Allen-Bradley 1746-IG16 SLC 500 Digital DC TTL Input Module

The Allen-Bradley 1746-IG16, also cataloged as the 1746-IG16 Digital DC Input Module, serves as the primary TTL level input module utilized to execute 4.5–5.5 VDC signal acquisition across SLC 500 PLC platforms.

Configured for direct TTL and BCD signal interfacing in SLC 500 backplane scan cycles, the module converts 16-channel 5 VDC source-level inputs into discrete logic states for controller processing. Signal conditioning is optimized for low-voltage digital sources with tight switching thresholds and deterministic scan synchronization.

Suffix Breakdown & Model Matrix

No structured suffix or option code segmentation is defined for 1746-IG16. The model number represents a fixed SLC 500 catalog identifier without configurable hardware variants.

Hardware Specifications

Backplane Bus Communication and I/O Density Scaling

The module exchanges 16-point TTL input data through the SLC 500 backplane during cyclic scan execution. Backplane load is fixed at 140 mA @ 5 VDC, independent of input switching activity. I/O density scaling is fixed per module with no field expansion capability. Signal propagation follows deterministic scan timing governed by controller cycle execution.

TTL Input Threshold Behavior and Signal Conditioning

Input channels operate within 4.5–5.5 VDC logic levels. Internal threshold comparators stabilize signal transitions for TTL and BCD sources. Low signal delay (0.25–0.5 ms) supports high-speed digital state capture. OFF-state interpretation is defined by internal pull-down reference within module logic circuitry.

Frequently Asked Questions (FAQ)

Q: Does the 1746-IG16 support hot-swapping in an energized SLC 500 chassis?
A: No. Module insertion or removal must be performed with backplane power removed to prevent bus instability and logic corruption.

Q: What is the impact of full 16-channel activation on backplane load?
A: Backplane consumption remains fixed at 140 mA @ 5 VDC regardless of channel switching state.

Q: Can the module interface directly with 24 VDC field signals?
A: No. Input range is strictly limited to 4.5–5.5 VDC TTL levels; higher voltages require external signal conditioning.

Field Installation Guidelines

The module shall be installed in a single-slot SLC 500 chassis position with correct backplane alignment. The 1746-RT25B terminal block must be fully seated before energizing field circuits.

Wiring shall follow TTL signal integrity practices with short conductor runs and minimal loop area. Shielding should be grounded at a single panel reference point to reduce high-frequency coupling. Separation from AC and high-voltage DC wiring is required to prevent induced noise on low-level TTL inputs.