Allen-Bradley 1756-OF4 ControlLogix Analog Output Module: Specs, Compatible SKUs & Availability

Technical Dossier

Product Details And Specifications

Allen-Bradley 1756 ControlLogix Series Technical Notes

The Allen-Bradley 1756 ControlLogix platform is one of the most widely deployed programmable automation controller (PAC) architectures in global heavy industry. Installed across petrochemical refineries, nuclear power generation facilities, offshore oil & gas platforms, pulp and paper mills, and large-scale water treatment plants, the 1756 chassis-based system has served as the backbone of process and discrete control since its commercial introduction in the late 1990s. The 1756-OF4 is a 4-channel analog output module within this platform, designed for precision voltage and current signal generation to field devices including control valves, variable frequency drives, and positioners.

The Evolution of 1756 ControlLogix Architecture

The ControlLogix platform was introduced by Rockwell Automation in 1997 as a successor to the PLC-5 and SLC 500 families. The architecture is defined by a modular, chassis-based backplane (1756-Ax series) that supports hot-swappable I/O, redundant controller configurations, and distributed I/O via ControlNet, DeviceNet, EtherNet/IP, and SERCOS interfaces.

Generation 1 (1997–2004): Initial release of the 1756 chassis with Series A I/O modules. Limited channel density; firmware updates delivered via PCMCIA cards on early L1/L2 controllers.

Generation 2 (2004–2012): Introduction of Series B and C I/O modules with improved noise immunity and expanded diagnostics. Controllers scaled from the 1756-L55 to the 1756-L63/L64. EtherNet/IP became the dominant communication backbone.

Generation 3 (2012–2020): Launch of the ControlLogix 5570 (L7x) and 5580 (L8x) controller families. Increased memory, faster scan times, and CIP Security support. Many Series A/B I/O modules declared end-of-life but remain in active service globally.

1756 ControlLogix Full Catalog & Functionalities (SKU List)

Analog Output Modules

• 1756-OF4: 4-channel analog output; ±10V / 0–20mA / 4–20mA; 16-bit resolution; isolated outputs.
• 1756-OF8: 8-channel analog output; voltage and current output; 16-bit resolution; single-ended.
• 1756-OF8H: 8-channel HART-enabled analog output; supports HART pass-through for smart field device communication.
• 1756-OF6VI: 6-channel isolated voltage output; ±10V range; high-isolation for noise-sensitive environments.
• 1756-OF6CI: 6-channel isolated current output; 0–20mA / 4–20mA; designed for long cable runs.

Analog Input Modules

• 1756-IF8: 8-channel analog input; voltage/current configurable per channel; 16-bit resolution.
• 1756-IF16: 16-channel analog input; high-density; single-ended; 16-bit resolution.
• 1756-IF6I: 6-channel isolated analog input; current input; 24-bit resolution; for precision measurement.
• 1756-IF6CIS: 6-channel isolated current input with HART support; simultaneous sampling.
• 1756-IR6I: 6-channel isolated RTD/resistance input; supports Pt100, Pt1000, Ni120, and custom curves.
• 1756-IT6I: 6-channel isolated thermocouple input; supports J, K, T, E, R, S, B, N types.

Digital Output Modules

• 1756-OB16D: 16-channel 24VDC digital output; diagnostic per-point; electronically fused.
• 1756-OB32: 32-channel 24VDC digital output; high-density; sourcing type.
• 1756-OA16: 16-channel 120/240VAC digital output; triac-based; zero-crossing switching.

Digital Input Modules

• 1756-IB16: 16-channel 24VDC digital input; sinking; standard response time.
• 1756-IB32: 32-channel 24VDC digital input; high-density; sinking type.
• 1756-IA16: 16-channel 120VAC digital input; standard response; screw terminal.

Controller Modules

• 1756-L71: ControlLogix 5570 controller; 2MB user memory; single Ethernet port.
• 1756-L83E: ControlLogix 5580 controller; 40MB user memory; dual Ethernet ports; CIP Security.

Communication & Infrastructure Modules

• 1756-EN2T: EtherNet/IP communication module; 100Mbps; supports DLR and linear topologies.
• 1756-CN2: ControlNet communication module; coax-based; deterministic I/O scanning.
• 1756-PA72: 120/240VAC power supply; 10A backplane current; standard chassis power.
• 1756-PB72: 18–32VDC power supply; 10A backplane current; for DC-powered panels.

Sourcing Hard-to-Find & Obsolete 1756 ControlLogix Parts

A significant portion of installed 1756 ControlLogix systems worldwide operate on Series A and Series B I/O modules that Rockwell Automation has discontinued from standard production. Facilities operating these systems face a binary choice: full platform migration (capital-intensive, requiring re-engineering and re-validation) or lifecycle extension through qualified spare parts sourcing.

Quality Control for the 1756 ControlLogix Range

The 1756 platform's backplane communication protocol (ControlBus) and the module-level electronic keying system require that all replacement modules pass both hardware-level and firmware-level verification before installation in a live system.

DriveKNMS applies the following test protocol to all 1756 series modules: