Woodward 9905-971 | 24-Channel Discrete Input Module

Woodward 9905-971 24-Channel Discrete Input Module with Latent Fault Detection

High-Speed Discrete Inputs for Turbine Control

The Woodward 9905-971 functions as a discrete input module within the 9900 series. It provides 24 channels for monitoring digital field signals. Update time is only 5 ms, with timestamp resolution at 1 ms. Therefore, this module captures fast-changing events with excellent precision. Each discrete input operates at 24 Vdc.

For relay outputs, the 9905-971 includes latent fault detection. This feature is critical in fault-tolerant systems. A single fault might otherwise go undetected. However, when a second fault occurs, it could cause an unexpected shutdown. Latent fault detection prevents this scenario.

Mechanical Installation and Removal

The module inserts into card guides inside the control chassis. It then connects directly to the motherboard. Two screws, one at the top and one at the bottom of the front panel, secure the module in place. Additionally, two handles are provided at the top and bottom. When you push these handles outward, the module moves out just far enough. This action disengages the boards from the motherboard connectors. Consequently, removal becomes quick and tool-free.

Contact Wetting Voltage Options

Each of the four modules accepts six contact inputs. The control itself or an external source can supply the contact wetting voltage. Each relay module requires a contact wetting voltage of 24 Vdc. For sourcing this voltage, you have three options:

• Internal 24 Vdc power source from the control

• External 18-32 Vdc power source

• External 100-150 Vdc power source

All discrete inputs are fully isolated. Nevertheless, you must establish a common reference point between the inputs and the contact power source. Jumpers are required between relay module terminals 33, 34, and 35 when using the internal 24 Vdc source. If an external source is used, connect the external source's common to terminals 34 and 35.

How Latent Fault Detection Works on the 9905-971

The Woodward 9905-971 detects relay failures without affecting the relay output state. One relay output consists of six individual relays. When the output closes, all six relay contacts close. Due to the series-parallel configuration, even the failure of any two individual relays will not cause the output to open. Individual relays open and close in pairs regularly. This ensures they are in the correct state and can change state properly.

Similarly, when a relay output is open, all six contacts remain open. The failure of any one relay will not cause the output to close. Individual relays close and reopen one at a time for testing. Readback circuitry detects the state of each relay contact. Any errors are reported immediately. Further testing halts without affecting the relay output contact or control operation. Note that latent fault detection is not suitable for all applications or circuits.

Packaging List

• Woodward 9905-971 discrete input module (1 pc)

• Mounting screws (top and bottom, 2 pcs)

• Handles (pre-installed on module)

• Quick reference card

• No certificate or warranty document included

Note: No certificate or warranty document is included in the package.

Shipping Information

We ship all orders via FedEx, UPS, or DHL. Delivery takes 3–7 business days worldwide. Tracking number will be provided within 24 hours after dispatch.

Frequently Asked Questions (FAQ)

1. How many discrete input channels does the Woodward 9905-971 provide?
The 9905-971 provides 24 discrete input channels. Each channel accepts 24 Vdc signals. Update time is 5 ms with 1 ms timestamp resolution.

2. What is latent fault detection on this module?
Latent fault detection tests individual relays inside each output. It verifies they can change state correctly. This detection happens without affecting the actual output state or control operation.

3. Can I use an external power source for contact wetting?
Yes, you can use an external 18-32 Vdc source or an external 100-150 Vdc source. Connect the external source's common to terminals 34 and 35 of the relay module.

4. How do I remove the 9905-971 from the chassis?
Push the two handles outward (top and bottom). This moves the module forward slightly. The boards then disengage from the motherboard connectors. After that, pull the module out by hand.

5. Is the Woodward 9905-971 suitable for safety-critical applications?
Latent fault detection makes it suitable for many fault-tolerant systems. However, the documentation notes that latent fault detection is not appropriate for all applications or circuits. Review your specific safety requirements before use.