Purchase now: Allen Bradley 1747-BSN Backup Scanner Module
Purchase now: Atlantechdrives provides you the 1747-BSN, a specialized Backup Scanner Module engineered by Allen Bradley specifically for the SLC 500 programmable logic controller family. In mission-critical industrial applications—such as continuous chemical processing, glass manufacturing, or municipal water treatment—a single point of failure in the control system can result in catastrophic product loss or severe safety hazards. The 1747-BSN mitigates this risk by enabling a «Hot-Backup» redundant architecture. By installing one 1747-BSN in a primary SLC chassis and a complementary 1747-BSN in a secondary (backup) SLC chassis, you create a synchronized pair. These modules communicate continuously via a high-speed Local Status Link (LSL). If the primary processor experiences a hardware fault, a power failure, or a critical network loss, the 1747-BSN instantly transfers control to the secondary processor. This switchover happens seamlessly, ensuring that your Remote I/O (RIO) network and connected field devices continue operating without interruption.
Technical Specifications of the 1747-BSN
The 1747-BSN provides backup functionality for Data Highway Plus (DH+) or Remote I/O (RIO) networks. It occupies a single slot in the 1746 chassis and is configured via software to define its role as primary or secondary in the redundant pair.
- Part Number: 1747-BSN
- Module Type: Backup Scanner Module
- Compatible Processors: SLC 5/02, 5/03, 5/04, 5/05
- Network Backup: Remote I/O (RIO) and Data Highway Plus (DH+)
- Communication Backup: RS-232 / DH-485 serial links
- Synchronization: High-speed Local Status Link (LSL)
- Backplane Current Draw: 800 mA at 5V DC
Expert Tips: Understanding Local vs. Remote I/O in Redundancy
The most common architectural mistake engineers make when designing a hot-backup system with the 1747-BSN is placing critical I/O cards in the local chassis. Expert Tip: The 1747-BSN module only backs up and transfers control of Remote I/O (RIO) chassis. Any standard digital or analog input/output modules located in the same physical chassis as the primary SLC processor (the Local I/O) are NOT backed up. If the primary processor fails and the system switches to the secondary chassis, the secondary processor cannot access the physical I/O cards left behind in the primary rack. For a true hot-backup system, your primary and secondary chassis should only contain processors, communication cards, and the BSN modules. All physical field wiring must be routed to remote adapter chassis (like the 1747-ASB) connected via the blue hose RIO network.
Maintenance: Testing the Switchover Mechanism
To ensure your redundancy system will actually protect you during an emergency, you must perform regular switchover tests during scheduled maintenance windows. You can manually trigger a switchover by forcing the primary processor into PROG mode, or by disconnecting the primary RIO network cable. Verify that the secondary processor assumes control smoothly and that no critical valves or motors drop out during the transition. Also, regularly inspect the serial Local Status Link (LSL) cable connecting the two BSN modules; if this cable is damaged, the redundancy will fail.
Frequently Asked Questions (FAQs)
Q: Can I use the 1747-BSN with a MicroLogix or ControlLogix system?
A: No. The 1747-BSN is strictly designed for the 1746 chassis backplane and is only compatible with SLC 500 processors (5/02 and higher).
Q: How many BSN pairs can I have in a single system?
A: A backup system can support up to eight 1747-BSN modules in each processor chassis, allowing you to back up multiple independent RIO or DH+ networks simultaneously.
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This backup scanner module provides essential system redundancy for critical applications using the primary 1747-SN Remote I/O scanner.
