9905-971 Woodward Discrete Input Module

Description:

Functional Description
9905-971, a Discrete Input Module by Woodward, features latent fault detection for each relay output. It operates on a voltage of 24 Vdc for its discrete inputs and allows the use of normally open or closed contacts for each relay output. These modules are fitted into card guides within the control chassis and linked to the motherboard. They are secured in place with two screws at the front panel's top and bottom, complemented by handles that facilitate easy removal from the motherboard connectors when toggled outward.

Features
The control comprises four modules, each accommodating six contact inputs. Contact wetting voltage can be supplied either by the control itself or an external source, with each relay module requiring a 24 Vdc contact wetting voltage. This voltage can be sourced from an external 18-32 Vdc or 100-150 Vdc power supply.
To ensure full isolation of discrete inputs, a common reference point between the inputs and the contact power source is necessary. If using the internal 24 Vdc power source for contact wetting, jumpers must connect terminals 33, 34, and 35 of the relay module. For external power sources, the common terminal must be connected to the discrete input commons (terminals 34 and 35) of the relay module.

Latent Fault Detection
In fault-tolerant systems, detecting latent faults is crucial as undetected faults can lead to system shutdowns upon encountering additional faults. Relay failures can be detected without altering the relay output state through latent fault detection configured in discrete outputs.
Each relay output consists of six individual relays arranged in a series-parallel configuration. When closed, all six contacts are engaged, and the failure of any two relays won't cause the output to open. To ensure proper functioning and state changes, relays are operated in pairs. Conversely, when open, all six contacts are disengaged, and the failure of any single relay won't close the output. Relays are individually cycled open and closed to verify their correct operation. Any detected discrepancies in the readback circuitry trigger error reports, halting further testing without impacting the relay output contact or control operations. However, latent fault detection may not be suitable for all applications or circuit configurations.

Datasheet Link:

9905-971 Woodward Discrete Input Module PDF Datasheet