Allen-Bradley 1756-L71 Logix5571 Controller – ControlLogix 1756 Series
When a ControlLogix controller fails mid-shift, the consequences are immediate and measurable: production lines halt, safety interlocks go into undefined states, and maintenance teams face unplanned downtime that can cost thousands of dollars per hour. In process-critical environments — automotive stamping, chemical batching, water treatment — the controller is not a peripheral component. It is the decision-making core of the entire control architecture. Without a verified replacement on hand, recovery time stretches from minutes into hours.
The 1756-L71 (catalog alias: Logix5571) occupies the mid-to-high tier of the ControlLogix 1756 platform, offering 2 MB of user memory — sufficient for complex motion sequences, multi-axis coordination, and large-scale process programs that exceed the capacity of the L61 or L62. Introduced as part of Rockwell Automation’s fifth-generation Logix controller family, the L71 has been deployed across tens of thousands of installations globally, making it one of the most widely supported PLCs in the industrial automation market. Its firmware ecosystem, Studio 5000 Logix Designer compatibility, and broad I/O module library ensure long-term maintainability for system integrators and end users alike.
Technical Specifications
Electrical
- Backplane Current Draw: 1.2 A @ 5 VDC; 3.0 mA @ 24 VDC
- Power Dissipation: 6.1 W (typical)
- Backplane Communication: ControlBus (proprietary high-speed backplane)
Processing & Memory
- User Memory: 2 MB (2,097,152 bytes)
- I/O Memory: 478 KB
- Tasks: Up to 32 (1 continuous, 31 periodic/event)
- Programs per Task: Up to 100
- Motion Axes: Up to 100 (coordinated motion)
- Communication Connections: Up to 256
Mechanical
- Form Factor: Single-slot ControlLogix chassis module
- Dimensions: 94.0 mm H × 34.5 mm W × 128.3 mm D (approximate)
- Weight: Approx. 0.4 kg
- Mounting: 1756 ControlLogix chassis (4, 7, 10, 13, or 17-slot)
Environmental
- Operating Temperature: 0 °C to 60 °C
- Storage Temperature: −40 °C to 85 °C
- Relative Humidity: 5% to 95% (non-condensing)
- Vibration: 2 g @ 10–500 Hz (IEC 60068-2-6)
- Shock: 30 g operational (IEC 60068-2-27)
Certifications
- UL Listed, CE Marked, RCM, KC
- ATEX / IECEx: Zone 2 (with appropriate enclosure)
- Industry Standard: IEC 61131-3 (all five programming languages supported)
Key Features & Benefits
- 2 MB User Memory — Accommodates programs exceeding 500,000 rungs of ladder logic or equivalent structured text, eliminating the need to partition large applications across multiple controllers.
- Up to 100 Coordinated Motion Axes — Supports CIP Motion over EtherNet/IP, enabling synchronized multi-axis control without a dedicated motion controller, reducing panel footprint and wiring complexity.
- IEC 61131-3 Compliant Programming — Full support for Ladder Diagram, Function Block Diagram, Structured Text, Sequential Function Chart, and Instruction List; engineers can mix languages within a single project.
- Nonvolatile Memory (SD Card Slot) — Program and firmware stored on removable SD card; replacement controller can be restored to full operation in under 5 minutes without a programming terminal on-site.
- Integrated Diagnostics — Controller-level fault logging with timestamped entries; reduces mean time to diagnose (MTTD) by providing engineers with a structured fault history rather than anecdotal operator reports.
- EtherNet/IP Producer/Consumer Model — Deterministic peer-to-peer data exchange between controllers at configurable RPI rates as low as 1 ms, supporting tight inter-controller synchronization in distributed architectures.
Industry & Equipment Applications
- Automotive Manufacturing — Body-in-white welding lines, transfer press sequencing, paint shop conveyor control, and end-of-line test stations requiring coordinated multi-axis motion.
- Oil & Gas — Wellhead control panels, pipeline SCADA RTU replacement, compressor station automation, and emergency shutdown (ESD) systems where SIL-rated logic is managed alongside standard process control.
- Food & Beverage — CIP (Clean-in-Place) sequence control, filling and capping machine coordination, pasteurization temperature loop management, and batch recipe execution per ISA-88.
- Water & Wastewater Treatment — Pump station control, SCADA integration via DNP3 or Modbus TCP, chemical dosing automation, and distributed lift station management.
- Pharmaceutical — FDA 21 CFR Part 11-compliant batch control, clean room HVAC sequencing, lyophilizer process control, and serialization line integration.
- Power Generation & Utilities — Turbine auxiliary control, substation automation, load-shedding logic, and integration with DCS systems via OPC-UA or EtherNet/IP bridging.
