Product Overview

The Allen-Bradley 1756-IH16I​ (catalog variants include 1756-IH16I/A) is a 16-channel, 125 V DC digitally filtered sinking input module designed for installation in any I/O slot of a Rockwell Automation ControlLogix® programmable automation controller (PAC) chassis, such as the 1756-A7, A10, A13, or A17. As a member of the 1756 Série I/O family, the Allen-Bradley 1756-IH16I​ is engineered to sense the presence or absence of a 90–146 V DC field voltage at each of its sixteen inputs, making it ideally suited for interfacing with high-voltage DC discrete devices—such as limit switches, pushbuttons, relay contacts, and electronic proximity sensors—commonly found in utility substations, heavy-process plants, and legacy machinery where 24 V DC sensing is either impractical due to ground-loop concerns or where the field devices natively operate at higher nominal DC potentials.A defining characteristic of the Allen-Bradley 1756-IH16I​ is that each of its sixteen input channels is individually galvanically isolated from every other channel and from the ControlLogix backplane (250 V DC continuous isolation), providing superior immunity to common-mode noise, ground shifts, and potential differences between separate field circuits that would otherwise cause false triggering in non-isolated modules. The module supports Rockwell Automation’s advanced Sequence of Events (SOE) capability—each input can be configured to capture a time-stamped transition (rising or falling edge) with microsecond-level resolution (±200 µs typical relative to backplane time sync), enabling precise post-incident analysis of alarm cascades and interlock sequences. Input filtering is software-selectable per channel (0 ms, 1 ms, 2 ms, 9 ms, or 18 ms debounce) to reject contact bounce or electrical noise. The Allen-Bradley 1756-IH16I​ draws logic power from the ControlLogix backplane (5.1 V DC, approx. 125 mA) and requires a 36-position removable terminal block (1756-TBCH screw type or 1756-TBS6H spring-clamp type) for field wiring. Comprehensive LED diagnostics—per-channel input-active indicators plus Module OK and Force Active LEDs—facilitate rapid troubleshooting without a connected programming terminal.

Technical Specifications

Main Features and Advantages

The Allen-Bradley 1756-IH16I​ offers a combination of high-voltage DC compatibility, full channel-to-channel isolation, and advanced event-diagnostic features that set it apart from standard 24 V DC digital input modules in the ControlLogix lineup.Individually isolated inputs for noise immunity and floating-field wiring: Each of the sixteen inputs on the Allen-Bradley 1756-IH16I​ is optically and galvanically separated from its neighbors and from the backplane. This means field devices returning 125 V DC signals can originate from different power supplies, different grounds, or even floating circuits without creating ground loops or common-mode upset—a frequent requirement in retrofit projects tying into existing DC control circuits from disparate machinery or in substations where 125 V DC station battery systems are standard.Sequence of Events (SOE) with microsecond timestamping: When used with a ControlLogix controller that has time synchronization (via 1756-TIME module, EtherNet/IP CIP Sync, or GPS), the Allen-Bradley 1756-IH16I​ can log the exact time a contact closes or opens. This is invaluable for root-cause analysis after an unexpected shutdown—operators can see in the event log whether the emergency-stop tripped before or after a guard-door open, down to sub-millisecond resolution, rather than relying on scanned-state snapshots which may miss the order of fast-cascading events.