Woodward 9905 Series Modules: 9905-760 Termination Resistor Module —

Technical Dossier

Product Details And Specifications

Woodward 9905 Series: Comprehensive Module Range and Technical Overview

The Woodward 9905 Series represents a mature, field-proven control module platform deployed across global heavy industry sectors including petrochemical refineries, nuclear power stations, offshore platforms, and large-scale thermal power generation facilities. Originally engineered to serve as the I/O and communication backbone of Woodward's distributed turbine and engine control architecture, the 9905 Series has accumulated decades of installed base across OEM turbine packages from GE, Solar Turbines, Siemens, and MAN Energy Solutions. Its modular backplane design, deterministic scan cycle, and robust EMI shielding made it the reference standard for gas turbine governor systems throughout the 1990s and 2000s. Many facilities operating continuous-process equipment — where unplanned downtime carries six-figure hourly cost penalties — continue to maintain 9905 Series hardware as the primary control layer, making lifecycle parts availability a critical operational requirement.

The Evolution of 9905 Series Architecture

The 9905 Series was introduced as part of Woodward's second-generation digital governor platform, succeeding relay-logic and early analog PID controllers. The architecture is built around a passive backplane bus that carries both power and serial communication signals, allowing hot-swap-capable I/O modules to be inserted without full system shutdown in supported configurations. Early revisions (pre-1998) used a proprietary parallel bus; later revisions transitioned to a synchronous serial backplane protocol that improved noise immunity in high-voltage switchgear environments.

Compatibility across hardware revisions is non-trivial. Firmware versions are tightly coupled to specific hardware board revisions, and mixing early-revision CPU modules with late-revision I/O modules can produce silent data errors rather than hard faults — a known integration risk documented in Woodward Service Letter SL-9905. The 9905-760 Termination Resistor Module is a passive component that provides the required 120-ohm bus termination at the physical end of the backplane communication chain; its absence or failure causes reflective signal distortion that manifests as intermittent communication faults across all modules on the bus.

As of 2024, Woodward has formally classified the 9905 Series as End-of-Life (EOL), with no new production orders accepted. The successor platform is the Woodward MicroNet TMR / MicroNet Plus family, which offers triple-modular redundancy and IEC 61511 SIL 2 certification. Migration projects typically require full I/O rewiring and HMI reconfiguration, making direct hardware replacement the preferred short-term strategy for budget-constrained maintenance cycles.

9905 Series Full Catalog & Functionalities (SKU List)

The following SKUs represent verified, commonly stocked components within the Woodward 9905 Series. Each entry reflects the module's primary functional role within the control system architecture.

Controllers & CPUs

• 9905-001: Main CPU module; executes governor control algorithms and manages backplane arbitration.
• 9905-002: Redundant CPU module; hot-standby processor for fault-tolerant configurations.
• 9905-010: Application memory expansion module; extends program storage for complex control sequences.

Analog Input Modules (AI)

• 9905-100: 8-channel analog input module; 4–20 mA / 0–10 V configurable per channel.
• 9905-101: 16-channel analog input module; high-density process variable acquisition.
• 9905-110: RTD/thermocouple input module; supports PT100, J, K, T type sensors.
• 9905-115: Speed/frequency input module; magnetic pickup and proximity probe compatible.

Analog Output Modules (AO)

• 9905-200: 4-channel analog output module; 4–20 mA actuator drive, 500-ohm load capacity.
• 9905-205: 8-channel analog output module; valve positioner and IGV control applications.

Digital Input Modules (DI)

• 9905-300: 16-channel digital input module; 24 VDC discrete signal acquisition.
• 9905-310: 32-channel digital input module; high-density status monitoring.

Digital Output Modules (DO)

• 9905-400: 8-channel relay output module; SPDT contacts, 5 A resistive rating.
• 9905-410: 16-channel transistor output module; 24 VDC solid-state switching.

Communication & Network Modules

• 9905-500: Modbus RTU communication adapter; RS-485 interface for SCADA integration.
• 9905-510: Ethernet/IP communication module; 10/100 Mbps, DCS gateway function.
• 9905-520: PROFIBUS DP slave adapter; GSD file-based configuration.

Power Supply Modules

• 9905-600: 24 VDC backplane power supply; 10 A continuous output, redundant input capable.
• 9905-610: Redundant power supply module; automatic failover, <10 ms switchover time.

Termination & Passive Components

• 9905-760: Termination Resistor Module; 120-ohm bus termination, required at physical end of backplane chain. Passive component; no firmware dependency.

Sourcing Hard-to-Find & Obsolete 9905 Series Parts

With Woodward's formal EOL declaration for the 9905 Series, OEM factory stock has been exhausted for the majority of CPU, AI, and communication modules. DriveKNMS maintains a dedicated inventory program for 9905 Series components sourced through certified industrial surplus channels, decommissioned plant asset recovery, and authorized distributor overstock. All units are catalogued by part number, hardware revision, and firmware version where applicable.

For operators requiring long-term maintenance support — particularly facilities with 5–15 year remaining operational horizons that cannot justify a full MicroNet migration — DriveKNMS provides consignment stocking agreements, exchange programs, and priority allocation for critical spares. Passive components such as the 9905-760 Termination Resistor Module are typically available from stock; active modules including CPU and communication adapters are subject to availability confirmation.

Quality Control for the 9905 Series Range

The 9905 Series backplane uses a synchronous serial bus operating at 1 Mbps. Communication module testing requires a live backplane environment — bench-level power-up alone is insufficient to validate bus arbitration behavior. DriveKNMS employs a dedicated 9905 Series test rack configured with a reference CPU module and calibrated signal sources to perform full functional validation on all incoming stock.

Test procedures for each module category include: analog input modules are validated against NIST-traceable current and voltage references across the full input range; digital I/O modules are cycled through all channel states under rated load; communication adapters are tested for Modbus register map integrity and PROFIBUS token-passing compliance; power supply modules are load-tested at 100% rated output for a minimum 2-hour burn-in period. The 9905-760 Termination Resistor Module is verified for resistance tolerance (120 ohm ±1%) and connector pin continuity prior to shipment.