System Integration & Compatible Parts
Required Upstream Components:
- 1756-Axx ControlLogix Chassis (4, 7, 10, 13, or 17-slot)
- 1756-PAxx or 1756-PBxx Power Supply (matched to chassis)
- 1756-EN2T / 1756-EN2TR EtherNet/IP Communication Module (for network connectivity)
Compatible I/O Modules (downstream):
- 1756-IB16 / 1756-OB16E Digital I/O
- 1756-IF8 / 1756-OF8 Analog I/O
- 1756-M02AE / 1756-M08SEG Motion Modules
Programming Software:
- Studio 5000 Logix Designer v21.00 and above (RSLogix 5000 v20 for legacy firmware)
Equivalent / Substitute Models:
- 1756-L72 — 4 MB variant; direct form-fit-function replacement when additional memory is required; same firmware revision compatibility.
- 1756-L73 — 8 MB variant; recommended for applications with large Add-On Instruction (AOI) libraries or extensive HMI tag databases.
- 1756-L61 — 2 MB predecessor (Series A/B); functionally similar but limited to older firmware; not recommended for new installations.
Note: Substitution between L7x and L6x series requires firmware migration and project re-compilation. Always verify firmware compatibility before substituting.
Our Quality Assurance Process
Every 1756-L71 unit sourced and shipped by Konmask.com passes a four-stage inspection protocol before dispatch:
- Visual & Physical Inspection — Housing integrity, connector pin condition, label legibility, and serial number verification against manufacturer records.
- Firmware & Revision Verification — Firmware version confirmed and documented; Series revision (A, B, C) recorded and disclosed in the quotation.
- Functional Power-On Test — Unit powered in a 1756 chassis with a matched power supply; LED status indicators, backplane communication, and self-diagnostic routines verified.
- ESD-Safe Packaging & Documentation — Shipped in anti-static packaging with desiccant; accompanied by inspection report, test record, and available certificates of conformance (CoC) or factory test reports upon request.
Available Documentation: Inspection Report · Certificate of Conformance · Firmware Revision Record · Rockwell Automation Traceability (where available) · Customs Commercial Invoice
How to Order
- Submit Your Inquiry — Use the contact form on this page or email support@konmask.com with your required quantity, target delivery date, and any firmware revision preferences.
- Receive Quotation — Our technical team will confirm stock availability, unit condition (new / surplus / refurbished), firmware revision, and pricing within 24 hours on business days.
- Confirm & Ship — Upon order confirmation, units are inspected, packed, and dispatched with full documentation. Express and standard international shipping options available.
Why Choose Konmask.com?
- Verified Stock, Disclosed Condition — We clearly state whether units are new-in-box, surplus, or refurbished. No ambiguity, no surprises on arrival.
- Technical Pre-Sales Support — Our team includes engineers with hands-on ControlLogix experience who can advise on firmware compatibility, chassis sizing, and integration requirements before you commit to a purchase.
- Global Shipping with Export Documentation — We ship to over 60 countries with full commercial invoice, packing list, and country-of-origin documentation to support customs clearance.
- Responsive Communication — 24-hour quotation turnaround on business days; dedicated account management for repeat buyers and system integrators.
- Long-Term Parts Sourcing — Specializing in both current-production and discontinued Rockwell Automation catalog numbers, supporting legacy system maintenance without forced upgrades.
Frequently Asked Questions
Q: What is the difference between the Allen-Bradley 1756-L71 and 1756-L72 ControlLogix controller?
A: The primary difference is user memory: the 1756-L71 provides 2 MB while the 1756-L72 provides 4 MB. Both share the same chassis slot, power requirements, firmware architecture, and Studio 5000 compatibility. If your application involves large AOI libraries, extensive HMI tag databases, or programs approaching the 2 MB limit, the L72 is the recommended upgrade path — it is a direct drop-in replacement with no hardware changes required.
Q: Can I use a surplus or refurbished 1756-L71 in a production environment, and what firmware version will it have?
A: Yes, surplus and refurbished ControlLogix controllers are widely used in production environments when sourced from a reputable supplier with documented inspection. Firmware version varies by unit history; Konmask.com discloses the firmware revision in every quotation. Firmware can be upgraded using Studio 5000 / ControlFLASH if a specific version is required — we can advise on the upgrade path for your target version.
Q: What ControlLogix chassis and power supply are compatible with the 1756-L71 for a new panel build?
A: The 1756-L71 fits any 1756-series ControlLogix chassis (4-slot 1756-A4, 7-slot 1756-A7, 10-slot 1756-A10, 13-slot 1756-A13, or 17-slot 1756-A17). Pair it with a 1756-PA72 (120/240 VAC) or 1756-PB72 (24 VDC) power supply for standard applications. For redundant power configurations, the 1756-PSCA2 chassis adapter supports dual power supply modules. We can provide a complete BOM for your chassis configuration upon request.
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