Application Scenarios
A refinery is adding a new sulphur recovery unit several hundred metres from the nearest control building. The project team wants to use the plant’s existing Honeywell Series 8 I/O and C300 controller rather than introduce a second control platform, but the I/O cabinets will sit in an electrically hostile location: adjacent to a large switchgear room, several hundred metres of cable run away, at a different earth potential from the controller cabinet.
Running copper I/O Link that distance is not viable — the cable would be exposed to induced transients, and the earth potential difference between the two buildings would introduce ground-loop noise into the I/O Link. Fitting 8937-HN modules at each end converts that span to multi-mode fibre. The copper I/O Link attaches to each extender over a short 0.5 m interface cable; the long run between buildings is fibre. The result is complete electrical separation between the two sites, immunity to the switchgear’s electromagnetic environment, and a redundant dual-link architecture that survives a single fibre cut.
The pain points this resolves repeat across distributed plant: the distance ceiling on copper I/O Link, ground loops between separately earthed buildings, EMI from drives and switchgear, and the cost of marshalling remote signals back to a central cabinet with separate wiring. For a plant extending an existing Series 8 installation, 8937-HN means new remote I/O drops onto the same controller, the same I/O modules and the same engineering tools — no second platform, no gateway, no protocol translation.
Parameter
| Main Parameters | Value/Description |
|---|---|
| Product Model | 8937-HN (replacement / successor: 8937-HN2) |
| Manufacturer | MTL Instruments (now Eaton) — supplied for Honeywell Series 8 I/O |
| Product Category | Fiber Optic Extender (FOE) — I/O Link media converter for Series 8 I/O |
| System Compatibility | Honeywell Series 8 I/O modules with S8 / C300 controller, Experion PKS |
| Function | Extends the I/O Link beyond the Series 8 cabinet, enabling remote I/O applications |
| Fiber Type | Multi-mode, 50/125 µm or 62.5/125 µm (confirm against module label) |
| Wavelength | 1310 nm (per distributor data — verify against the unit’s documentation) |
| Optical Power Budget | 8 dB — the figure that governs maximum achievable span (Honeywell Series 8 I/O User’s Guide) |
| Maximum Span | 1.5 km with standard fibre cable; 2 km with premium cable; 4 km maximum end-to-end for Series 8, less 0.25 km for each FOE in the path beyond the local site (Honeywell Series 8 I/O User’s Guide) |
| Fiber Connectors | ST-type; may be removed or replaced while active (Honeywell Series 8 I/O User’s Guide) |
| I/O Link Interfaces | Two redundant combo-cable interfaces — IOL1 and IOL2 — for high-availability redundant I/O Link |
| Interface Cables | Series 8-specific 0.5 m FOE interface cables: gray pair for IOL1, violet pair for IOL2; the correct cable type must be used or IOL communication becomes faulty or corrupted |
| Topologies Supported | Daisy chain, tree and star; repeater function uses the optical ports of two FOE modules |
| LED Indication | Green = power OK; yellow = communication signal present on Rx channel; yellow off = no communication signal (Honeywell Series 8 I/O User’s Guide) |
| Supply Voltage | 20–30 V DC |
| Current Consumption | 85 mA maximum at 20 V DC; 74 mA at 30 V DC |
| Operating Temperature | −20 °C to +70 °C (nominal distributor figure; 0–60 °C is also quoted — confirm on the module label) |
| Mounting | Series 8 chassis / cabinet plug-in with FOE back panel; DIN rail or panel mount depending on installation |
| Lifecycle Status | Obsolete / discontinued — Honeywell advises 8937-HN is superseded by 8937-HN2 |
