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- Allen Bradley
- 1785-L40B
- PLC-5/40 Processor
- USA
- 165 x 51 x 89 mm
- 1.42 kg
- Xiamen, China
- New & In Stock
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Product Overview
The Allen-Bradley 1785-L40B is a PLC-5/40 processor module from Rockwell Automation, used in the classic PLC-5 programmable controller family. It serves as the central CPU of a PLC-5 system, responsible for executing control logic, managing I/O, and handling industrial communication networks such as DH+ and remote I/O.
This model is widely used in legacy industrial automation systems and supports medium-to-large control applications.
Technical Specifications
| Parameter | Details |
|---|---|
| Manufacturer | Allen-Bradley (Rockwell Automation) |
| Model | 1785-L40B |
| Product Type | PLC Processor Module |
| System Series | PLC-5 |
| Memory | 48K words user memory |
| I/O Capacity | Up to ~2048 I/O points (system dependent) |
| Communication Ports | DH+, Remote I/O, serial (RS-232/RS-422/RS-423) |
| Backplane Load | 5 V DC, approx. 3.3 A |
| Max I/O Chassis | Up to 61 (system dependent) |
| Programming | Ladder Logic, SFC, structured programming support |
| Installation | 1771 I/O chassis |
| Dimensions | 165 × 51 × 89 mm |
| Weight | 1.42 kg |
Function and Working Principle
The 1785-L40B acts as the central processing unit of a PLC-5 system.
Its core functions include:
- Executing user control programs (ladder logic)
- Managing input/output scanning cycles
- Handling industrial network communication (DH+, remote I/O)
- Coordinating data exchange between modules
- Controlling machine and process automation tasks
It continuously cycles through input scan → program execution → output update, enabling real-time industrial control.
Key Features
- High-capacity PLC-5/40 processor
- Supports multiple industrial communication protocols
- Reliable real-time control processing
- Modular chassis-based architecture
- Suitable for large-scale industrial systems
- Strong diagnostic and status indication features
Industrial Applications
- Factory automation systems
- Chemical and petrochemical plants
- Power generation systems
- Manufacturing production lines
- Water and wastewater treatment systems
- Heavy industrial machinery control
Role in Industrial Systems
The module serves as the central controller of PLC-5 architectures, responsible for:
- Running automation logic
- Coordinating multiple I/O racks
- Managing network communication
- Ensuring real-time process control stability
It is a key component in legacy Allen-Bradley automation infrastructure.
Installation Notes
- Installed in a 1771 PLC-5 chassis
- Requires compatible power supply module (e.g., 1771-P series)
- Proper backplane seating is critical
- Battery backup may be required for program retention
- DIP switches or configuration tools used for setup
Compatible Equipment
- 1771 I/O chassis systems
- PLC-5 I/O modules
- DH+ communication networks
- Remote I/O modules and adapters
- Allen-Bradley industrial control systems
Advantages
- Reliable and proven industrial CPU
- Strong communication capability for legacy systems
- Suitable for large-scale automation
- Long operational lifespan in industrial environments
- Stable real-time control performance
Limitations
- Obsolete / legacy system (no longer mainstream)
- Not compatible with modern ControlLogix platforms
- Limited modern networking support
- Requires specialized maintenance knowledge
Conclusion
The Allen-Bradley 1785-L40B PLC-5/40 Processor is a robust legacy PLC CPU designed for industrial automation systems requiring reliable real-time control and DH+/remote I/O communication.
It remains widely used in existing installations where PLC-5 infrastructure is still in operation.