Description
Product Overview
1785-BEM is an Allen‑Bradley (Rockwell Automation) backplane expansion module designed for the legacy PLC‑5 programmable controller system. Installed in a slot of the primary PLC‑5 chassis, it provides the hardware interface to connect remote expansion I/O racks via the 1785‑CBK expansion cable. It extends local backplane I/O capacity without consuming the processor’s communication ports, supporting multi-chassis local I/O layouts for older PLC‑5 automation systems. Rockwell has discontinued original production; available units are new surplus or fully tested refurbished spare parts for maintenance and retrofit of existing plants.
Technical Specifications
| Item | Parameter |
|---|---|
| Manufacturer | Allen‑Bradley (Rockwell Automation) |
| Part Number | 1785-BEM |
| Product Type | Backplane Expansion Module |
| Compatible Platform | PLC‑5 controller, 1771 I/O chassis |
| Required Cable | 1785‑CBK expansion cable |
| Backplane Current Draw | 0.8 A @ 5 VDC |
| Chassis Slot Occupancy | 1 single slot |
| Operating Temperature | 0 °C ~ +60 °C |
| Storage Temperature | -40 °C ~ +85 °C |
| Humidity | 5%–95% RH, non-condensing |
| Vibration Resistance | 2 g, 10–500 Hz |
| Shock Resistance | 30 g operating, 50 g non-operating |
| Net Weight | Approx.0.23 kg |
| Enclosure Rating | IP20 (board assembly, chassis mounted) |
Key Features
- Local Backplane Expansion Interface: Enables the main PLC‑5 rack to link additional 1771 I/O expansion racks over dedicated expansion cable, expanding total I/O points.
- No Processor Communication Port Consumption: Expansion traffic runs over dedicated backplane link instead of PLC communication ports, leaving DH+ or other network ports free.
- Simple Plug-in Installation: Fits into any free slot on the primary PLC‑5 chassis, no complex configuration software required for basic rack extension.
- Status LED Indication: Onboard LEDs show module health, link status and cable fault alarms for quick troubleshooting.
- High Noise Immunity: Optimized for industrial control cabinet environments with electrical noise and vibration.
- Legacy System Spare: Original manufacturing stopped by Rockwell; only surplus / refurbished stock for existing PLC‑5 system repairs.
Applications
- Petrochemical plant legacy PLC‑5 control systems
- Power station auxiliary control panels with PLC‑5 controllers
- Water treatment factory older automation racks
- Material handling, metal processing machinery retrofits
- Any existing 1771 I/O chassis expansion for PLC‑5
Installation & Maintenance Notes
- Execute lockout-tagout before removing or inserting the module.
- Apply ESD protection during handling to prevent PCB damage.
- Use genuine 1785-CBK cable; avoid over-length or damaged expansion cables, which will trigger link faults.
- Keep expansion cable separated from high-current power cables to reduce EMI interference.
- Check LED status after power-up to verify rack communication.
- Confirm full part number match when replacing spare module and validate all expansion rack addressing.
- Inspect connector pins for bending or corrosion during scheduled cabinet overhaul.
FAQ
Q: What cable works with the 1785-BEM? A: The dedicated 1785-CBK expansion cable connects 1785-BEM to the expansion chassis.
Q: What is the difference between 1785-BEM and 1785-BCM? A: 1785-BEM = backplane expansion module for adding local I/O racks. 1785-BCM = backup communication module for redundant PLC‑5 processor communication.
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