Honeywell 8937-HN Fiber Optic Extender Module – TDC 3000

Honeywell 8937-HN Fiber Optic Extender Module – LCN Segment Extension for TDC 3000 DCS

The Honeywell 8937-HN is a dedicated fiber optic extender module designed for the Local Control Network (LCN) backbone of the Honeywell TDC 3000 Distributed Control System. In large-scale continuous-process facilities — refineries, chemical complexes, power stations — the LCN must maintain deterministic, low-latency communication across physical distances that exceed the practical limits of coaxial copper media. The 8937-HN addresses this constraint by converting the LCN electrical signal to a multimode optical signal, transmitting it across fiber, and restoring the electrical signal at the remote node — all transparently, without protocol overhead or gateway latency.

Within the TDC 3000 control architecture, the LCN operates as the primary peer-to-peer data highway connecting High-Performance Managers (HPM), Application Modules (AM), History Modules (HM), and operator consoles. Any degradation in LCN signal integrity — whether from electromagnetic interference, ground-loop currents, or cable distance attenuation — directly impacts scan cycle determinism and alarm response time. The 8937-HN eliminates these failure vectors by substituting the copper segment with a galvanically isolated optical path, restoring full LCN bandwidth and timing compliance across inter-building or inter-unit distances.

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Technical Parameters

Hardware Logical Analysis

The 8937-HN operates at the physical layer of the LCN stack. Its core function is opto-electrical conversion: an onboard laser diode driver (or LED driver, depending on revision) modulates the LCN electrical signal onto the optical carrier, while a PIN photodiode receiver at the far end demodulates the optical signal back to the electrical domain. This conversion is entirely transparent to the LCN data-link layer — the token-passing arbitration logic in connected HPM or AM modules sees no difference between a copper segment and a fiber-extended segment.

EMC Design: Because the optical fiber carries no electrical potential, the 8937-HN inherently breaks all conducted EMI paths between LCN nodes. In environments with large motor drives, arc furnaces, or high-voltage switchgear, copper LCN coax is vulnerable to common-mode noise injection that can corrupt token frames and trigger spurious node resets. The fiber path eliminates this mechanism entirely. The module’s backplane interface includes transient suppression components to protect the card cage side from ESD events during installation or maintenance.

Ground Loop Elimination: Multi-building DCS installations frequently encounter ground potential differences of several volts between structures. On a copper LCN segment, this potential difference drives a circulating current through the cable shield, raising the noise floor and, in severe cases, damaging interface transceivers. The 8937-HN’s optical isolation sets the inter-segment impedance to effectively infinite, eliminating ground-loop current regardless of the potential difference between buildings.

Signal Regeneration: Unlike a passive fiber coupler, the 8937-HN performs active signal regeneration. The received optical signal is converted, re-timed, and re-transmitted as a clean electrical signal. This means the module does not accumulate jitter across cascaded segments — each fiber hop resets the signal timing budget, allowing longer total network spans without degradation of LCN frame integrity.

System Integration Benefits

• Deterministic LCN Scan Cycle Preservation: By eliminating noise-induced token losses, the 8937-HN maintains the LCN’s scheduled token rotation interval, ensuring HPM scan cycles execute at their configured period without jitter-induced overruns.
• Inter-Building Network Extension: Extends LCN segments across distances that exceed coaxial cable specifications — typically enabling spans of several hundred meters to over one kilometer depending on fiber grade and optical budget.
• Zero Protocol Overhead: The extension is transparent at the LCN data-link layer. No additional node addresses, gateway configurations, or routing tables are required. Existing TDC 3000 system software requires no modification.
• Hazardous Area Boundary Compliance: Fiber optic links carry no electrical energy into the field side, simplifying compliance with IEC 60079 zone classifications where intrinsic safety or increased safety requirements apply to cabling.
• Reduced Cable Infrastructure Cost: In new installations, fiber optic cabling is lighter, smaller in diameter, and easier to route through conduit than LCN coaxial cable, reducing material and labor costs for long inter-unit runs.
• Diagnostic Transparency: The 8937-HN does not mask LCN diagnostic traffic. Node health broadcasts, redundancy status messages, and alarm data traverse the fiber segment with the same priority and timing as on a copper segment, preserving full system diagnostic visibility at the operator console.
• Redundancy Architecture Support: In TDC 3000 installations with redundant LCN configurations, the 8937-HN can be deployed in pairs to provide redundant fiber paths, maintaining network availability during single-fiber or single-module failures.
• Long-Term Maintainability: The module slots into the standard TDC 3000 card cage without mechanical modification. Replacement requires no re-cabling of the copper LCN segments — only the fiber patch cables at each end need to be disconnected and reconnected, minimizing maintenance downtime.

Quality Assurance & Global Logistics

Every Honeywell 8937-HN unit dispatched from our Xiamen, China facility undergoes a structured pre-shipment verification process. Visual inspection covers the PCB surface, edge connector contacts, fiber port housings, and all passive components for signs of physical damage, oxidation, or prior repair. Where test fixtures are available, the module is powered within a TDC 3000-compatible card cage and the optical transmit power and receive sensitivity are verified against Honeywell’s published specifications. Serial numbers and hardware revision codes are recorded against each order for full supply-chain traceability.

Packaging follows ESD-safe protocols: the module is placed in a conductive foam-lined anti-static bag, sealed, and packed in a rigid corrugated carton with shock-absorbing foam inserts. For international shipments, moisture-barrier desiccant packs are included. Shipping documentation includes a commercial invoice, packing list, and — upon request — a Certificate of Conformance (CoC) and test report.

Logistics from Xiamen covers all major global destinations. Standard air freight to Europe, North America, Southeast Asia, and the Middle East typically achieves delivery within 3–7 business days. Express courier options (DHL, FedEx, UPS) are available for urgent requirements. All shipments are tracked end-to-end, with tracking numbers provided at the time of dispatch. Import documentation support, including HS code classification and commercial invoice preparation, is provided as standard.

Contact Information

Email: [email protected]
WhatsApp: +86 18359268345
Web: siemensplc.com
Location: Xiamen, China
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