Allen-Bradley 1746-IH16/A​ SLC 500 16-Point 24V DC Sinking (NPN) Digital Input Module – High Density Discrete I/O

Product Overview

The Allen-Bradley 1746-IH16/A​ is a Bulletin 1746 SLC 500 Series 16-Point 24V DC Sinking (NPN-type) Digital Input Module manufactured by Rockwell Automation. Designed to interface dry-contact switches, NPN (sinking) proximity sensors, and other DC source-type field devices with an SLC 500 programmable controller, the Allen-Bradley 1746-IH16/A​ provides sixteen (16) discrete input points organized as two groups of eight, with optical isolation between the field side and the SLC 500 backplane. Each input point requires an external DC supply (typically 24V DC) connected to the common terminal; when a field device completes the circuit to the module’s input terminal, current sinks from the module into the sensor or switch, pulling the input logic high in the controller’s I/O image table.Installed in any slot of a 1746 SLC 500 chassis (such as the 1746-A4, 1746-A7, or 1746-A10) alongside an SLC 500 processor (SLC 5/03, 5/04, 5/05, or MicroLogix 1500 with appropriate adapter) and a 1746 series power supply, the Allen-Bradley 1746-IH16/A​ communicates input status to the processor via the chassis backplane at each I/O scan. Front-panel LED indicators provide one green LED per point to show real-time ON/OFF status, plus a module-status indicator for diagnostics. The “/A” revision reflects the current hardware revision incorporating improved component screening and ESD protection over early production runs of the 1746-IH16.The Allen-Bradley 1746-IH16/A​ operates over a nominal input voltage range of 10–30V DC (24V DC typical) and is designed for industrial environments with 500V AC optical isolation between field inputs and logic circuits, protecting the SLC 500 backplane from ground loops and transient surges. With a typical input delay of 8 ms off-to-on and 10 ms on-to-off (filter programmable via software on newer processors, fixed hardware filter on this module), it is well suited to typical machine and process discrete sensing where extremely fast response (< 1 ms) is not required but noise immunity and reliability are paramount. The module is powered from the chassis 5V DC backplane (drawing approximately 85 mA) and requires no external module power supply—only the 24V DC field voltage wired to the input commons. By consolidating sixteen sinking inputs in a single slot, the Allen-Bradley 1746-IH16/A​ delivers high-density, cost-effective discrete signal acquisition for legacy and ongoing SLC 500 installations worldwide.

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Description

 

Technical Specifications

Product Model | 1746-IH16/AManufacturer | Rockwell Automation / Allen-BradleyProduct Type | SLC 500 16-Point 24V DC Sinking (NPN) Digital Input ModuleNumber of Inputs | 16 (sinking type, current sinks into module)Input Voltage Range | 10–30V DC (nominal 24V DC)Input Current (per point @ 24V DC) | 8.0 mA typical (max 9.5 mA)ON State Voltage (min/max) | 10V DC min to turn ON; 30V DC max continuousOFF State Voltage (max) | 5V DC max to guarantee OFFInput Impedance | Approx. 2.8 kΩ @ 24V DCResponse Time (Hardware Filter) | OFF→ON: 8 ms typ.; ON→OFF: 10 ms typ.Backplane Current Draw (5V DC) | 85 mA typicalIsolation (Field to Backplane) | 500V AC rms for 1 minute (optical)Indicating LEDs | 16 point LEDs (green, ON = input active) + Module Status LEDTerminal Arrangement | Uses 1746-N2 or 1746-NT4B removable terminal blocks (not included)Compatible Chassis | 1746-A4, 1746-A7, 1746-A10, 1746-A13 SLC 500 chassisCompatible Processors | SLC 5/01, 5/02, 5/03, 5/04, 5/05; also works in MicroLogix 1500 with 1769-UM2 adapter (special config)Operating Temperature | 0 °C to +60 °C (32 °F to 140 °F)Storage Temperature | -40 °C to +85 °CRelative Humidity | 5% to 95% non-condensingDimensions (H × W × D) | 141 × 33 × 127 mm (5.55 × 1.3 × 5.0 in.)Certifications | UL listed, cULus, CE marked, C-TickWire Size (with terminal block) | 14–22 AWG solid or stranded copper

Main Features and Advantages

High-density sinking input in a single slot: The Allen-Bradley 1746-IH16/A​ packs sixteen 24V DC sinking inputs into one SLC 500 chassis slot, reducing the number of modules required in a typical panel and leaving more slots free for analog I/O, special-function modules, or output cards. This high point-count-per-slot ratio directly lowers installed system cost and panel footprint—particularly valuable when retrofitting older relay-logic panels into a compact SLC 500 enclosure.Optical isolation for field-noise immunity: Each group of eight inputs on the Allen-Bradley 1746-IH16/A​ shares a common terminal (two commons total—inputs 0–7 on Common 0, inputs 8–15 on Common 1) and is optically isolated from the SLC 500 backplane at 500V AC. This isolation blocks ground-loop currents and attenuates inductive-transient coupling from contactors, solenoids, or VFDs that may share the same 24V DC supply, a frequent cause of false triggering or backplane damage in unprotected designs. The Allen-Bradley 1746-IH16/A​ therefore preserves both signal integrity and processor health in electrically noisy machine environments.Direct compatibility with NPN (sinking) sensors and dry contacts: Many industrial proximity switches, photoelectric sensors, and limit switches are wired as NPN (sinking) devices—the sensor switches the negative side of the load to ground while the positive side is tied to a 24V DC supply. The Allen-Bradley 1746-IH16/A​ is specifically designed for this wiring convention: the field device connects between +24V DC and the input terminal, and the module’s internal sinking circuit provides the return path to 0V (DC common) when the input is active. Dry-contact devices (pushbuttons, selector switches, relay NO contacts) can also be connected directly, with the external 24V DC supply providing the wetting voltage—no interposing relays or extra interface cards are needed.Per-point LED diagnostics for rapid troubleshooting: Sixteen individually labeled green LEDs on the faceplate of the Allen-Bradley 1746-IH16/A​ mirror the logical state of each input point in real time. During commissioning or fault investigation, a technician can instantly see whether a particular limit switch or sensor is registering at the module without connecting a laptop, measuring voltage with a multimeter, or opening the program—a significant time-saver on large machines with dozens of inputs spread across multiple racks.Broad SLC 500 ecosystem compatibility and long lifecycle support: The Allen-Bradley 1746-IH16/A​ works with all SLC 500 processors and chassis generations that support 1746-series I/O, and is fully recognized by RSLogix 500 / Studio 5000 (via import) with no special configuration files required—just drop it into the I/O configuration at the correct slot number. It uses the standard 1746-N2 screw-terminal block (or 1746-NT4B for high-density applications) which is interchangeable across most 1746 digital I/O modules, simplifying spare-parts inventory. Rockwell Automation continues to support the SLC 500 platform with available spares and replacement modules, making the Allen-Bradley 1746-IH16/A​ a dependable choice for maintaining and incrementally expanding legacy automation systems.Robust industrial construction: The Allen-Bradley 1746-IH16/A​ is built on a rigid PCB with gold-plated backplane edge connectors and conformal coating options on later batches, rated for 0–60 °C ambient and 5–95 % non-condensing humidity. Its removable terminal block allows the module to be swapped without disconnecting field wiring—a critical feature during unplanned downtime when every minute counts. The module latches securely into the 1746 chassis tongue-and-groove rail and is keyed to prevent insertion into an incorrectly addressed slot via software I/O check during power-up.

Contact Us WhatsApp / Wechat：+86 18150087953
Phone：+86 18150087953
Email：sales@cxplcmro.com

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