In a hazardous area, the signal between a field instrument and the safe-area control system must be made intrinsically safe — incapable of releasing enough energy to ignite a flammable atmosphere. The two dominant methods are the zener barrier (shunt-diode) and the galvanic isolator. This guide compares the MTL7706+ barrier and the MTL5544 isolator so you can pick the right protection.
At a Glance: The Short Answer
Choose a zener barrier (MTL7706+) when cost matters most and a reliable earth connection is available — the classic choice for simple 4–20 mA loops. Choose a galvanic isolator (MTL5544) when you need HART transparency, no earth-loop issues, higher accuracy or three-way isolation.
Side-by-Side Comparison
| Feature | Zener Barrier (MTL7706+) | Galvanic Isolator (MTL5544) |
|---|---|---|
| Principle | Shunt diodes + resistor to earth | Transformer / opto isolation |
| Earth required | Yes (critical) | No |
| HART transparency | Limited | Yes |
| Accuracy / drift | Good | Better (3-way isolation) |
| Channels | 1 (7706+) / 2 (7787+) | 1 (5544) |
| Zone | Zone 0 | Zone 0/1 |
| Cost | Lower | Higher |
When to Choose the Zener Barrier (MTL7706+)
The MTL7706+ Shunt-Diode Barrier is the world's most widely installed IS barrier — a single-channel unit for 4–20 mA loops in Zone 0, with ATEX, IECEx and FM approvals. Choose it when:
- You have a reliable, low-impedance earth (the barrier shunts fault energy to ground).
- You run simple analogue loops without HART diagnostics.
- Budget and panel space favour the lowest-cost solution.
For digital signals, the MTL7787+ is the 2-channel equivalent, saving DIN-rail space in high-density marshalling cabinets.
When to Choose the Galvanic Isolator (MTL5544)
The MTL5544 Galvanic Isolator provides three-way isolation (field / system / power) with HART transparency. Choose it when:
- You need HART communication for smart-instrument diagnostics.
- You want to avoid earth-loop problems — galvanic isolation removes the earth dependency.
- Your application demands higher accuracy and stability.
For SIL-rated loops, the MTL4544 adds SIL 2 capability with the same isolation benefits.
Scaling to Large Plant Networks
For plants with many HART devices, MTL also provides:
- MTL831B — 32-channel HART multiplexer (single Modbus/Ethernet link).
- MTL838B — 64-channel high-density HART multiplexer.
- MTL4850 — HART line conditioner for noisy 4–20 mA loops.
- MTL SWK — fieldbus surge protection for FOUNDATION Fieldbus / PROFIBUS-PA.
Decision Guide
- Simple 4–20 mA loop, reliable earth, budget-sensitive? → Zener barrier (MTL7706+).
- Need HART diagnostics? → Galvanic isolator (MTL5544).
- Earth-loop problems or high accuracy? → Galvanic isolator (MTL5544).
- SIL-rated loop? → MTL4544 (SIL 2).
- Many HART devices? → MTL831B / MTL838B multiplexer.
Get a Quote
Glorient supplies the full MTL intrinsic-safety range — MTL7706+ barriers, MTL5544 isolators, HART multiplexers and surge protection. Send us your loop schedule and we will recommend the correct protection. Request a quotation and we will respond within 24 hours.