Description
The Allen-Bradley 1785-L40E (often denoted 1785-L40E/A for Series A) is a PLC-5/40E EtherNet/IP programmable controller designed for medium to large-scale industrial automation. As part of the classic PLC-5 family, it combines a 48K word battery-backed RAM processor with native 10/100 Mbps Ethernet and dual DH+/Remote I/O ports. This module is installed in a 1771 I/O chassis and serves as the central control unit for discrete and analog I/O systems, supporting up to 4096 I/O points (2048 inputs + 2048 outputs) across local and remote racks.
Application Scenarios
In a water treatment plant, the 1785-L40E acts as the main process controller for a filtration and pumping station. The processor’s EtherNet/IP port communicates with a SCADA system for real-time monitoring, while its DH+ port connects to legacy PanelView terminals on the plant floor. The Remote I/O scanner function manages distributed 1771 analog modules (e.g., 1771-IFE) for flow and pressure monitoring, and 1771 digital modules for pump control. The system uses PID instructions to maintain precise chemical dosing rates based on analog feedback.
Parameter
| Parameter | Specification |
|---|---|
| Manufacturer | Rockwell Automation (Allen-Bradley) |
| Model | 1785-L40E / 1785-L40E/A (Series A) |
| Product Type | PLC-5/40E EtherNet/IP Programmable Controller |
| User Memory | 48K Words (Battery-Backed Static RAM) |
| Memory Backup | Optional EEPROM (1785-ME16, ME32, ME64, M100) |
| Max Discrete I/O | 2048 (any mix) or 2048 In + 2048 Out (Complementary) |
| Max Analog I/O | 2048 |
| I/O Chassis Capacity | Up to 61 chassis (1 local + 60 remote) |
| Communication Ports | 2x DH+/Remote I/O (Adapter/Scanner), 1x RS-232/422/423 Serial, 1x Ethernet (10/100 Mbps, TCP/IP) |
| Backplane Current | 3.3 A @ 5V DC |
| Power Dissipation | 17.3 W |
| Battery | 1770-XYC (Lithium, pre-installed) |
| Operating Temperature | 0°C to 60°C (32°F to 140°F) |
| Compatible Chassis | 1771-A1B, A2B, A3B, A3B1, A4B |
| Programming Software | RSLogix 5, AI-5, PLC-5 Programming Software |
Technical Principles and Innovative Values
The 1785-L40E represents a significant evolution in the PLC-5 series by integrating EtherNet/IP connectivity directly into the processor module, a feature previously requiring a separate 1785-ENET interface card.
- Innovation Point 1: Integrated EtherNet/IP Stack. Unlike earlier PLC-5 models that relied on external communication modules, the 1785-L40E incorporates a native TCP/IP protocol stack and 10/100 Mbps Ethernet port. This allows the controller to communicate directly with modern HMIs, SCADA systems, and other Ethernet-enabled devices without additional hardware, simplifying network architecture and reducing latency for peer-to-peer messaging.
- Innovation Point 2: Multi-Network Gateway Capability. The processor functions as a network bridge between legacy and modern systems. Its dual DH+/Remote I/O ports can operate simultaneously with the Ethernet port, enabling seamless integration of older Data Highway Plus (DH+) networks (e.g., connecting to SLC 5/04 controllers or PanelView 550s) while providing a migration path to Ethernet-based control.
- Innovation Point 3: Deterministic I/O Scanning. The 1785-L40E utilizes a hardware-based I/O scanner for Remote I/O (RIO) networks. It supports block transfer (BT) operations for intelligent I/O modules (e.g., analog, high-speed counter) and offers configurable scan times as low as 0.5 ms for extended-local I/O, ensuring deterministic control of high-speed processes independent of the program scan time.
