How Do Allen Bradley CompactLogix and ControlLogix PLCs Differ?
1. Architectural & Performance Data Comparison
CompactLogix 5380/5480 Series 1756-PA75 is built on an integrated, fixed-I/O architecture. The system resides in a single housing with embedded I/O, communications, and power supply. It supports a maximum local I/O capacity of approximately 500 to 1,000 points via add‑on modules, limited by its embedded communication ports. Controller memory ranges from 10 MB to 32 MB for user program and data. Its logic execution speed is approximately 0.08 ms per kilobyte of instruction for a typical 5380 controller. It features one to two embedded EtherNet/IP ports (10/100/1000 Mbps) and is limited to installing only two to four communication adapters. The system does not support hardware redundancy, operates with a typical power consumption of 15-40 watts, and functions within a standard 0-60°C temperature range.
ControlLogix 5580/5585 Series 1756-IB32 employs a modular rack system with separate chassis (4‑18 slots) for power supply, CPU, communication, and I/O modules. It offers a vastly superior maximum local I/O capacity of up to approximately 128,000 connections across multiple chassis. Controller memory is significantly larger, ranging from 100 MB to over 2 GB. It executes logic nearly twice as fast as comparable CompactLogix models, at about 0.04 ms/K instruction for a typical 5580 CPU. Unlike CompactLogix, it has no embedded ports; all communication is handled by dedicated module cards, allowing for a virtually unlimited number of installed communication modules. It supports full hardware redundancy with a switchover time of ≤50 milliseconds. Typical power consumption is higher, from 50 to over 200 watts, and it operates in a 0-60°C range with better derating for harsh environments.
2. Total Cost of Ownership (TCO) & Application Data
The initial hardware cost (CAPEX) for a CompactLogix system typically ranges from $2,000 to $8,000 for a controller with basic I/O. Its panel footprint is 60-80% smaller than a modular system, significantly reducing enclosure costs. Wiring is simplified due to integrated I/O. However, its diagnostic capabilities are more limited. It is ideally suited for machines with 500 or fewer I/O points, eight or fewer motion axes, and cycle times no faster than 20 milliseconds.
In contrast, the initial cost for a ControlLogix system 1756-TBCH starts at $8,000 to $15,000 for a base chassis, CPU, and power supply, and can exceed $30,000 for redundant, high‑performance configurations. Its modular design supports the hot‑swapping of I/O modules without shutting down the CPU, reducing Mean Time To Repair (MTTR). Its advanced module‑level and channel‑level diagnostics can improve system reliability, increasing Mean Time Between Failures (MTBF) by 15-25% in complex installations. This platform is designed for systems with over 1,000 I/O points, 16 or more synchronized motion axes, and cycle times of 10 milliseconds or less.
3. Comparison with Key Competitors
When compared to Siemens, the CompactLogix faces strong competition from the S7-1200, which offers a 20-30% lower cost for similar I/O counts, and the S7-1500, which provides higher performance per dollar and more built‑in functions like an integrated OPC UA server. Against ControlLogix, the Siemens S7-1500 offers comparable performance at a 10-20% lower hardware cost and superior engineering integration within the TIA Portal, though it lacks native hardware redundancy in its standard CPU offerings.
Against Schneider Electric, the CompactLogix competes with the Modicon M580 Premium, which offers higher I/O density and more embedded communication options. When compared to ControlLogix, the Modicon M580 provides comparable modularity and performance with native support for both EtherNet/IP and Modbus TCP, though its redundancy solutions are generally considered less mature than Rockwell's.
Compared to GE/Emerson's PAC Systems, the CompactLogix alternative is the RX3i, which often has a 15-25% lower cost but a smaller support ecosystem. The ControlLogix competitor is the RX7i, which offers comparable high‑availability and redundancy, particularly in the power and energy sectors, but has less market penetration in discrete manufacturing.
4. Decision Matrix: Quantitative Selection Guide
The choice between platforms is dictated by clear quantitative thresholds. Choose CompactLogix if your application has fewer than 500 I/O points, requires eight or fewer motion axes, can tolerate downtime exceeding one hour, needs only one or two network types, has limited panel space (less than 1 m²), a hardware budget under $15,000, and a low anticipated growth of less than 20% in five years.
Choose ControlLogix if your system requires more than 1,000 I/O points, 16 or more synchronized motion axes with precision under 5 milliseconds, mandates hardware redundancy due to high downtime costs (exceeding $10,000 per hour), needs three or more different industrial networks, has an unrestricted panel space, a project hardware budget over $25,000, and a high anticipated growth of more than 50% in five years.
5. Conclusion: Data‑Defined Divergence
The decision between CompactLogix and ControlLogix 1794 ib32 is a strategic one, defined by measurable data. CompactLogix is the cost‑ and space‑optimized solution for discrete machines with bounded I/O, no redundancy requirements, and a focus on initial capital efficiency. ControlLogix is the high‑performance, scalable platform for process‑critical or large‑scale systems requiring extensive I/O, hardware redundancy, multi‑network integration, and long‑term flexibility. Its higher initial cost is justified by a lower total lifecycle cost in complex, expanding applications. Both families are unified under the Studio 5000 Logix Designer environment, protecting software investments and enabling strategic migration, which reduces global training and maintenance costs for enterprises deploying both PLC types.
Tsuen Wan,HONG KONG
