.

• Correct Grounding: The IS ground (earth) connection for the barrier system is absolutely critical. It must be a dedicated, high-integrity ground with a very low resistance (typically <1 ohm), clearly labeled, and connected before applying power.

• Never Substitute: Do not replace an IS barrier with a standard signal conditioner or isolator. This would violate the safety certification and create an extreme hazard.

• Regular Inspection: IS systems should be included in regular plant inspection schedules to check for loose connections, damaged modules, or compromised grounding.

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