Product Overview

The Allen-Bradley 1746-IV16​ is a sixteen-channel digital DC input module belonging to the SLC 500 modular programmable controller family. It plugs into any available I/O slot of a 1746 chassis and provides the interface between 24V DC field devices and the SLC processor, converting the ON/OFF state of switches, sensors and auxiliary contacts into logic levels that the CPU reads from its input image table. Because all sixteen channels are packed into a single slot, the 1746-IV16​ offers one of the highest input densities available on the platform, making it the standard choice where rack space is limited and point counts are high.Electrically, the 1746-IV16​ is a sourcing input module, meaning the module itself supplies the positive signal voltage to the input loop and the connected field device completes the circuit to the DC common. This behaviour suits NPN-type current-sinking sensors, dry contacts, pushbuttons, limit switches and relay contacts that do not generate their own signal voltage. Each channel accepts a nominal 24V DC with a broad 10–30V DC operating window, and internal filter circuitry combined with optical coupling rejects the electrical noise that is typical of industrial panels carrying motor starters, contactors and variable frequency drives.In a control system, the value of the 1746-IV16​ lies in its combination of density, ruggedness and serviceability. Sixteen LED indicators on the front face show the live state of every channel, so commissioning and fault finding can be done without a programming terminal. A removable terminal block allows the entire field wiring to be prepared on the bench and transferred to the module, and it permits a failed module to be replaced without disturbing a single conductor. Supported across SLC 5/01 through 5/05 processors in both local and remote I/O configurations, the Allen-Bradley 1746-IV16​ remains a workhorse for maintaining and extending installed SLC 500 systems.

Technical Specifications

Main Features and Advantages

High channel density in one slot: The Allen-Bradley 1746-IV16​ delivers sixteen discrete DC inputs in a single-slot module, which is the highest input density in the SLC 500 digital range. In a seven-slot chassis this allows nearly a hundred input points to be accommodated without adding expansion racks, and it directly reduces the cost per point of the I/O system. For plants expanding an existing rack where free slots are scarce, the 1746-IV16​ frequently eliminates the need for a second chassis, power supply and remote I/O adapter.Sourcing configuration for simple field wiring: The 1746-IV16​ is a sourcing module, so it provides the positive side of the input loop and the field device only has to switch the return path to the DC common. This makes it particularly convenient for dry contacts, mechanical limit switches, pushbuttons, relay auxiliary contacts and NPN current-sinking proximity sensors, which represent the majority of devices found on machinery. Wiring is straightforward: the supply positive is landed on the module’s DC terminal, and each device is wired between its input terminal and the common.Noise-immune signal acquisition: The Allen-Bradley 1746-IV16​ incorporates filter circuitry and optical coupling on every channel, and it specifies a maximum off-state voltage of 5V DC and a maximum off-state current of 1 mA. These thresholds mean that leakage currents, induced voltages from parallel cable runs and contact bounce will not falsely register as a logic one, which is a common failure mode in panels where input cables share a tray with motor power conductors.Fast, deterministic response: With a typical 0.3 ms ON and 0.5 ms OFF transition on resistive loads, the 1746-IV16​ responds quickly enough for high-speed applications such as part detection on sorting lines, registration marks on packaging machines and encoder-adjacent counting duties. Where extra debounce is needed for mechanically noisy contacts, the input filter characteristic brings the maximum transition time to 8 ms, still well within the scan expectations of most SLC 500 applications.Designed for fast service: Every channel of the 1746-IV16​ is mirrored by its own LED on the front of the module, so an electrician can confirm whether a sensor has actually switched simply by looking at the rack. The removable terminal block is the second service feature that matters: field conductors stay terminated in the block, and a replacement module can be fitted by releasing two retaining screws and swinging the block onto the new unit. Downtime is measured in minutes, and the risk of mis-wiring during a midnight repair is essentially removed.Low power burden on the chassis supply: The Allen-Bradley 1746-IV16​ draws only 85 mA from the 5V backplane and nothing from the 24V backplane rail. Even with several modules installed, the chassis power budget is rarely the limiting factor, and the modest 3.6 W dissipation keeps cabinet temperatures manageable in densely packed enclosures.Hazardous location approval: The 1746-IV16​ carries North American Class I Division 2 approval for Groups A, B, C and D, along with UL, c-UL and CE marking. This allows the same module to be used in general-purpose machines and in classified process areas, which simplifies spare parts stocking for operators with mixed installations.