Description
Product Overview
The Woodward 9905-971 is a 16-channel discrete input module for the first-generation LINKnet distributed I/O system. It receives binary signals from field switches and relay contacts, then communicates their states to a compatible Woodward controller through the LON-based LINKnet network. The module is intended for remote status acquisition rather than direct control of field loads. Typical signal sources include equipment permissive contacts, auxiliary relay feedback, pressure-switch states, and machine status contacts, subject to the control application’s approved I/O allocation.
Each of the 16 inputs requires a 24 VDC sensing source. Woodward’s LINKnet module documentation describes an internal filtered and fused supply or an external 24 VDC source referenced to the module’s 24 V common. The documented input thresholds distinguish OFF below 8 VDC from ON above 16 VDC, leaving the intermediate range outside those stated logic thresholds. The specification also gives an input current of 13.1 mA per channel when ON at 24 VDC. For panel design and troubleshooting, these details matter: verify the field contact arrangement, common reference, source capacity, and wiring polarity rather than assuming the module behaves like a dry-contact input with no external sensing supply.
The 9905-971 is a legacy network node, not a generic 16-point PLC input card. In the 723PLUS LINKnet configuration documented by Woodward, it is assigned network address 7. That address is specific to the documented application and should not be copied blindly into another system; use the address defined by the installed control configuration. Woodward’s product change notice identifies the LON-based LINKnet modules as non-preferred and lists CANopen LINKnet HT products as the newer generation. Migration may require software and hardware changes, so a newer 16-channel input module should not be treated as a plug-in substitute without a system-level review.
Product Introduction
When a remote I/O node fails, the controller can lose visibility of multiple field contact states even if the main processor remains online. The Woodward 9905-971 provides 16 discrete input channels for collecting 24 VDC field signals over the legacy LINKnet network.
For replacement work, check the input thresholds, common-reference wiring, supply capacity, and network address. A matching channel count is not enough: this module belongs to the older LON-based LINKnet architecture, and newer CANopen nodes may require a planned migration.
Key Technical Specifications
| Parameter | Specification |
|---|---|
| Product model | 9905-971 |
| Manufacturer | Woodward |
| Product family | LINKnet |
| Product type | Discrete input module |
| Number of inputs | 16 |
| Nominal input voltage | 24 VDC |
| External input voltage range | 18–32 VDC |
| Module supply range | 18–32 VDC |
| OFF threshold | Below 8 VDC |
| ON threshold | Above 16 VDC |
| Input current | 13.1 mA per channel at 24 VDC when ON |
| Power consumption | 6.5 W at 24 VDC |
| Network architecture | LON-based LINKnet |
| Network wiring | Shielded twisted-pair |
| Isolation, network to I/O | 277 VAC |
| Isolation, power supply to network | 277 VAC |
| Isolation, power supply to I/O | 500 VDC |
| I/O channel-to-channel isolation | 0 V specified |
| Maximum field wire size | 14 AWG |
| Ambient temperature | −40 to +55°C |
| Documented 723PLUS network address | 7 |
Engineering note: The address 7 is documented for a specific 723PLUS LINKnet configuration, not a universal setting for every installation. The manual also specifies no isolation between individual I/O channels. Review the field common arrangement and grounding scheme before wiring mixed-source contacts.
9905-971
Related Products
These Woodward modules belong to the LINKnet distributed I/O family. Their signal functions differ, so they should not be treated as direct substitutes for the 9905-971.
- 9905-968 – Six-channel 4–20 mA analog input module for process transmitters.
- 9905-969 – Six-channel 4–20 mA analog input module with 24 VDC loop power.
- 9905-970 – Six-channel 100 Ω RTD input module for temperature measurement.
- 9905-972 – Six-channel 4–20 mA analog output module.
- 9905-973 – Eight-channel relay output module for discrete field commands.
- 9905-966 – J-type thermocouple input module with fail-high behavior.
- 9905-967 – J-type thermocouple input module with fail-low behavior.
- 8200-1204 – LINKnet HT 16-channel discrete input module in the newer CANopen-based product family.
The 8200-1204 is a potential migration reference, not a confirmed direct replacement. Woodward’s product change notice states that moving from LON LINKnet to CANopen LINKnet HT requires software changes in affected 5200 CPU systems. Confirm controller compatibility and migration requirements before specifying it.
Frequently Asked Questions
Q1: What is the Woodward 9905-971 used for?
The 9905-971 collects 16 discrete field signals from switches or relay contacts and reports their states to a compatible Woodward controller over LINKnet. It is intended for remote status acquisition, such as equipment permissives, auxiliary contact feedback, and process-switch monitoring. The actual signal assignments depend on the installed control application.
Q2: Can I hot-swap the 9905-971 while the control system is running?
Do not assume hot replacement is supported. The product documentation cited here does not establish a universal live-removal procedure. Review the applicable controller and LINKnet installation manuals, then assess the effect of losing all 16 input states before disconnecting the node. Follow the plant’s approved isolation and maintenance procedure.
Q3: Does the 9905-971 support firmware v3.1?
A general firmware v3.1 compatibility claim is not established by the module specifications. Compatibility depends on the host controller, LINKnet configuration, and application software revision. Confirm the exact software and hardware combination against the applicable Woodward documentation.
Q4: What voltage is required for the 9905-971 discrete inputs?
The inputs use a 24 VDC nominal sensing supply. The documented external input range is 18–32 VDC. The specified logic thresholds are below 8 VDC for OFF and above 16 VDC for ON. Signals in the interval between those thresholds should not be treated as guaranteed ON or OFF states. Check the field supply and voltage drop under actual operating conditions.
Q5: Can the 9905-971 be replaced by the newer 8200-1204?
Not as an assumed plug-in replacement. The 9905-971 uses the original LON-based LINKnet architecture, while the 8200-1204 belongs to the CANopen-based LINKnet HT family. A migration may involve controller hardware, network wiring, node configuration, and application software changes. Confirm the complete system architecture before approving the change.
Q6: Will replacing the 9905-971 erase the controller’s application logic?
The 9905-971 is a remote I/O module, not the primary controller application-storage device. Replacing it does not, by itself, mean that the main application logic will be erased. However, the node address, channel assignments, input logic, and controller references must be verified. Back up the configuration before maintenance and test all 16 input states after installation.
Q7: What should I check when purchasing a new-surplus or refurbished 9905-971?
Start with the full model marking and hardware revision on the actual unit. Inspect the enclosure, terminal blocks, communication connections, and circuit board for corrosion, damage, or signs of repair. Request a functional test covering all 16 channels, input threshold behavior, module power, and LINKnet communication. For refurbished stock, ask for the test conditions and results rather than relying on a general statement that the module was tested.
Engineering procurement note: The 9905-971 is a legacy LON LINKnet input node. Its 16-channel count is only one part of replacement compatibility. Confirm the 24 VDC sensing arrangement, input thresholds, common reference, network address, and host-controller support before installing a replacement.
