Overview
The Allen-Bradley 1794-ASB2 is a FLEX I/O remote I/O adapter manufactured by Rockwell Automation. This module functions as a communication bridge and power supply for distributed FLEX I/O systems, converting 24VDC to 5VDC for internal backplane logic. The 1794-ASB2 supports connection of up to 2 FLEX I/O modules over Remote I/O (RIO) link, making it essential for modular, scalable distributed control architectures in manufacturing, process control, and industrial automation environments.
Key Features
- Dual I/O Module Capacity: Supports 2 FLEX I/O modules, ideal for compact distributed I/O systems with limited space requirements.
- Multiple Baud Rates: Configurable communication at 57.6 Kbps, 115.2 Kbps, or 230.4 Kbps for flexible network integration.
- 24VDC Nominal Power: Requires external 24VDC power supply with 23 A inrush current capability (2 ms duration).
- Status Indicators: Red/green LED indicators display adapter, power, and local connection status for quick diagnostics.
- DIN Rail Mounting: Open-style enclosure design mounts directly to standard DIN rail for field deployment.
- Industrial Certification: UL Listed for Class I, Division 2 hazardous locations (Groups A–D) and general industrial control equipment.
Technical Specifications
Input voltage range: 19.2–31.2 VDC (nominal 24VDC) | Isolation voltage: 500VAC (power-to-system, power-to-RIO, RIO-to-system, type-tested at 750VDC for 60 seconds) | Output: 5VDC @ 640 mA maximum | Current draw: 330–450 mA @ 24VDC | Power consumption: 4.2 W @ 24VDC | Thermal dissipation: 1.7 BTU/hr @ 31.2VDC | Communication: RIO Link (57.6–230.4 Kbps) | Connector: FlexBus standard | Mounting: DIN rail (3.4 × 2.7 × 2.7 inches) | Weight: 0.4 lbs | Wire gauge: 22–12 AWG or 22–16 AWG (75 °C rated minimum)
Typical Applications
- Distributed I/O Architecture: Connect remote I/O racks to PLC-5 processors across extended distances via RIO communication link.
- Plant Floor Automation: Deploy modular control at machine stations, assembly lines, and production cells requiring local I/O proximity.
- Hazardous Area Control: Class I, Division 2 certification enables use in environments with potentially explosive atmospheres (oil/gas facilities, chemical plants).
- Legacy System Integration: Drop-in replacement for obsolete or failed adapters in existing FLEX I/O installations.
Compatibility & Replacements
The 1794-ASB2 is compatible with PLC-5 processors supporting remote I/O communication. Important: This adapter must not be used with classic PLC-5/15 or PLC-5/25 processors, as improper operation and remote I/O damage may result. The 1794-ASB2 is discontinued by manufacturer but remains available through surplus and recertified channels. Related adapters in the 1794 FLEX series include the 1794-ASB (8-module capacity) and 1794-ASBLT (PLC-5/15 and PLC-5/25 compatible variant). For modern ControlLogix systems, Rockwell offers native remote I/O modules within the CompactLogix and ControlLogix families as forward replacements.
