Allen-Bradley 1746-IO12 SLC 500 Digital I/O Combination Module

The Allen-Bradley 1746-IO12, also cataloged as the 1746-IO12 Digital I/O Combination Module, serves as the primary mixed-signal interface utilized to execute 120 VAC input acquisition and relay output switching across SLC 500 backplane I/O platforms.

Configured for combined discrete sensing and electromechanical output control, the module processes six 120 VAC input channels and drives six Form A relay outputs within a single-slot SLC 500 chassis configuration. Signal exchange is synchronized through backplane scan cycles with fixed timing characteristics.

Suffix Breakdown & Model Matrix

No structured suffix definition is provided for 1746-IO12. The model number represents a fixed catalog identifier within the SLC 500 combination I/O module family.

Hardware Specifications

Backplane Communication and Mixed I/O Scan Execution

The module exchanges both input state and output command data through the SLC 500 backplane during cyclic scan execution. Input channels are mapped as discrete points, while relay outputs are driven via backplane-controlled coil states. Backplane load remains within 70–90 mA @ 5 VDC regardless of switching activity.

Relay Output Switching Characteristics and Load Behavior

Output stage consists of six Form A relay contacts supporting AC and DC switching loads. Contact switching delay is governed by mechanical actuation with 35–45 ms response time. Current handling capability is defined per channel and limited by thermal dissipation across the module, with cumulative module current capped at 8.0 A.

Frequently Asked Questions (FAQ)

Q: Can the 1746-IO12 be hot-swapped in an energized SLC 500 chassis?
A: No. Backplane power must be removed before insertion or removal to avoid bus instability and unintended relay state transitions.

Q: Do output relays maintain state during backplane power loss?
A: No. Relay outputs de-energize on backplane power loss, returning to their default open state.

Q: Is input scanning independent of output relay switching?
A: Yes. Input acquisition and output control are handled as separate scan-mapped processes within the same backplane cycle.

Field Installation Guidelines

The module shall be installed in a single-slot SLC 500 chassis position with verified backplane alignment prior to energization. Terminal wiring shall follow separation rules between AC input circuits and relay output load wiring.

Relay output wiring must account for arc suppression depending on load type. Shielding and grounding practices shall use a single-point earth reference to reduce noise coupling on input circuits. Power isolation is required during module replacement to maintain backplane integrity and prevent unintended output activation.