Allen-Bradley 1756 ControlLogix Modules – 1756-OF6CI

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 facilities, offshore platforms, LNG terminals, and continuous process plants, the 1756 series represents Rockwell Automation's flagship control tier. Its modular backplane architecture supports hot-swap capability, redundant controller configurations, and deterministic real-time control — making it the reference standard for Safety Instrumented Systems (SIS) integration and DCS migration projects worldwide.

The 1756-OF6CI is a 6-channel isolated analog output module within this platform, providing 4–20 mA or 0–20 mA current output with per-channel isolation — a critical specification for installations where ground loops or high common-mode voltage differentials are present, such as in refinery field instrumentation loops.

The Evolution of 1756 ControlLogix Architecture

The 1756 ControlLogix platform was introduced in the mid-1990s as a successor to the PLC-5 and SLC 500 families. Its architecture is built around a high-speed ControlBus backplane, initially operating at 100 Mbps and later scaled to support Gigabit-class inter-chassis communication via the 1756-EN2T and 1756-EN3TR EtherNet/IP bridge modules.

Early revisions (Series A/B) of most 1756 modules used legacy firmware incompatible with Studio 5000 Logix Designer v30+. Series C and later revisions introduced Add-On Profile (AOP) support, enabling drag-and-drop configuration in modern engineering environments. The controller lineup evolved from the original 1756-L1 through the current 1756-L8x generation (GuardLogix 5580 / ControlLogix 5580), with a transition from 1MB to 40MB user memory and from serial-only programming ports to USB and dual-port EtherNet/IP.

Compatibility note: Chassis (1756-A4, 1756-A7, 1756-A10, 1756-A13, 1756-A17) are backward-compatible across all module generations. However, 1756-L8x controllers require firmware v30+ and are not backward-compatible with RSLogix 5000 v20 or earlier project files without conversion.

1756 ControlLogix Full Catalog & Functionalities (SKU List)

Controllers

• 1756-L71: ControlLogix 5570 controller, 2MB memory, standard control tier
• 1756-L73: ControlLogix 5570 controller, 8MB memory, mid-range process applications
• 1756-L83E: ControlLogix 5580 controller, 20MB memory, dual-port EtherNet/IP onboard
• 1756-L85E: ControlLogix 5580 controller, 40MB memory, high-density I/O tree support
• 1756-L7SP: ControlLogix redundancy module, paired with L7x controllers for hot-standby

Analog Output Modules

• 1756-OF6CI: 6-channel isolated current output, 4–20 mA, per-channel isolation, 16-bit resolution
• 1756-OF6VI: 6-channel isolated voltage output, ±10V / 0–10V, per-channel isolation
• 1756-OF8: 8-channel non-isolated analog output, current and voltage configurable

Analog Input Modules

• 1756-IF16: 16-channel single-ended analog input, 4–20 mA / voltage, 16-bit
• 1756-IF8: 8-channel differential analog input, high-resolution process measurement
• 1756-IF6I: 6-channel isolated analog input, per-channel isolation, field instrumentation use
• 1756-IR6I: 6-channel isolated RTD/resistance input, Pt100/Pt1000/Ni support
• 1756-IT6I: 6-channel isolated thermocouple input, J/K/T/E/R/S/B type support

Digital I/O Modules

• 1756-IB16: 16-channel 24VDC digital input, standard sinking input module
• 1756-OB16E: 16-channel 24VDC digital output, electronically fused, diagnostic feedback
• 1756-IA16: 16-channel 120VAC digital input, isolated group, field device monitoring

Communication & Network Modules

• 1756-EN2T: EtherNet/IP communication module, single-port, 100 Mbps, bridge/scanner
• 1756-EN3TR: EtherNet/IP module, dual-port, Device Level Ring (DLR) support
• 1756-CN2: ControlNet communication module, coax media, deterministic network
• 1756-DNB: DeviceNet scanner module, master node, up to 64 slave devices

Power Supplies

• 1756-PA72: 120/240VAC input power supply, 13A @ 1.2VDC backplane output
• 1756-PB72: 18–32VDC input power supply, 13A backplane, for DC-powered panels

Quality Control for the 1756 ControlLogix Range

The 1756 backplane operates on a proprietary high-speed serial bus. Modules that have suffered backplane connector damage, firmware corruption, or capacitor degradation may pass visual inspection but fail under load. DriveKNMS applies a structured test protocol for all 1756 modules:

• Backplane connector pin inspection and continuity verification
• Power-on self-test (POST) confirmation via chassis diagnostic LED sequence
• Channel-level functional test for all analog I/O modules using calibrated signal sources and measurement equipment (Fluke 725/726 or equivalent)
• Firmware version verification and compatibility check against target controller revision
• Burn-in cycle: minimum 24-hour powered operation under simulated load prior to shipment
• ESD-safe packaging with humidity indicator cards for international freight

Isolated analog modules such as the 1756-OF6CI and 1756-IF6I undergo additional inter-channel isolation resistance testing (>100MΩ at 500VDC) to confirm isolation integrity has not been compromised by field overvoltage events.