At a Glance. MTL barriers protect field instruments in hazardous areas by limiting energy. Choose by what the loop needs: shunt-diode zener barriers (MTL7706+, MTL7787+) are the classic low-cost choice for simple loops; galvanic isolators (MTL4544, MTL5544) add galvanic isolation, higher power and diagnostics; HART multiplexers (MTL831B, MTL838B) concentrate HART smart signals for asset management; fieldbus surge protectors (MTL SWK) shield Foundation Fieldbus segments; and line conditioners (MTL4850) power the HART bus. This guide gives the selection flow.
1. MTL Barrier Families Side-by-Side
| Family | Type | Key Benefit | Typical Loop | Stock Example |
|---|---|---|---|---|
| MTL7706+ | Zener shunt-diode | Lowest cost, compact | 2-wire transmitter, switch | MTL7706+ |
| MTL7787+ | Zener shunt-diode | Higher power, dual channel | 4–20 mA loops, solenoids | MTL7787+ |
| MTL4544 | Galvanic isolator | Isolation + power, no earth | Smart transmitters, higher voltage | MTL4544 |
| MTL5544 | Galvanic isolator | Isolation + HART transparency | HART smart instruments | MTL5544 |
| MTL831B / 838B | HART multiplexer | Multi-drop HART to asset mgmt | Dozens of HART instruments | MTL831B / MTL838B |
| MTL SWK | Fieldbus surge protector | Lightning / surge protection | Foundation Fieldbus segment | MTL SWK |
| MTL4850 | HART line conditioner | Power + impedance for HART bus | HART multidrop network | MTL4850 |
2. Decision Flow — Which MTL Barrier Do You Need?
- Is this a simple (non-smart) 2-wire loop? → Zener barrier MTL7706+ (economical, compact).
- Need higher power or dual channels? → MTL7787+.
- Using a smart/HART transmitter and need diagnostics? → Galvanic isolator MTL5544 (HART transparent) or MTL4544 (general isolation).
- Need galvanic isolation to break ground loops? → MTL4544 or MTL5544 (zener barriers reference ground).
- Many HART instruments need central asset management? → HART multiplexer MTL831B (slave) + MTL838B (master).
- Foundation Fieldbus segment exposed to lightning? → Surge protector MTL SWK.
- Building a HART multidrop network? → Line conditioner MTL4850.
3. Zener Barrier vs Galvanic Isolator — The Core Decision
| Aspect | Zener Barrier (MTL7706+) | Galvanic Isolator (MTL5544) |
|---|---|---|
| Isolation | No (references ground) | Yes (transformer / opto) |
| Power to field | From loop supply | Built-in, isolated |
| HART transparent | Yes (but check loading) | Yes, full transparency |
| Diagnostics | Limited | LED status, fault alarm |
| Grounding | Requires clean IS earth | No IS earth needed |
| Cost per channel | Lower | Higher (2–4×) |
4. Zone Classification and Approval Check
- Zone 0 / 1 / 2 (gas) or Zone 20 / 21 / 22 (dust) — confirm the barrier's ATEX / IECEx marking matches your field device and loop.
- Entity parameters: ensure Voc, Isc, Po of the barrier ≤ Vmax, Imax, Pi of the field instrument.
- IS earth: zener barriers need a dedicated, low-impedance intrinsic-safety earth (< 1 Ω); galvanic isolators do not.
- Zone 0: use a single channel barrier and check for "ia" (not "ib") rating for the most hazardous locations.
5. Quick FAQ
Q: Can I use a zener barrier with a HART transmitter?
Yes, most MTL zener barriers pass HART, but the loop must have enough voltage after the barrier drop. For long runs, prefer a galvanic isolator (MTL5544).
Q: Do galvanic isolators need IS earth?
No — this is their main advantage over zener barriers in sites without a clean IS earth.
Q: How many HART devices per MTL831B/838B?
The multiplexer system scales from 32 to thousands of points via racks.
Q: MTL SWK — one per segment?
Yes, install at the trunk entry to the hazardous area and at the power supply for full protection.
6. Related MTL Products in Stock
- MTL MTL7706+ — Zener shunt-diode barrier.
- MTL MTL7787+ — Dual-channel zener barrier.
- MTL MTL4544 — Galvanic isolator.
- MTL MTL5544 — HART transparent isolator.
- MTL MTL831B — HART multiplexer (slave).
- MTL MTL838B — HART multiplexer (master).
- MTL MTL SWK — Fieldbus surge protector.
- MTL MTL4850 — HART line conditioner.
Need help selecting the right MTL barrier for your hazardous-area loop? Request a quote with your zone classification, loop type and field device; our engineers will verify entity parameters and recommend the correct MTL model.