Description
Product Introduction
The Woodward 9905-973 is an 8-channel discrete relay output module built for distributed actuation within Woodward LINKnet control architectures. Deployed heavily across gas turbines, steam turbines, and large industrial engine control systems, this module handles pilot solenoid actuation, trip circuit triggers, remote alarm annunciation, and motor starter commands. It converts digital control commands sent over the LINKnet serial network into physical dry-contact closures.
Unlike low-power solid-state output cards, the 9905-973 houses high-capacity electromechanical relays capable of switching real-world field loads up to 10 A. Mounting this module locally at the engine skid or valve junction box eliminates high-current AC/DC wire runs back to the main control room. Its opto-isolated control interface prevents inductive field surges and inductive contact arcing from breaching the core MicroNet or Atlas processor backplane.
Key Technical Specifications
| Parameter | Specification |
| Manufacturer | Woodward |
| Part Number | 9905-973 |
| Module Type | LINKnet 8-Channel Relay Module |
| Output Channels | 8 Independent Relay Outputs (Form A / SPST) |
| Contact Rating | 10 A @ 250 VAC / 10 A @ 30 VDC |
| Logic Input Voltage | 18 to 32 VDC (24 VDC Nominal) |
| Power Consumption | 14 W Typical |
| Network Isolation | 1000 Vrms (0–60 Hz) / 277 VAC channel-to-network |
| Operating Temperature | -40°C to +55°C (Extended bounds up to +85°C node dependent) |
| Diagnostics | Functional Fault LED & Channel Relay Status LEDs |
| Mounting Format | Modular LINKnet Node Base Panel / DIN Mount |
Application Scenarios & The “Trench” Experience
Picture this: It’s 3:30 AM during a peak power demand cycle. An auxiliary lube oil pump starter contact fails on a dual-fuel gas turbine node. The relay contact welded shut on the old 9905-973 output card due to an unsuppressed inductive surge from the contactor coil. The main governor throws a relay output fault and inhibits the start sequence. Down time costs $50,000 an hour, and operations can’t bypass the interlock. Swapping in a pre-tested, high-isolation 9905-973 replacement gets the pump interlock cycling and brings the turbine back online in 15 minutes.
- Gas Turbine Fuel Skid Actuation: Driving fuel shut-off solenoid valves and igniter power contactors.
- Emergency Shutdown (ESD) Systems: Tripping master fuel trip (MFT) relays and alarm horns across generator skids.
- Marine Engine Auxiliaries: Controlling seawater cooling pump starters and remote thruster hydraulic valves.
- Balance of Plant (BOP) Control: Interfacing lower-level 24 VDC LINKnet commands to high-voltage 120/230 VAC breaker trip coils.
9905-973
9905-973
Transparency SOP: Quality Assurance & Testing
We don’t just ship surplus boxes—we test them on live Woodward node bases. Every 9905-973 undergoes a strict bench test sequence:
- Inbound Physical Inspection: Visual check for heat-stressed relay enclosures, PCB trace damage, terminal block wear, and OEM serial label integrity.
- Logic Power-On Test: Module is mounted on a LINKnet test rack. We apply 24 VDC power and verify the boot-up sequence and logic current draw.
- 8-Channel Active Switching Load Test: We sequence all 8 relays using LINKnet comms commands. Every contact set is tested under a resistive load to verify contact resistance stays under 50 mΩ when closed.
- Relay Coil & Isolation Check: High-potential test between the switching contacts and the logic bus to confirm the optocouplers and relay coils haven’t suffered breakdown.
- Anti-Static Packaging: Cleared modules are cleaned, sealed in ESD shielding bags, and securely packed in customized foam boxes prior to dispatch.
The Veteran’s Tech Trap Guide
- ⚠️ Snub Your Inductive Loads: Electromechanical relays will pit and weld if you drive raw DC solenoid coils or heavy AC contactors without flyback protection. Always install a flyback diode across DC coils or an RC snubber across AC coils directly at the load.
- ❗ Match Node DIP Switch Addresses: When replacing a failed card, match the node address rotary or DIP switches on the new unit or base to the old card’s exact position. If the address doesn’t match, the CPU will throw a missing output node fault instantly.
- ⚠️ Verify Contact Current Limits: While rated for 10 A, running all 8 channels continuously at max current will cause localized thermal buildup inside closed skids. Derate continuous loads to 6–7 A per point if ambient enclosure temperatures exceed 50°C.
- ❗ Do Not Pull Under Load: Never disconnect the terminal block or pull the module while field circuits are actively energizing high-current loads. Arcing on the terminal pins will ruin the connector housing.
Frequently Asked Questions
Q: Is the Woodward 9905-973 hot-swappable?
A: No. You must kill power to both the module logic supply and the field contact power before removing the module from its node base. Pulling it live risks backplane communication glitches on adjacent LINKnet nodes.
Q: What is the main difference between the 9905-971 and the 9905-973?
A: The 9905-971 is a 16-channel Discrete Input module used to read field switch states into the system. The 9905-973 is an 8-channel Relay Output module used by the system to drive high-power external equipment.
Q: Can I drive 120 VAC and 24 VDC loads on the same 9905-973 module?
A: Yes, provided the wiring meets local electrical codes for voltage separation on adjacent terminals. Because each channel uses isolated relay contacts, you can switch different voltage sources across separate channels.
Q: What warranty comes with these modules?
A: Every new surplus or field-tested refurbished Woodward 9905-973 module comes with a full 12-month replacement warranty.
Q: Why choose surplus or refurbished over an OEM system upgrade?
A: Woodward has retired the original LINKnet product line. Finding new surplus or certified refurbished units allows you to restore critical plant operations immediately without spending six figures to rewrite your controller code and upgrade the entire control cabinet.
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