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FOXBORO FBM242
FOXBORO FBM242
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Foxboro RH926GH | Compression Screw Termination Assembly – Technical Brief

  • Model: RH926GH (supersedes P0926GH)
  • Alt. P/N: P0926GH (older version)
  • Product Series: Foxboro I/A Series Fieldbus Modules
  • Hardware Type: Compression Screw Termination Assembly (TA) for FBM231
  • Key Feature: Field wiring termination for RS-232/422/485 serial communication interfaces
  • Primary Field Use: Provides connection point between FBM231 module and external serial devices/modems in multi-protocol communication applications.
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Part number: Foxboro RH926GH
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Description

Hard-Numbers: Technical Specifications

  • Series: I/A Series Fieldbus
  • Module Compatibility: FBM231 Field Device System Integrator Module (Four Serial Ports, Redundant)
  • Termination Type: Compression Screw
  • Supported Interfaces:
    • RS-232 (DB-25 cable to modem/converter): Up to 15 m (50 ft)
    • RS-422: Up to 1200 m (3937 ft)
    • RS-485: Up to 1200 m (3937 ft)
  • Transmission Rates: 300, 600, 1200, 2400, 4800, 9600, 19200, 38400, 57600 baud
  • Termination Cable Type: Type 5 (LSZH cable jacket)
  • Available Cable Lengths:
    • 1.0 m (3.2 ft): RH928AW (supersedes P0928AW)
    • 2.0 m (6.6 ft): RH928AX (supersedes P0928AX)
    • 3.0 m (9.8 ft): RH928AY (supersedes P0928AY)
    • 5.0 m (16.4 ft): RH928AZ (supersedes P0928AZ)
  • Dimensions:
    • Height: 111 mm (4.37 in)
    • Width: 80 mm (3.13 in)
    • Depth: 72 mm (2.83 in)
    • Mounting Hole Centers: 216 mm (8.51 in)
  • Weight: 272 g (0.6 lb) approximate
  • Cable Temperature Range: -40 to +105°C (-40 to +221°F) (LSZH jacket)
  • Cable Material: Low Smoke Zero Halogen (LSZH) thermoplastic or thermoset compounds
FOXBORO FBM242

FOXBORO FBM242

The Real-World Problem It Solves

Serial communication with field devices, PLCs, and third-party equipment often requires organized, secure field wiring terminations. Loose connections, improper grounding, and cable management issues cause intermittent communication failures in industrial environments. The RH926GH termination assembly provides a standardized, compression screw termination point that ensures reliable wire connections for RS-232/422/485 interfaces, supports long-distance communication (up to 1200 m for RS-422/485), and uses LSZH cable material for safety in hazardous or enclosed environments.
Where you’ll typically find it:
  • Multi-protocol gateway installations connecting Foxboro DCS to Modbus/Profibus networks
  • Remote terminal unit (RTU) connections via serial links
  • Smart instrument integration through serial communication interfaces
  • Legacy equipment migration projects requiring RS-232/422/485 connectivity
  • Third-party controller and PLC communication links
Bottom line: It provides reliable, standardized field wiring termination for FBM231 serial communication interfaces with support for multiple protocols and long-distance cabling.

Hardware Architecture & Under-the-Hood Logic

This termination assembly serves as the field wiring interface between the FBM231 module and external serial communication devices. It uses compression screw terminals for secure wire connections and provides termination points for RS-232, RS-422, and RS-485 interfaces.
  1. The FBM231 module connects to the RH926GH termination assembly via Type 5 LSZH cable (lengths: 1-5 meters).
  2. Field devices or modems connect to the termination assembly through designated terminal points for each protocol.
  3. RS-232 connections use DB-25 cables (up to 15 m) connecting to customer-supplied devices or modems.
  4. RS-422 and RS-485 connections support longer distances (up to 1200 m) using 4-wire physical media.
  5. Compression screw terminals provide secure, vibration-resistant wire connections for all signal lines.
  6. The assembly isolates field wiring from the module, allowing for hot-swappable maintenance without disrupting system operation.
  7. LSZH cable jacket material ensures limited smoke and halogen emissions during fire exposure, meeting safety requirements for enclosed environments.
  8. Multiple baud rates (300-57600) are supported to accommodate various device communication requirements.
  9. The assembly mounts on Modular Baseplate alongside FBM231, providing organized cable management in enclosures.
FOXBORO FBM242

FOXBORO FBM242

Field Service Pitfalls: What Rookies Get Wrong

Incorrect Cable Length SelectionRookies select the wrong termination cable length between FBM231 and RH926GH, causing installation issues or excessive cable slack. The assembly only supports specific cable lengths (1.0, 2.0, 3.0, or 5.0 meters).
  • Field Rule: Verify the required distance between the module and termination assembly before installation. Use only the specified cable lengths (RH928AW/AX/AY/AZ) to ensure proper fit and cable management in the enclosure.
Mixing RS-232 and RS-422/485 WiringTechnicians incorrectly wire RS-232 devices to RS-422/485 terminals or vice versa. This causes communication failures because the physical layer requirements differ significantly (point-to-point vs. multi-drop).
  • Quick Fix: Identify the communication protocol required by the connected device before wiring. RS-232 uses DB-25 connectors for point-to-point links up to 15 meters. RS-422/485 use terminal block connections supporting longer distances and multi-drop configurations. Verify device documentation for correct interface type.
Exceeding Maximum Cable DistanceNew engineers deploy RS-422/485 cabling beyond the 1200-meter limit, assuming Ethernet-like distance capabilities. Signal degradation and communication timeouts occur beyond the specified maximum.
  • Field Rule: For RS-422/485 connections, ensure total cable length does not exceed 1200 meters (3937 feet). If longer distances are required, install repeaters or optical converters. For RS-232, never exceed 15 meters between termination assembly and connected device.
Poor Compression Screw TerminationInstallers don’t properly strip wire length or over-tighten compression screws, causing weak connections or broken strands. Loose terminals result in intermittent communication failures that are difficult to diagnose.
  • Field Rule: Strip wire insulation according to the termination assembly specifications (typically 6-8 mm). Insert fully into the compression terminal and tighten screw to manufacturer-specified torque. Do not over-tighten, which can damage terminal hardware. Perform a pull-test to verify secure connection.
Ignoring LSZH Cable Requirements in Hazardous AreasRookies replace LSZH (Low Smoke Zero Halogen) termination cables with standard PVC jacketed cable in hazardous or enclosed environments. During fire conditions, non-LSZH cables emit toxic smoke and halogens, violating safety standards.
  • Quick Fix: Always use the specified Type 5 LSZH cables (RH928 series) for connections between FBM231 and RH926GH in hazardous or confined spaces. LSZH material emits limited smoke and no halogens when exposed to fire, meeting IEC safety requirements for enclosed industrial environments.
Please note: The listed price is for reference only and is not binding. Final pricing and terms are subject to negotiation based on current market conditions and availability.

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