Allen‑Bradley 1785‑BEM/B PLC‑5 Backplane Expansion Module

Product Overview

The Allen‑Bradley 1785‑BEM/B is a backplane expansion module for Rockwell PLC‑5 programmable controller systems. Installed in a PLC‑5 chassis slot, it provides the hardware interface to connect additional expansion I/O racks via 1785‑CBK expansion cable. This module extends local backplane I/O capacity without consuming controller communication ports, supporting multi‑chassis local I/O layout for legacy PLC‑5 automation systems. Original production is discontinued, mainly supplied as surplus and refurbished spare parts for existing system maintenance and retrofit.

Series

PLC‑5 Control System Series. The PLC‑5 platform includes CPU processors, power supplies, I/O modules, backplane expansion accessories and communication adapters, widely deployed in heavy‑industry discrete and process automation applications.

Product Features

Local backplane expansion interface for PLC‑5 chassis
Connect secondary expansion racks with 1785‑CBK expansion cable
Supports multi‑rack local I/O expansion architecture
Draws power from PLC‑5 chassis 5 VDC backplane, no external power required
Standard single‑slot chassis form factor for PLC‑5 rack installation
Status LED indicator for module health and expansion link diagnosis
Revision B hardware variant with improved circuit stability
Simple drop‑in slot installation, no complex configuration required
Works with full range of PLC‑5 digital and analog I/O modules

Product Parameters

表格

Item	Value
Part Number	1785‑BEM/B
Module Type	Backplane Expansion Module
Hardware Revision	B
Chassis Requirement	PLC‑5 series chassis (1771 series racks)
Expansion Cable	1785‑CBK cable (required)
Backplane Power Consumption	0.8 A @ 5 VDC
Slot Occupancy	1 single chassis slot
Indicator	Module status LED
Operating Temperature	0 °C ~ +60 °C
Storage Temperature	‑40 °C ~ +85 °C
Humidity	5‑95 % non‑condensing
Weight	0.23 kg
Certifications	UL, CSA, CE

Product Specifications

Mechanical: 1771‑style single‑slot Eurocard for PLC‑5 chassis
Compatibility: Matches all PLC‑5 CPUs and 1771 I/O racks; cannot be used with ControlLogix or SLC‑500 systems
Cable limitation: Follow Rockwell official length limits for 1785‑CBK expansion cable
Lifecycle: Original manufacturing discontinued; available as surplus / refurbished spare‑part units
Installation note: Must be seated properly in chassis slot; power off rack before module replacement

Function

Provide physical backplane expansion signal interface for PLC‑5 main chassis
Transmit backplane bus signals to secondary I/O racks over 1785‑CBK cable
Expand total local I/O quantity of PLC‑5 controller system
Realize multi‑chassis local rack layout without consuming communication channels
Indicate operating status via onboard LED for on‑site troubleshooting

Purpose

Expand local I/O rack capacity of PLC‑5 control systems; enable multi‑chassis hardware layout; serve as critical spare‑part for legacy PLC‑5 automation cabinet repair, maintenance and retrofit projects.