The Allen-Bradley 1756-A4 is a ControlLogix chassis from Rockwell Automation used in the ControlLogix PLC system. It provides the physical rack and high-speed backplane needed to mount and connect ControlLogix controllers, I/O modules, and communication modules.
It does not perform control logic itself—its role is to act as the hardware backbone that distributes power and enables communication between modules in an industrial automation system.
This chassis is commonly used in compact PLC systems where only a small number of modules are required.
Key Features
- 4-slot ControlLogix chassis
- High-speed backplane communication
- Horizontal rack mounting
- Supports any ControlLogix module type
- Modular expansion via additional chassis
- Open-style industrial rack design
Technical Specifications
| Parameter | Details |
|---|---|
| Product Type | ControlLogix Chassis |
| Model | 1756-A4 |
| Manufacturer | Allen-Bradley (Rockwell Automation) |
| Number of Slots | 4 |
| Backplane Function | Power + communication bus |
| Mounting Type | Horizontal only |
| Enclosure Type | Open rack |
| Power Dissipation | ~1.8 W |
| Backplane Voltage | 1.2 V / 3.3 V / 5.1 V / 24 V DC |
| Operating Temperature | 0°C to 60°C |
| Storage Temperature | -40°C to 85°C |
Physical Dimensions & Weight
| Specification | Value |
|---|---|
| Height | ~158 mm |
| Width | ~263 mm |
| Depth | ~145 mm |
| Overall Envelope (typical panel space) | ~508 × 508 × 203 mm |
| Weight | ~0.8–1.0 kg (chassis only) |
The chassis is compact and designed for installation inside industrial control cabinets.
Function in ControlLogix System
The 1756-A4 serves three core roles:
- Mechanical mounting platform for PLC modules
- Electrical backplane for communication between modules
- Power distribution bus for all installed cards
All modules inserted into the chassis communicate through the backplane, eliminating the need for external wiring between them.
Typical Modules Installed
A 1756-A4 chassis may include:
- ControlLogix CPU (e.g., 1756-L7x / L8x series)
- Digital input modules
- Digital output modules
- Analog I/O modules
- Communication modules (EtherNet/IP, ControlNet)
- Safety modules (SIL applications)
