GE IC687BEM731

Description

Product Description

The GE IC687BEM731 is a specialized high-speed serial communications module designed for the GE Fanuc Series 90-70 PLC system. This module serves as a critical gateway, enabling the PLC CPU to communicate with external devices such as operator interfaces (HMIs), bar code scanners, weighing systems, other PLCs, or supervisory computers using standard serial protocols. The primary function of the GE IC687BEM731 is to expand the communication capabilities of the Series 90-70 rack beyond the CPU’s built-in ports, providing additional configurable serial channels for data exchange and control. By implementing this module, system integrators can facilitate device networking, data logging, and remote monitoring, effectively integrating the PLC into a broader automation architecture. The GE IC687BEM731 is a key component for building interconnected and data-rich control systems in industrial environments.

Technical Parameters and Features

• Device Type: Serial Communications Module for Series 90-70 PLC.
• Compatibility: Designed for use in a Series 90-70 PLC rack (IC697 series). It occupies one slot in the rack and communicates via the VME backplane.
• Port Configuration: Typically provides two independent, configurable serial ports. Each port can be individually configured for different protocols and electrical standards.
• Supported Protocols: The module supports a range of common industrial serial protocols, which are selectable through configuration. These typically include:
  • SNP (Serial Network Protocol): GE’s proprietary protocol for communication with GE HMIs (Cimplicity, QuickPanel) and programming software.
  • Modbus RTU (Master/Slave): For interfacing with a vast array of third-party devices like drives, meters, and sensors.
  • ASCII (Full Duplex): For communicating with printers, scanners, and other character-based devices.
• Electrical Interfaces: The physical ports usually support both RS-232 (for point-to-point connections) and RS-422/485 (for multi-drop networks) standards, often via a single connector with configurable pin-outs.
• Configuration: Configured using the PLC programming software (Logicmaster 90 or later Proficy Machine Edition). Settings include baud rate, parity, stop bits, protocol selection, and data format.
• LED Indicators: Features status LEDs for power, port activity (Tx/Rx), and communication errors to aid in diagnostics.

Advantages and Key Features

• Enhanced Connectivity: The GE IC687BEM731 effectively doubles or provides dedicated serial communication paths for the PLC, freeing up the CPU’s programming port for development and allowing simultaneous data exchange with multiple external systems.
• Protocol Flexibility: The ability to configure each port for a different protocol (e.g., SNP for the HMI on Port 1, Modbus RTU Master for a sensor network on Port 2) makes the BEM731 module highly versatile for diverse application needs.
• Robust Industrial Design: As part of the rugged Series 90-70 family, it is built to withstand the temperature, vibration, and electrical noise typical of factory floors.
• Seamless Rack Integration: Being a VME bus module, it communicates with the CPU at high speed over the backplane, offering better performance and integration than an external serial gateway connected via I/O.
• Legacy System Lifeline: For the extensive installed base of Series 90-70 systems, modules like the IC687BEM731 are essential for maintaining, expanding, or interconnecting these reliable control systems without a full platform migration.

Application Case Studies in Various Fields

• Automated Packaging Line: A GE IC687BEM731 module in a 90-70 controller uses one port running SNP to communicate with a local GE QuickPanel HMI for operator control. The second port runs Modbus RTU Master to poll multiple weigh scales and inkjet printers for product tracking and labeling.
• Material Handling System: Used to create a peer-to-peer network between multiple PLCs controlling different conveyor sections. The modules are configured for SNP or a custom ASCII protocol to pass package routing and synchronization data.
• Water Treatment Plant: Interfaces with legacy flow meters and pump controllers that only support Modbus RTU. The BEM731 module acts as a Modbus Master, collecting data from these field devices for the PLC’s control algorithms.
• Factory Data Collection: One port is dedicated to a serial link with a plant-wide SCADA or MES system for production reporting, while the other port connects to a serial printer for local batch reports.

Comparison with Competing Products

Compared to using the CPU’s single serial port with a switch or using Ethernet-based communication modules, the GE IC687BEM731 offers specific benefits for serial-centric architectures:

1. Dedicated Hardware vs. Software Multiplexing: The IC687BEM731 provides dedicated hardware channels, ensuring consistent communication performance without being affected by the CPU’s program scan or the traffic on another port. Using a port splitter on the CPU port can lead to conflicts and slower response times.
2. Native Protocol Support vs. Custom Programming: The module has native, hardware-assisted support for key protocols like SNP and Modbus. Achieving the same functionality on a generic Ethernet module might require more complex socket programming in ladder logic.
3. Cost-Effective Serial Solution: For applications where existing devices use serial communication and an Ethernet overhaul is not justified, adding a BEM731 module is a cost-effective way to add connectivity compared to replacing multiple field devices or adding protocol converters.

Selection Advice and Important Notes

• Verify Rack and CPU Compatibility: Ensure your Series 90-70 CPU and rack firmware versions support the IC687BEM731 module. Consult the appropriate series compatibility guide.
• Plan Protocol and Port Assignment Carefully: Before configuration, clearly define which device connects to each port and which protocol it uses. Changing the protocol often requires re-configuration and download to the module.
• Use Correct Cabling and Termination: For RS-422/485 networks, use properly shielded, twisted-pair cable and install termination resistors at both ends of the network bus to prevent communication errors. Incorrect cabling is a primary cause of serial communication failure.
• Configure Communications in the CPU Logic: The module’s ports are controlled and data is exchanged through specific %AI/%AQ registers in the CPU’s memory map. The PLC program must include logic to read from and write to these registers to utilize the module effectively.
• Consider it a Legacy Solution: For new system designs, modern Ethernet-based communication (e.g., Genius, Profinet) is preferred. The GE IC687BEM731 should be selected primarily for expanding or maintaining existing Series 90-70 systems.

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