Description

The Foxboro RH931RQ is a high-reliability, 32-channel digital input module designed for use within the Foxboro I/A Series® Distributed Control System (DCS)—a flagship automation platform widely deployed in power generation, oil & gas, chemical processing, and water treatment facilities. As part of the Remote I/O (RIO) architecture, the RH931RQ enables decentralized signal acquisition from field devices such as limit switches, pressure alarms, motor starters, and safety interlocks, transmitting data back to central controllers over redundant fiber-optic or copper communication links.

Engineered for mission-critical applications, the Foxboro RH931RQ supports a broad input voltage range (24 VDC to 125 VAC/VDC), allowing direct connection to both modern low-voltage sensors and legacy high-voltage plant signals—eliminating the need for external relays or signal conditioners. Each channel features optical isolation and transient suppression, ensuring immunity to ground loops, EMI, and lightning-induced surges common in industrial environments. The RH931RQ mounts on standard DIN rails within ruggedized I/O cabinets and integrates seamlessly with Foxboro’s Fieldbus Modules (FBMs) and Workbench Station (FWS) engineering tools for configuration, diagnostics, and alarm management.

Technical Specifications

Main Features and Advantages

Wide input compatibility for hybrid plants:
The Foxboro RH931RQ uniquely bridges legacy and modern instrumentation by accepting both 24 VDC (standard for new sensors) and up to 125 VAC/VDC (common in older turbine trip circuits or boiler protection systems). This eliminates costly field rewiring during DCS upgrades—critical in brownfield sites where replacing every switch or relay is impractical. Input filtering and hysteresis prevent chatter from noisy contacts, ensuring stable logic interpretation.

Robust isolation and surge protection:
Each of the 32 channels on the RH931RQ is individually optically isolated from the system backplane, breaking ground potential differences that could otherwise damage controllers. Built-in metal-oxide varistors (MOVs) and TVS diodes clamp transients exceeding ±2 kV (per IEC 61000-4-5), making the RH931RQ suitable for outdoor substations or coastal refineries exposed to lightning.

Seamless DCS integration with full diagnostics:
When installed in an I/A Series cabinet, the RH931RQ appears automatically in the Foxboro Workbench configuration tool. Engineers can monitor real-time input states, configure alarm deadbands, and trace signal paths without third-party software. Failed modules trigger system-wide alerts, and hot-swap capability (in supported chassis) allows replacement without shutting down the entire I/O rack—minimizing process downtime.

Scalable remote architecture:
As part of the Remote I/O strategy, the RH931RQ can be located hundreds of meters from the main controller—ideal for sprawling facilities like LNG terminals or combined-cycle plants. Communication over fiber optics ensures noise immunity and electrical separation between buildings. Multiple RH931RQ units can populate a single RIO node, enabling high-density signal concentration near field equipment.

Application Field

In fossil fuel power plants, the Foxboro RH931RQ is commonly used to monitor boiler flame failure detectors, turbine overspeed trips, and generator breaker status—signals often sourced at 125 VDC from battery-backed DC systems. Its ability to directly interface with these high-voltage circuits avoids intermediate relay panels, improving reliability and reducing maintenance.

Within offshore oil platforms, the RH931RQ aggregates emergency shutdown (ESD) signals from fire/gas detectors, valve position limits, and pump vibration switches. Its rugged design and compliance with hazardous area standards (when installed in appropriate enclosures) make it suitable for Zone 2 environments. Similarly, in chemical batch reactors, the RH931RQ captures lid closure interlocks and high-level alarms—feeding critical data into safety instrumented functions (SIFs) managed by the I/A Series logic solvers.

Even in municipal water treatment, aging SCADA systems are being modernized by replacing discrete PLC racks with Foxboro RH931RQ modules connected to a centralized I/A Series DCS—enabling unified operator visibility, historical trending, and cybersecurity hardening under a single architecture.

Related Products

• RH932RQ: 32-channel digital output counterpart to the RH931RQ

• FBM207: Older Foxboro FBM module with 16 digital inputs; RH931RQ offers higher density

• RH911: Analog input RIO module (8-channel, 4–20 mA) for mixed-signal applications

• I/A Series CP60 or CP70: Central processing units compatible with RH931RQ RIO nodes

• FBM242: High-speed digital input FBM; used when sub-millisecond response is required

• RH991: Remote I/O communications interface module (fiber/copper gateway)

• Schneider Electric EcoStruxure™ Foxboro DCS: Modern evolution of the I/A Series platform

Installation and Maintenance

Pre-installation: Verify that the target I/A Series RIO node supports the RH931RQ (firmware ≥ v4.2 recommended). Ensure field wiring uses twisted-pair, shielded cable with shield grounded at the cabinet end only. Confirm input source voltages match the configured range (AC vs. DC)—miswiring can damage channels. Power must be redundant if used in safety-critical loops.

Maintenance: Use Foxboro Workbench to periodically check for “sticky” inputs or intermittent faults. Inspect front-panel LEDs: green = powered and communicating; red = fault (e.g., loss of comms or internal error). Avoid opening the module—no user-serviceable parts inside. Replace units showing repeated CRC errors or unresponsive channels. Store spares in dry, static-safe conditions; expected service life exceeds 15 years under normal conditions.