Allen-Bradley 1771 PLC-5 Modules: 1771-OFE3 Analog Output,

Technical Dossier

Product Details And Specifications

Allen-Bradley 1771 PLC-5 Series Technical Notes

The Allen-Bradley 1771 I/O system is the foundational hardware platform of the Rockwell Automation PLC-5 programmable controller family. Deployed across heavy industrial sectors — including petrochemical refineries, nuclear power generation facilities, offshore oil platforms, pulp and paper mills, and continuous-process chemical plants — the 1771 backplane architecture represents one of the most widely installed legacy DCS/PLC infrastructures in global industrial history. Installed base estimates place active 1771-series hardware in tens of thousands of facilities across North America, Europe, and Asia-Pacific, many of which operate on 20–40 year maintenance cycles with no near-term migration path. The 1771-OFE3 is a 4-channel analog output module within this platform, providing 4–20 mA or 0–10 VDC isolated outputs for process control loops.

The Evolution of 1771 Architecture

The 1771 I/O platform was introduced by Allen-Bradley in the late 1970s as a modular, rack-based I/O subsystem for the PLC-2 and later PLC-5 controller families. The architecture uses a parallel backplane bus operating at TTL logic levels, with each I/O chassis accommodating up to 16 single-slot or 8 double-slot modules. Early revisions (Series A, B) established the physical form factor and backplane pinout that remained backward-compatible through subsequent decades. Series C and D modules introduced enhanced diagnostics, improved noise immunity, and extended temperature ratings for harsh environments. The 1771 platform reached end-of-life announcement from Rockwell Automation in the early 2000s, with active production of most modules ceasing by 2012–2015. However, the installed base remains substantial, and Rockwell continues to offer limited repair services. Third-party MRO suppliers such as DriveKNMS provide new-surplus, refurbished, and tested-exchange units to extend operational life. Migration paths include the ControlLogix 1756 platform with 1771-to-1756 adapter bridges (1771-AENTR), though full migration requires significant engineering effort and is deferred by most end-users.

1771 Full Catalog & Functionalities (SKU List)

The following SKUs represent verified, commonly stocked modules within the Allen-Bradley 1771 PLC-5 I/O platform. Modules are classified by functional category.

Analog Output Modules

• 1771-OFE3: 4-ch isolated analog output, 4–20 mA / 0–10 VDC, 12-bit resolution
• 1771-OFE1: 2-ch analog output, 4–20 mA, non-isolated, single-slot
• 1771-OFE2: 4-ch analog output, 0–10 VDC / 4–20 mA, non-isolated
• 1771-OF: 2-ch analog output, 4–20 mA, early-series baseline module

Analog Input Modules

• 1771-IFE: 8-ch analog input, 4–20 mA / 0–10 VDC, 12-bit, single-ended
• 1771-IFE-A: 8-ch analog input, 4–20 mA, Series A revision with enhanced filtering
• 1771-IFE-B: 8-ch analog input, 0–5 VDC / 1–5 VDC, Series B
• 1771-IF: 4-ch analog input, 4–20 mA, early-series baseline module
• 1771-IXHR: 4-ch thermocouple/mV input, high-resolution, isolated

Digital Output Modules

• 1771-OBD: 32-pt DC output, 24 VDC, 0.5 A per point, double-density
• 1771-OB: 16-pt DC output, 24 VDC, 1 A per point, standard density
• 1771-OW16: 16-pt relay output, Form C contacts, 2 A per point
• 1771-OA: 16-pt AC output, 120 VAC, 1 A per point, triac-based

Digital Input Modules

• 1771-IBD: 32-pt DC input, 24 VDC, double-density, sink/source selectable
• 1771-IB: 16-pt DC input, 24 VDC, standard density
• 1771-IA: 16-pt AC input, 120 VAC, standard density

Specialty / Communication Modules

• 1771-SDN: DeviceNet scanner module for 1771 chassis, Class 1 explicit messaging
• 1771-ASB: Remote I/O adapter, links 1771 chassis to PLC-5 via RIO cable
• 1771-AENTR: EtherNet/IP adapter, bridges 1771 I/O to ControlLogix 1756 systems

Quality Control for the 1771 Range

The 1771 backplane uses a parallel TTL bus with module-specific I/O image table mapping. Quality verification for 1771 modules requires chassis-level functional testing rather than standalone bench testing. DriveKNMS employs the following test protocol for 1771 modules: (1) Visual inspection for capacitor ESR degradation, relay contact wear, and conformal coating integrity. (2) Backplane continuity verification across all 60-pin connector positions. (3) Functional load test in a live 1771 chassis with a PLC-5 processor executing a dedicated diagnostic ladder program. (4) For analog modules (including 1771-OFE3): calibration verification against NIST-traceable reference instruments, with output accuracy confirmed at 0%, 25%, 50%, 75%, and 100% of full scale. (5) 48-hour burn-in cycle at elevated ambient temperature (45°C) to screen early-life failures. All tested units are issued a DriveKNMS inspection report with test date, technician ID, and measured parameters.