Allen-Bradley 1746-IB8 SLC 500 Digital DC Input Module

Configured for DC signal acquisition in SLC 500 backplane scanning cycles, the Allen-Bradley 1746-IB8 (1746-IB8 Digital DC Input Module) provides direct electrical conversion of 24 VDC sinking field signals into 8-channel discrete input states within the SLC 500 controller I/O structure.

The module processes 10–30 VDC input signals with defined sink current behavior and transfers logic states through the backplane at fixed scan intervals. Input conditioning supports standard DC switching devices including pushbuttons and relay contacts with controlled response timing.

Suffix Breakdown & Model Matrix

No structured suffix segmentation is defined for 1746-IB8. The model designation represents a fixed catalog identifier within the SLC 500 digital input module family.

Hardware Specifications

SLC 500 Backplane Communication and Scan Behavior

The module exchanges discrete input states through the SLC 500 backplane bus during cyclic controller scan execution. Data mapping is fixed per 8-point structure with no configurable scaling or filtering layers. Backplane current draw remains constant at 50 mA @ 5 VDC independent of input switching activity.

DC Sinking Input Circuit Behavior

Input channels are configured as sinking inputs with internal current path referencing the module common. The 10–30 VDC input range ensures compatibility with standard industrial DC switching devices. OFF-state discrimination is defined at 1 mA leakage threshold to prevent false triggering under residual voltage conditions.

Frequently Asked Questions (FAQ)

Q: Does the 1746-IB8 support hot-swapping in an energized SLC 500 chassis?
A: No. Module insertion or removal must be performed with backplane power removed to avoid data corruption or electrical transient stress.

Q: What is the effect of all 8 channels switching simultaneously on backplane load?
A: Backplane current remains constant at 50 mA @ 5 VDC regardless of channel state transitions.

Q: Can firmware updates modify input behavior?
A: No firmware layer exists. Input processing is hardware-defined through fixed backplane scan logic.

Field Installation Guidelines

The module shall be installed in a compatible SLC 500 chassis with correct backplane alignment before energization. Terminal wiring must follow sinking input configuration rules with proper reference common routing.

Signal cables should be separated from high-voltage AC or high-frequency conductors to reduce induced coupling. Shield termination should follow single-point grounding practice at panel earth reference. Power isolation is required during module replacement to maintain backplane stability and prevent scan data corruption.