Allen-Bradley ControlLogix 1756 Modules – 1756-IR12 Analog Input Module

Technical Dossier

Product Details And Specifications

Allen-Bradley ControlLogix 1756 Series Technical Notes

The Allen-Bradley ControlLogix 1756 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 infrastructure, the 1756 chassis-based system provides deterministic control, high-availability redundancy, and a modular I/O architecture that has made it the reference standard for process-critical applications since its commercial introduction in the late 1990s. The 1756-IR12 is a 12-channel RTD/Resistance analog input module within this platform, designed for precision temperature and resistance measurement in demanding industrial environments.

The Evolution of ControlLogix 1756 Architecture

The ControlLogix 1756 architecture was introduced by Rockwell Automation in 1997 as a successor to the PLC-5 and SLC 500 platforms. The original chassis design supported up to 17 slots and used the ControlBus backplane for inter-module communication. Early firmware revisions operated under RSLogix 5000 v1.x and supported basic discrete and analog I/O with limited diagnostics.

From 2003 onward, the introduction of SERCOS, DeviceNet, and EtherNet/IP communication adapters expanded the 1756 platform into distributed I/O topologies. The 1756-EN2T and 1756-EN2TR modules established dual-port EtherNet/IP as the dominant network layer for ControlLogix installations. Concurrent with this, the analog I/O module range was expanded to include high-density variants (e.g., 1756-IF16, 1756-OF8) and specialized signal types including RTD, thermocouple, and HART-enabled modules.

By 2010, the introduction of the L7x controller series (1756-L71 through 1756-L85E) brought 64-bit processing, expanded memory, and integrated EtherNet/IP ports. The current generation L8x series (1756-L81E through 1756-L85E) supports CIP Security, TLS-encrypted communications, and SD card-based firmware management. Legacy modules from the original 1756 release remain physically compatible with current chassis hardware, though firmware and Logix Designer version constraints apply to mixed-generation configurations.

ControlLogix 1756 Full Catalog & Functionalities (SKU List)

Analog Input Modules

• 1756-IR12: 12-channel RTD/Resistance analog input, ±0.1% accuracy, supports Pt, Cu, Ni sensor types
• 1756-IF8: 8-channel single-ended voltage/current analog input, 16-bit resolution
• 1756-IF16: 16-channel single-ended analog input, high-density voltage/current
• 1756-IF6I: 6-channel isolated analog input, voltage and current, 16-bit
• 1756-IT6I: 6-channel isolated thermocouple/millivolt analog input
• 1756-IT6I2: 6-channel isolated thermocouple input, enhanced cold junction compensation

Analog Output Modules

• 1756-OF8: 8-channel single-ended analog output, voltage/current, 16-bit
• 1756-OF6VI: 6-channel isolated voltage analog output
• 1756-OF6CI: 6-channel isolated current analog output

Digital Input Modules

• 1756-IB16: 16-channel 24VDC sinking digital input
• 1756-IB32: 32-channel 24VDC sinking digital input, high-density
• 1756-IA16: 16-channel 120VAC digital input

Digital Output Modules

• 1756-OB16E: 16-channel 24VDC electronically fused sourcing digital output
• 1756-OB32: 32-channel 24VDC sourcing digital output, high-density

Controller Modules

• 1756-L85E: ControlLogix 5580 controller, 40MB memory, dual EtherNet/IP ports, CIP Security
• 1756-L83E: ControlLogix 5580 controller, 20MB memory, dual EtherNet/IP ports
• 1756-L71: ControlLogix 5570 controller, 2MB memory, single EtherNet/IP port

Communication Adapter Modules

• 1756-EN2T: Single-port EtherNet/IP communication module, 100Mbps
• 1756-EN2TR: Dual-port EtherNet/IP with Device Level Ring (DLR) support
• 1756-CN2R: Dual-port ControlNet communication module

Power Supply Modules

• 1756-PA75: 120/240VAC input power supply, 13A at 5VDC backplane output
• 1756-PB75: 18–32VDC input power supply, 13A at 5VDC backplane output

Sourcing Hard-to-Find & Obsolete ControlLogix 1756 Parts

Several modules within the 1756 series have reached end-of-life (EOL) or end-of-support (EOS) status as Rockwell Automation transitions customers toward the ControlLogix 5580 (L8x) platform. Modules including the 1756-IT6I, 1756-CN2R, and early L6x controller variants are no longer manufactured but remain in active service at facilities with 20–30 year operational lifecycles.

Quality Control for the ControlLogix 1756 Range

The 1756 backplane operates at 5VDC with a proprietary ControlBus protocol. Functional verification of 1756 modules requires chassis-level energization and controller communication — bench-level power application alone is insufficient to confirm module health. DriveKNMS performs the following verification steps for all 1756 inventory:

• Chassis insertion and backplane communication handshake verification using a reference 1756-L7x or L8x controller
• Channel-level I/O verification for analog modules using calibrated signal sources (Fluke 725 or equivalent)
• RTD simulation testing for 1756-IR12 and 1756-IT6I variants using decade resistance boxes across all 12 channels
• Firmware revision identification and compatibility mapping against current Logix Designer release matrix
• Visual inspection of backplane connector pins, module locking tabs, and status LED functionality
• 48-hour burn-in under simulated load conditions for controller and communication modules