ABB SLMG99 — Compact, DIN-rail–mounted Signal Limiter for Intrinsically Safe Loop Integrity

Let’s be honest—signal limiters aren’t glamorous, but when you’re protecting a level transmitter in a Zone 1 chemical dosing skid or safeguarding thermocouple inputs in a refinery control room, the SLMG99 quietly earns its keep. From my experience supporting field engineers across EPC projects in the Gulf and Northern Europe, this unit shows up where reliability trumps flashiness: small cabinets, tight budgets, and environments where a single spark could cascade into downtime—or worse.

Key Features

• Two-channel isolated limiting — Each channel independently limits voltage/current (e.g., caps 4–20 mA loops at 20.5 mA ±0.1 mA), preventing overdrive to downstream I/O cards. One thing I appreciate is how cleanly it handles mixed-signal scenarios—say, a 4–20 mA pressure signal feeding a PLC while also driving a local analog meter.
• Intrinsically safe (IS) certified output — Certified per IEC/EN 60079-27 (Entity concept), with a Group II C approval. It seems to be one of the few sub-20 mm wide limiters that maintains full IS compliance without requiring external Zener barriers.
• No external power required — Powered loop-powered (via input side), so no separate 24 V DC feed needed. In many cases, this simplifies cabinet layout—especially in retrofit jobs where adding power rails means rewiring half the panel.
• DIN-rail mounting with spring-clamp terminals — Fits standard TS35/7.5 or TS35/15 rails. You might notice that terminal torque is forgiving (0.5 N·m max), which helps avoid stripped screws during high-volume commissioning.
• Visual status indication — Dual-color LED per channel (green = normal, red = limit active or fault). Field techs consistently tell us this cuts diagnostic time by ~40% compared to units relying solely on multimeter checks.

Technical Specifications

Application Fields

The SLMG99 typically lands in applications where analog signal integrity is non-negotiable—and space or power is scarce. Think: offshore platform fire & gas panels (limiting HART-enabled gas detector outputs before they hit safety PLCs), pharmaceutical cleanroom HVAC controllers (preventing overshoot on humidity sensor feedback), or modular skids for water treatment where every millimeter counts. It’s not built for high-speed data acquisition—but if your priority is “don’t fry the $1,200 analog input card,” it’s often the pragmatic pick over more complex isolators.

Advantages & Value

• Procurement simplicity — No need to coordinate barrier resistors, separate power supplies, or recalibrate entire loops. Reduces BOM count and engineering review cycles.
• Compatibility-first design — Works seamlessly with legacy ABB 800xA, Siemens Desigo, Honeywell Experion, and most third-party analog I/O modules. We’ve seen zero reported compatibility issues in >1,200 deployed units across 2022–2024.
• Cost efficiency — Typically priced 30–40% below comparable dual-channel IS isolators with similar certifications—without sacrificing certification rigor.
• Support responsiveness — ABB’s regional technical support responds to configuration queries within 4 business hours (based on 2023 internal SLA tracking). Firmware isn’t applicable here—but wiring diagrams, calibration sheets, and explosion-proof mounting kits ship with every order.

Installation & Maintenance

Mount it in a standard IP54 or higher control cabinet with ≥100 mm clearance above/below for airflow—no forced ventilation needed. Avoid direct exposure to condensation or conductive dust (e.g., carbon black in tire plants). Wiring should follow IEC 60079-14: keep intrinsically safe and non-IS cables separated by ≥50 mm or use grounded metal dividers. No routine calibration is required—the limit threshold is factory-set and drift is <0.05% per year (per ABB’s 2023 QA report). Just wipe the housing with a dry lint-free cloth every 6 months; firmware updates don’t apply (it’s analog-only).

Quality & Certifications

Certified to:

• IEC/EN 60079-27:2014 (Intrinsic Safety – Entity concept, Group II C, T4)
• IEC/EN 61326-1:2013 (EMC for industrial environments)
• RoHS 2011/65/EU compliant (lead-free PCB, halogen-free casing)
• CE marked, UL Recognized (E482223) for Class I, Div 2 / Zone 2

Backed by a standard 365-day warranty. If failure occurs under normal operating conditions, replacement ships within 1 week for in-stock units—or within 30 days maximum for custom configurations. All units are traceable to batch and production date via laser-etched serial code on the housing.