1785-L40C15 F-2 1785-L40C15 F-3 1785-L40C15 F-1 1785-L40C15 F-4

The Allen-Bradley 1785-L40 is a PLC-5/40 standard processor CPU module designed for large-scale industrial automation and process control applications. As part of Rockwell Automation’s PLC-5 family, it delivers high processing capacity, expanded memory, and strong communication flexibility for complex distributed control systems.

This controller is widely used in heavy manufacturing, material handling, and legacy plant automation environments where long-term system stability and proven PLC architecture are critical for continuous operation.

Technical Specifications (including Dimensions & Weight)

Parameter	Specification
Product Type	PLC-5/40 Processor CPU Module
Series	PLC-5
Processor Type	Standard Processor
User Memory	48 Kilowords SRAM
Memory Backup	Battery-backed SRAM
EEPROM Support	1785-ME16 / ME32 / ME64 / M100
Communication Ports	2 × DH+ / Remote I/O + 1 × Serial (RS-232/422/423)
Max Total I/O	Up to 2048 points (any mix)
Max Analog I/O	2048
Max I/O Chassis	Up to 61
Remote I/O Capability	Supported
Backplane Current	~2.3 A @ 5V DC
Power Dissipation	~12 W
Installation	1771 PLC-5 Chassis
Operating Temperature	0°C to 60°C

Physical Dimensions & Weight

Item	Value
Size (L × W × H)	280 × 140 × 50 mm
Weight	~1.1–1.3 kg

Recommended Related Models

1785-L30B – mid-range PLC-5/30 processor module
1785-L20B – standard PLC-5/20 controller
1785-L11B – entry-level PLC-5/11 CPU module
1785-ENET – Ethernet communication module for PLC-5
1784-PCIC – PCI communication interface module

Popular Allen-Bradley Models

1756-L81E ControlLogix Processor Module
1769-L33ER CompactLogix Controller
1756-EN2T EtherNet/IP Communication Module
1734-AENT POINT I/O Adapter
1794-ACN Flex I/O Communication Adapter

Applications

The 1785-L40 is commonly deployed in:

Large-scale PLC-5 industrial automation systems
Manufacturing process control environments
Distributed remote I/O architectures
Conveyor and material handling systems
Packaging and production line automation
Brownfield modernization and retrofit projects

Its higher memory capacity and expanded I/O handling make it suitable for more complex control logic and larger plant-wide automation networks.

Advantages

High 48K-word memory for complex control programs
Strong support for distributed Remote I/O systems
Dual DH+ / Remote I/O communication channels
Stable performance for continuous industrial operation
Supports large-scale multi-chassis PLC architectures
Reliable battery-backed SRAM for data protection
Proven long-life PLC-5 architecture
Ideal for legacy plant expansion and maintenance

Technical FAQs

1. What is the 1785-L40 used for?
It is a high-capacity PLC-5 processor for industrial automation control.

2. How much memory does it have?
It provides 48K words of SRAM user memory.

3. How many I/O points can it handle?
Up to 2048 total I/O points depending on system configuration.

4. Does it support DH+ communication?
Yes, it includes DH+ and Remote I/O communication capability.

5. What chassis does it use?
It installs into a 1771 PLC-5 chassis system.

6. Is the memory battery-backed?
Yes, SRAM memory is protected by a backup battery.

7. Can it support distributed I/O systems?
Yes, it supports extensive Remote I/O architectures.

8. Is it still manufactured today?
No, it is a legacy PLC-5 product line module.

9. What replaced PLC-5 systems?
Modern ControlLogix platforms such as the 1756 series.

10. Why is it still used in industry?
Many industrial facilities still rely on PLC-5 systems for stable long-term production operations.

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Allen Bradley PLC

Allen-Bradley 1785-L40 PLC-5/40 Processor CPU Module