Triconex Tricon Analog Input Modules: AI3351 S2

Technical Dossier

Product Details And Specifications

Triconex Tricon Series Technical Notes

The Triconex Tricon platform is a Triple Modular Redundant (TMR) Safety Instrumented System (SIS) deployed across the most demanding process industries globally — including petrochemical complexes, LNG terminals, nuclear power stations, offshore platforms, and refinery critical-path units. Developed by Triconex (now a brand under Schneider Electric), the Tricon architecture achieves IEC 61511 SIL 3 certification by executing three independent processing paths simultaneously and voting on outputs via a 2-out-of-3 (2oo3) logic scheme. This design eliminates single points of failure and sustains safe operation even under partial hardware degradation. The AI3351 S2 is a field-proven Analog Input module within this ecosystem, designed to interface with 4–20 mA transmitters and process up to 16 channels of analog signal with per-channel diagnostics. Its deployment spans safety-critical loops including pressure, temperature, flow, and level measurement in SIL 2/3 rated applications.

The Evolution of Tricon Architecture

The Tricon platform was introduced in the late 1980s as a successor to earlier relay-based and single-channel SIS architectures. The original Tricon v1 chassis established the TMR backplane bus standard that remains backward-compatible through subsequent hardware generations. The v9 and v10 chassis generations introduced enhanced I/O density and improved diagnostics. The v11 generation (Tricon CX) transitioned to a more compact form factor with integrated communication capabilities and support for TriStation 1131 v4+ programming environments.

Key compatibility considerations: Tricon I/O modules are chassis-slot specific — AI modules such as the AI3351 S2 are compatible with the standard Tricon main chassis (3006, 3007, 3008 series) but require correct slot addressing in the TriStation configuration. Modules from the v9/v10 era are generally interchangeable within the same chassis generation. Migration from v9 to Tricon CX requires hardware replacement and TriStation project re-validation. Many facilities operating pre-2010 Tricon installations continue to source legacy modules for life extension programs rather than undertaking full system replacement, given the cost and re-validation burden associated with SIL-rated system upgrades.

Tricon Full Catalog & Functionalities (SKU List)

Analog Input Modules (AI)

• AI3351 S2: 16-channel 4–20 mA analog input, TMR, SIL 3 rated, per-channel HART support
• AI3351: 16-channel analog input module, earlier revision without S2 enhanced diagnostics
• AI3310: 8-channel analog input, 4–20 mA, TMR architecture, legacy v9 chassis compatible
• AI3311: 8-channel analog input with enhanced signal conditioning, v10 chassis
• AI4001: 32-channel analog input, high-density, Tricon CX platform

Analog Output Modules (AO)

• AO3481: 8-channel 4–20 mA analog output, TMR, SIL 2 rated, loop-powered
• AO3485: 8-channel analog output with enhanced current sourcing, v10/v11 compatible

Digital Input Modules (DI)

• DI3301: 32-channel 24 VDC digital input, TMR, field-proven in ESD applications
• DI3302: 32-channel 120 VAC digital input, TMR, for legacy AC field wiring
• DI3303: 32-channel 48 VDC digital input, TMR
• DI3304: 32-channel digital input, 24 VDC, enhanced noise immunity, v10 chassis
• DI3305: 32-channel digital input, 24 VDC, Tricon CX compatible

Digital Output Modules (DO)

• DO3401: 16-channel 24 VDC digital output, TMR, solid-state relay, SIL 3
• DO3481: 8-channel relay output, TMR, for high-current field devices
• DO3485: 16-channel digital output, 24 VDC, enhanced diagnostics, v10/v11

CPU & Main Processor Modules

• 3008: Tricon Main Chassis, 8-slot, standard TMR backplane
• 3007: Tricon Main Chassis, 7-slot variant
• 3006: Tricon Main Chassis, 6-slot, legacy installations
• 3700A: Tricon TMR Main Processor, v9 generation, 32-bit architecture
• 3701: Tricon TMR Main Processor, v10 generation, enhanced scan rate
• 3703E: Tricon Enhanced Main Processor, Ethernet-capable, v10/v11

Communication & Network Modules

• 4351B: Tricon Communication Module (TCM), Modbus TCP / EtherNet/IP gateway
• 4119A: Tricon Hiway Interface Module, for DCS integration via proprietary Triconex Hiway
• 4100: Tricon Network Communication Module, legacy RS-485 Modbus RTU

Power Supply Modules

• 8312: Tricon Power Supply Module, 24 VDC input, redundant pair configuration
• 8110: Tricon AC Power Supply, 120/240 VAC input, chassis-mount

Sourcing Hard-to-Find & Obsolete Tricon Parts

A significant portion of the global Tricon installed base operates on v9 and v10 hardware that Schneider Electric has transitioned to end-of-active-support status. For facilities under long-term service agreements or operating under regulatory frameworks that prohibit unplanned system replacement (nuclear, offshore, chemical), sourcing certified spare modules is the primary lifecycle extension strategy.

Quality Control for the Tricon Range

Tricon modules present specific test challenges due to their TMR backplane architecture. Standard bench power-up is insufficient — modules must be tested within a functional Tricon chassis to validate all three processing legs independently. DriveKNMS employs the following test protocol for Tricon I/O modules:

• Chassis-level power-on test: Module inserted into a live Tricon test chassis; TriStation 1131 diagnostics polled for fault flags on all three legs (Leg A, B, C).
• Analog signal injection (AI modules): Calibrated 4–20 mA source applied to each channel; output values verified against expected engineering unit conversion within ±0.1% of span.
• HART communication verification (AI3351 S2): HART master polling confirms device descriptor and PV readback on HART-enabled channels.
• Backplane bus integrity check: TMR voter logic verified by inducing single-leg signal deviation and confirming 2oo3 voting output remains correct.
• Thermal soak: Modules operated at elevated ambient (50°C) for minimum 4 hours to screen latent component failures.
• Final inspection: Connector pins, PCB, and conformal coating inspected under magnification; firmware revision recorded.