Allen-Bradley 1746-IA8 SLC 500 Digital I/O Module

Configured for AC signal acquisition in SLC 500 backplane scan cycles, the Allen-Bradley 1746-IA8 (1746-IA8 AC Input Module) provides direct electrical conversion of 100/120 V AC field states into 8-point discrete input data within the SLC 500 controller architecture.

The module samples 85–132 V AC input signals at 47–63 Hz and resolves each channel into backplane-updated logic states synchronized to controller scan execution. Input circuitry is designed for defined leakage discrimination and inrush handling for mechanical contact devices.

Suffix Breakdown & Model Matrix

No formal suffix segmentation is defined for 1746-IA8. The model identifier represents a fixed catalog structure within the SLC 500 I/O family without configurable ordering code extensions.

Hardware Specifications

Backplane Bus Communication and I/O Scan Behavior

The 1746-IA8 exchanges input state information through the SLC 500 chassis backplane during deterministic scan cycles. Data is mapped as fixed 8-point digital words with no field-level scaling. Backplane current draw is limited to 5 VDC logic rail consumption, remaining constant regardless of channel switching activity.

AC Input Conditioning and Transient Handling

Input stages implement impedance conditioning to stabilize 85–132 V AC field signals. Inrush current tolerance up to 0.8 A supports relay and mechanical switch closure events. OFF-state detection uses leakage current discrimination up to 2 mA to prevent false triggering under induced or residual voltage conditions.

Frequently Asked Questions (FAQ)

Q: Can the 1746-IA8 be hot-swapped in an energized SLC 500 rack?
A: No. The module is not intended for live insertion. Backplane power should be isolated prior to installation or removal to prevent bus corruption.

Q: Does channel switching affect backplane power consumption?
A: No. Backplane draw remains fixed at 0.050 A @ 5 VDC independent of input state transitions.

Q: Is firmware upgrade or configuration supported?
A: No firmware layer exists. Input behavior is fully hardware-defined through backplane scan mapping.

Field Installation Guidelines

Installation shall be performed in a compatible SLC 500 chassis slot with verified backplane alignment. The removable terminal block shall be fully seated before energizing field circuits.

AC input wiring must be separated from low-voltage control conductors to minimize induced coupling. Shield termination should follow single-point grounding practice at the panel earth reference. Power isolation is required during module replacement to maintain backplane integrity and avoid transient data corruption.