1785-BEM |Allen Bradley | PLC-5 Backup Communications Expansion Module

Product Overview

The Allen Bradley 1785-BEM functions as a dedicated Backup Communications Expansion Module for the PLC-5 platform. It provides the essential hardware layer for high-availability control systems by managing redundant communication paths between processors. This module ensures that your automation network remains operational even if a primary communication link fails. We supply this unit as 100% Brand New, delivering a factory-fresh solution for legacy system upgrades and critical spares inventory.

Technical Specifications

The 1785-BEM integrates seamlessly into the 1771 universal I/O chassis, drawing minimal power from the backplane.

Engineering Advantages

• Redundancy Management: The 1785-BEM enables the secondary processor in a "Hot Backup" configuration to synchronize its communication status with the primary controller. This synchronization allows for a near-bumpless transfer of control during hardware or network failures.

• Low Thermal Impact: Drawing only 0.6 Amps at 5 VDC, the module generates negligible heat. This efficiency allows you to mount it in high-density 1771 chassis without compromising the thermal window of adjacent analog or specialty modules.

• Seamless Backplane Integration: The module utilizes the standard 1771 slot architecture. It requires no external power wiring, as it pulls all necessary operating voltage directly from the chassis power supply, simplifying cable management in cramped enclosures.

• Critical Link Restoration: By expanding the communication capabilities of the PLC-5 processor, the 1785-BEM provides a fail-safe mechanism for Remote I/O and DH+ (Data Highway Plus) links, preventing total system shutdowns in continuous process industries like oil and gas or water treatment.

FAQs

• When does a system require the 1785-BEM module?

  You must install the 1785-BEM whenever you configure a PLC-5 system for redundant "Hot Backup" operation. It handles the specific communication exchange required to keep the standby processor's data tables updated with the primary processor's live values.

• Can I install the 1785-BEM in any slot?

  Typically, you install the 1785-BEM in a slot immediately adjacent to the PLC-5 processor or in a designated slot defined by your redundancy hardware setup (such as a 1785-BCM backup module). Always refer to your specific redundancy firmware requirements for slot assignment.

• Is this module compatible with all PLC-5 processors?

  The 1785-BEM supports standard PLC-5 processors that utilize the 1771 universal I/O chassis. However, verify that your processor firmware supports backup expansion functions before commissioning.

• Does this brand new unit require any special configuration?

  As a 100% Brand New original unit, it arrives with factory-default settings. Configuration primarily occurs within the RSLogix 5 software environment and via the physical switch settings on the primary redundancy hardware (1785-BCM) that this expansion module supports.