Woodward 9905 Series Modules 9905-760 Termination Resistor Module

Technical Dossier

Product Details And Specifications

Woodward 9905 Series Technical Notes

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.