The Allen-Bradley 1747-L532 is a widely recognized PLC CPU module from the SLC 500 family. Known as part of the SLC 5/03 series, it balances power, flexibility, and cost-effectiveness, making it one of the most trusted controllers in industrial automation history. In this extended blog, we’ll explore its detailed specifications, break down what each feature means, look at real-world industry applications, and provide insights into lifecycle management and comparisons with newer systems.
Our focus keyword throughout this blog is Allen-Bradley 1747-L532, ensuring readers searching for this CPU find the right information.
Introduction to the Allen-Bradley 1747-L532
The Allen-Bradley 1747-L532 processor is part of Rockwell Automation’s SLC 500 family of mid-range PLCs, offering control power suitable for manufacturing, packaging, process industries, and infrastructure automation. It supports 16K words of memory, DH-485 and RS-232 communication, and up to 4096 I/O points across local and remote modules. With a scan time of 1 ms per 1K instructions, it can manage time-critical processes with precision.
The importance of this CPU lies in its versatility: it can be deployed in high-speed discrete manufacturing systems, process plants requiring analog control, and even infrastructure projects like water and energy systems.
Historical Context of the SLC 500 Family
To understand the Allen-Bradley 1747-L532, we should look at the SLC 500 family’s history. The SLC series was introduced in the 1990s to provide a modular, scalable alternative between the smaller MicroLogix series and the larger PLC-5 controllers. The SLC 5/03 processors like the 1747-L532 became popular because they provided faster scan rates, built-in networking (DH-485), and larger memory compared to the earlier SLC 5/01 and 5/02.
The SLC 500 family paved the way for modern modular PLC design, influencing successors like the CompactLogix and ControlLogix platforms. While newer PLCs have Ethernet/IP and larger capacities, the 1747-L532 still finds use in many legacy systems worldwide.
Detailed Specifications of the Allen-Bradley 1747-L532
Memory: 16K Words
The Allen-Bradley 1747-L532 comes with 16K words of memory, divided into program and data storage. This allows engineers to store:
● Ladder logic programs with advanced instructions
● Timers, counters, and control logic
● Data tables for process variables and setpoints
Why it matters: More memory supports complex processes, ensuring users can expand their automation without running into limitations.
Communication Ports: DH-485 and RS-232
● DH-485 Port: A multi-drop network link for PLC-to-PLC communication and remote I/O expansion.
● RS-232 Port: Supports DF1 protocols and ASCII mode for PC programming, HMIs, and external devices like printers.
Why it matters: Integrated communication reduces the need for additional modules and enables seamless connection between controllers, operator terminals, and monitoring systems.
I/O Capacity: 960 Local and 4096 Remote
Locally, the 1747-L532 can handle up to 960 I/O points across three chassis. With expansion networks, it scales up to 4096 I/O points.
Why it matters: High I/O capacity enables the CPU to manage large systems with thousands of field devices, making it suitable for distributed manufacturing plants and complex process control systems.
Scan Rate: 1 ms per 1K Instructions
The 1 ms scan time per 1000 instructions ensures fast program execution. Additional features include:
● STI (Selectable Timed Interrupts) – precise, scheduled task execution.
● DII (Discrete Input Interrupts) – immediate response to input changes.
Why it matters: Time-sensitive applications like high-speed packaging benefit from rapid response times.
Power Requirements: 5VDC and 24VDC
The CPU draws:
● 500 mA at 5VDC
● 175 mA at 24VDC
Why it matters: Proper power budgeting ensures reliable system operation, especially when multiple I/O modules share the same backplane.
Additional Features
● Real-time clock/calendar for scheduling
● Firmware stored in flash for easy updates
● Online editing without halting production
● RUN/REMOTE/PROGRAM key switch for operator control
Why it matters: These features maximize uptime and allow for flexible and safe system adjustments.
Industry Applications of the Allen-Bradley 1747-L532
Packaging and Material Handling
The fast scan rate and interrupts make the Allen-Bradley 1747-L532 ideal for conveyor lines, labeling systems, and high-speed packaging where precise timing is crucial.
Discrete Manufacturing
In automotive and electronics production, the CPU manages motors, sensors, and actuators with high reliability, coordinating assembly lines and robotics.
Continuous Process Industries
Chemical plants, batch processing systems, and water treatment facilities rely on the L532 for its PID capabilities and ability to handle analog I/O.
Utilities and Infrastructure
Pump stations, water distribution, and power systems benefit from its reliability, scheduling, and communication options.
Comparison with Other PLCs
● SLC 5/01 & 5/02: The 1747-L532 is faster and offers more memory and communication ports.
● SLC 5/04: Provides DH+ communication but no DH-485, targeting larger systems.
● CompactLogix & ControlLogix: Newer systems with Ethernet/IP, higher memory, and faster processing, but at a higher cost.
Why it matters: The 1747-L532 remains relevant for legacy systems where replacing the entire architecture is impractical.
Lifecycle and Maintenance
The Allen-Bradley 1747-L532 has been placed in Rockwell’s “Silver” lifecycle phase, meaning it’s still supported but not actively developed. Users must plan for:
● Spare part management – keeping replacement CPUs on hand
● Migration planning – considering upgrades to CompactLogix/ControlLogix
● Firmware updates – applying the latest supported revisions
Why it matters: Proper lifecycle management ensures continued reliability and avoids costly downtime when components reach obsolescence.
Case Studies and Real-World Examples
Food & Beverage Packaging
A bottling plant uses the 1747-L532 to control conveyors, filling stations, and labeling machines. Its fast scan and interrupts ensure bottles are filled and labeled with precision.
Automotive Assembly
In an automotive facility, the CPU coordinates robotic arms and conveyors, handling hundreds of sensors and actuators while ensuring precise synchronization.
Water Treatment Plant
The real-time clock and analog I/O capabilities make it ideal for dosing chemicals, monitoring water quality sensors, and running timed valve operations.
Why Engineers Still Choose the Allen-Bradley 1747-L532
● Proven reliability in harsh environments
● Wide installed base for spare parts and expertise
● Flexible I/O expansion and communication
● Cost-effective for legacy system maintenance
Conclusion
The Allen-Bradley 1747-L532 stands as a testament to Rockwell’s durable and flexible automation design. While newer systems now dominate, this CPU continues to serve as the backbone of countless plants worldwide. With its balance of memory, communication, I/O capacity, and speed, it remains a trusted controller in industries that value uptime and reliability.
If you’d like to explore further details, including datasheets, manuals, or replacement options, visit the Allen-Bradley 1747-L532 product page and see how this classic PLC can support your operations today.
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