MTL MTL4851 HART Multiplexer – Scalable HART access for 4–20 mA loops in process plants

The MTL4851 is a HART multiplexer module designed to give maintenance and asset teams non-intrusive access to HART data across existing 4–20 mA loops. From my experience, it’s the straightforward way to bring advanced diagnostics into your AMS/PRM without touching the DCS I/O strategy. You might notice that it typically pairs with MTL4500/5500 series HART‑pass-through isolators, so you can poll dozens of field devices from a single RS‑485 line—clean, simple, and robust for brownfield upgrades.

Company’s Order Placement Process and Guarantees

• Warranty period: 365 days
• Delivery time: typically 1 week for in-stock items; no more than one month at the latest
• Payment method: 50% advance payment; full payment prior to delivery
• Express delivery methods: FedEx, UPS, DHL

Key Features

• Non-intrusive HART access – Polls HART FSK signals superimposed on 4–20 mA loops without disrupting control, which is ideal for live plants.
• Multi-channel architecture – Scales from typical 16 up to 32 channels per node (depending on the backplane/carrier), so you can start small and expand later.
• RS‑485 (Modbus‑RTU) host interface – Connects to asset management systems like AMS/PRM/FieldCare via standard RS‑485, typically up to 115.2 kbps.
• Compatible with MTL4500/5500 isolators – Works with HART pass‑through modules such as MTL5541/MTL5544 to keep intrinsic safety and diagnostics neatly separated.
• Safe‑area mounted – The multiplexer sits in the safe area; the field side remains protected by your IS isolators or barriers.
• Simple retrofit – In many cases, you can reuse existing marshalling and add HART access without rewiring transmitters or stopping the process.
• Status indication – Front status indicators for power and communications make first-line troubleshooting quick.

Technical Specifications

Related or Supporting Products

• MTL4850 – Companion HART multiplexer module; used in similar architectures where different channel densities or system roles are required.
• MTL5541 / MTL5544 – 2‑/4‑wire transmitter isolators with HART pass‑through, typically paired with MTL4851 for intrinsic safety on the field side.
• MTL4500 series isolators – High‑density IS isolators with HART pass‑through for compact cabinets; good fit when modernizing legacy marshalling.
• RS‑485 accessories – Termination resistors, shielded twisted pairs, and USB‑to‑RS‑485 converters for host connectivity.

Many customers tell us the MTL4851 plus MTL5541 isolators is a sweet spot: they keep their DCS I/O untouched, pull device diagnostics into AMS, and cut routine walkdowns by more than half.

Installation & Maintenance

• Cabinet & environment – Install in a clean, dry, ventilated cabinet meeting IEC/UL industrial control panel practices. Allow space for heat dissipation; avoid mounting near high-heat sources.
• Wiring & grounding – Use shielded twisted pair for RS‑485; terminate the bus at both ends and respect biasing. Maintain a single-point ground strategy and keep IS and non‑IS wiring segregated.
• Backplane/carrier – Mount the MTL4851 on the designated backplane or DIN carrier. Channel allocation should align with your HART pass‑through isolators to avoid cross‑talk.
• Addressing & baud rate – Set unique Modbus node IDs; choose conservative baud rates for long runs. From my experience, 38.4 kbps is a stable default in most cabinets.
• Safety – Power down before inserting/removing modules. The multiplexer is safe‑area equipment; field loop protection and IS compliance must be handled by the isolators/barriers.
• Routine maintenance – Quarterly visual checks for loose terminations and dust. Verify RS‑485 termination, inspect shields, and keep firmware/config tools up to date. No calibration is normally required.

Quality & Certifications

• CE compliant; designed for industrial EMC environments
• UL/cUL for industrial control equipment (typical for MTL modules)
• RoHS compliant; manufacturer operates ISO 9001 quality systems
• Manufacturer’s warranty: typically 1 year; our supply warranty: 365 days as stated above