Overview
The Allen-Bradley 1771-A3B /B is a 12-slot universal I/O chassis that serves as the mounting and backplane communication platform for the PLC-5 system. This chassis is designed to accommodate 1771-series I/O modules—including digital, analog, and specialty types—and supports both processor and I/O adapter modules for flexible centralized or distributed control architectures.
Key Features
- 12 I/O Slots: Provides installation locations for up to 12 modules, supporting flexible system expansion and modular design.
- Centralized Power Distribution: Delivers 24 Amperes maximum backplane current at 5 VDC for efficient power management across all installed modules.
- Dual Mounting Options: Supports 19-inch rack mounting and back-panel mounting, enabling versatile installation in different industrial enclosures.
- Universal Module Compatibility: Works seamlessly with all 1771-series input/output and specialty modules, allowing modular system design and easy field replacement.
- Series B Reliability: Enhanced performance and durability compared to earlier revisions for improved operational consistency.
Technical Specifications
- Backplane Voltage: 5 VDC
- Maximum Backplane Current: 24 Amperes @ 5.25 VDC
- Backplane Memory Line: 0.5 Amperes @ 5.25 VDC Max
- I/O Slot Count: 12 slots
- Physical Dimensions: 19.0 × 13.53 × 8.5 inches (483 × 339 × 221 mm)
- Weight: 19.1 lbs (5.9 kg)
- Operating Temperature: 0 to 60 °C (32 to 140 °F)
- Relative Humidity: 5–95% non-condensing
- Mounting: 19-inch rack mount or back-panel mount with mounting tabs
- Certifications: Class 1, Division 2, Groups A, B, C, and D
- Pollution Degree: 2
- Altitude: Up to 2000 meters without derating
Typical Applications
The 1771-A3B /B chassis is widely used in legacy PLC-5 control systems across manufacturing, process control, material handling, packaging, and discrete automation environments. It serves as the I/O distribution hub in centralized control architectures and supports remote I/O configurations via I/O adapter modules. Common applications include conveyor systems, bottling lines, assembly machines, and industrial machinery where modular I/O expansion is required.
Compatibility & Replacements
The 1771-A3B /B is compatible with all Allen-Bradley 1771-series I/O modules, including digital input/output (DI/DO), analog input/output (AI/AO), and specialty modules such as communication adapters and counter modules. Series A and earlier revisions perform similarly, though Series B offers enhanced reliability. Upgrade paths to larger chassis such as the 1771-A4B (16-slot) are available for systems requiring expanded I/O capacity. Always verify module compatibility with your specific processor module and control application requirements.
