At a Glance. The MTL 4500 and 5500 series are MTL’s two workhorse galvanic isolator families for analog signals in process plants, and the single-channel 4-20 mA models are the ones most often cross-shopped. The MTL4544 and the MTL5544 are nearly twin specifications on paper: one channel in, one channel out, 4-20 mA with HART transparency, ±0.1% accuracy, a 20-35 VDC supply range and ATEX / IECEx / FM approvals on both. The deciding difference is the isolation topology: the MTL4544 provides 3-way isolation (input / output / power) and is SIL 2 capable, while the MTL5544 provides 2-way isolation (input / output) without a SIL rating. If your loop feeds a safety instrumented function or your power rail must be galvanically separated from the signal path, the 4544 is the required choice; for standard BPCS analog inputs where 2-way isolation is enough, the 5544 does the same signal job at a friendlier cost.
1. Head-to-Head: MTL4544 vs MTL5544
| Specification | MTL4544 | MTL5544 |
|---|---|---|
| Channels | 1 | 1 |
| Input / Output | 4-20 mA + HART | 4-20 mA + HART |
| Isolation | 3-way (input / output / power) | 2-way (input / output) |
| Accuracy | ±0.1% | ±0.1% |
| SIL rating | SIL 2 capable | — |
| Power supply | 20-35 VDC | 20-35 VDC |
| Approvals | ATEX, IECEx, FM | ATEX, IECEx, FM |
| Best for | SIL loops, full 3-port separation, hazardous-area analog inputs | Standard analog isolation where power and signal share a common reference |
| Product page | MTL4544 | MTL5544 |
Because both units pass HART transparently, your handheld communicator or asset-management system works through either isolator without re-addressing — the selection is driven by the isolation and safety requirements of the loop, not by the signal type.
2. Where the MTL4544 Pulls Ahead
Safety instrumented loops. The 4544’s SIL 2 capability makes it the default pick wherever the isolator sits inside a trip loop and the safety case must quote certified hardware fault tolerances. Its 3-way isolation also means a fault or surge on the 24 VDC power rail cannot propagate into the field or logic-side signal conductors — the property that defines a true 3-port isolator.
Mixed power architectures. In marshalling cabinets where field circuits, system power and redundant supplies come from different sources, 3-way isolation removes the ground-loop and reference-shift problems that 2-way devices can leave behind.
3. Where the MTL5544 Pulls Ahead
Cost-optimized BPCS loops. For the hundreds of ordinary monitoring loops in a plant — transmitters feeding a DCS that are not part of any SIF — 2-way isolation between input and output is usually all the galvanic separation the circuit needs. The 5544 delivers the identical ±0.1% signal accuracy and HART transparency in that role.
Spare-parts rationalization. If your installed base is already 5500-series-heavy, standardizing on the MTL5544 keeps config, spares and DIN-rail layout consistent. The wider 5500 family covers the same hazardous-area signal ranges as the 4500 family, so one series can populate the whole cabinet.
4. Isolators vs Shunt-Diode Barriers
Both isolators are often compared against MTL’s shunt-diode range — the MTL7706+ and MTL7787+. The distinction is simple: shunt barriers are the most economical intrinsic-safety interface but require a genuinely isolated, safety-earthed power supply and impose a resistance budget on the loop; isolators such as the 4544/5544 provide active galvanic isolation, tolerate non-isolated supplies and simplify loop calculations. For new panels, most engineers default to isolators; for dense digital I/O on a proven IS design, barriers remain cost-effective.
5. Replacement and Cross-Reference
A frequent procurement question is whether the MTL5544 can replace an existing MTL4544 (or vice versa) during a failure or long-lead-time situation. The rule:
- 4544 → 5544: acceptable only if the loop is demonstrably not part of a safety function and the cabinet’s power/signal reference scheme tolerates 2-way isolation. Re-validate the loop drawing before substituting.
- 5544 → 4544: always electrically acceptable (3-way is a superset of 2-way) and the standard upgrade path when a loop is later absorbed into an SIF.
- Check supply headroom in both cases: both need 20-35 VDC at the terminals.
Send Glorient your existing isolator model and loop tag and we will confirm the nearest in-stock crossover within one business day. For HART multidrop and multiplexer applications, see the MTL831B and MTL838B HART multiplexers and the MTL4850 HART line conditioner.
6. Decision Summary
| Your situation | Recommended model |
|---|---|
| Loop inside an SIF / requires SIL rating | MTL4544 (SIL 2 capable) |
| Power rail must be isolated from signal path | MTL4544 (3-way isolation) |
| Standard monitoring loop, cost-driven | MTL5544 |
| Dense digital IS I/O, budget interface | MTL7706+ / MTL7787+ shunt barriers |
7. FAQ
Can the MTL5544 replace the MTL4544 in an existing SIL 2 loop?
No. The 5544 carries no SIL rating, so any loop whose safety case references the isolator must keep a SIL-capable unit such as the MTL4544. For non-safety loops the substitution is usually fine after a drawing check.
Do both isolators pass HART without configuration?
Yes. Both are specified for 4-20 mA with HART, so communicators and asset-management tools work transparently through either unit.
What is the practical difference between 2-way and 3-way isolation?
2-way (the 5544) isolates input from output. 3-way (the 4544) additionally isolates the power supply from both signal sides, which prevents power-rail disturbances from reaching field or logic conductors and is the basis for its SIL 2 capability.
Where can I browse more MTL isolation products?
See the full MTL brand page for barriers, isolators, HART multiplexers and surge protectors in stock.