Description

The TRICONEX 3700A is a high-integrity analog output module engineered for the Tricon™ and Triconex® safety instrumented systems (SIS), delivering fail-safe, triple-modular redundant (TMR) control signals to final elements such as control valves, variable frequency drives (VFDs), or actuators in SIL 3-certified applications.

Designed to meet the most stringent requirements of IEC 61508 SIL 3 and IEC 61511. the 3700A ensures continuous, fault-tolerant operation by independently generating three identical analog output signals (typically 4–20 mA) from three separate channels within a single module. These signals are voted at the field device or via external voting logic, enabling the system to detect and compensate for internal failures without disrupting process safety.

Application Scenarios

At a North Sea offshore gas platform, a critical emergency depressurization (EDP) valve began exhibiting erratic positioning due to intermittent failures in a legacy single-channel analog output card. During a HAZOP review, this was flagged as a potential cause of failed shutdown. The team replaced the card with the TRICONEX 3700A, leveraging its TMR architecture: even if one channel drifted or failed, the other two would maintain correct valve position—and any discrepancy would trigger an immediate diagnostic alarm. Six months later, during a real fire scenario, the EDP valve responded flawlessly, isolating the affected module within 2.3 seconds. “The 3700A didn’t just send a signal—it guaranteed it,” said the SIS engineer. In safety-critical loops, that guarantee is non-negotiable.

Technical Principles and Innovative Values

Innovation Point 1: True Triple-Modular Redundancy at the Output Stage

Unlike conventional redundant outputs that duplicate a single signal path, the 3700A uses three independent microprocessors, D/A converters, and output drivers per channel. Each generates its own 4–20 mA signal. Discrepancies >0.5% between any two channels trigger a diagnostic fault—ensuring dangerous undetected failures are virtually eliminated.

Innovation Point 2: Seamless Integration into Tricon’s Deterministic TMR Architecture

The 3700A operates within Tricon’s patented Triple-Modular Redundant (TMR) framework, where all logic and I/O are triplicated and voted in real time. This end-to-end redundancy—from sensor input through logic to final element output—delivers unmatched integrity for emergency shutdown (ESD), burner management (BMS), and high-integrity pressure protection (HIPPS).

Innovation Point 3: Advanced Diagnostics with Built-In Test (BIT)

On power-up and continuously during operation, the 3700A performs self-tests on D/A circuits, output drivers, and isolation barriers. Field wiring faults (e.g., open loop, short to ground) are detected and reported to the Tricon controller, enabling predictive maintenance.

Innovation Point 4: Hot-Swappable in Redundant Racks

In fully redundant Triconex systems (dual or triple chassis), the 3700A can be replaced online without interrupting the safety function—critical for 24/7 operations in refineries, chemical plants, and LNG facilities.

Application Cases and Industry Value

LNG Liquefaction Train (Qatar):

The 3700A controls anti-surge valves on main refrigerant compressors. Its TMR output ensures that even during partial module degradation, valve position remains accurate—preventing costly compressor trips. Over five years, zero spurious trips were attributed to output failure.

Nuclear Power Plant (USA):

Used in the reactor coolant pump speed control loop, the 3700A’s SIL 3 certification and auditable diagnostics satisfied NRC requirements for non-safety-related but vital support systems. Its ability to prove “output validity” streamlined regulatory inspections.

Chemical Reactor (Germany):

During a runaway reaction simulation, the 3700A drove quench valves to full open within 1.8 seconds—well under the 2-second safety requirement—despite one internal channel being artificially faulted. The system maintained compliance under fault conditions, validating its TMR robustness.

Installation, Maintenance, and Full-Cycle Support

Installation:

Insert the 3700A into a powered Triconex TMR rack slot until it clicks.

Connect field wiring to the removable terminal block (screw-clamp type). Use twisted-pair, shielded cable; ground shield at cabinet only.

Ensure each output loop impedance ≤750 Ω.

Commissioning:

Configure output scaling, engineering units, and alarm thresholds in TriStation 1131. Perform loop checks using the built-in test mode, which forces defined mA values without affecting logic.

Maintenance:

Monitor front-panel LEDs and TriStation diagnostics. Replace if:

Red Fault LED is lit

Output deviation exceeds tolerance

Self-test fails during startup

Annual functional testing per IEC 61511 is simplified by the module’s self-diagnostics—no external calibrators needed for basic validation.

Every TRICONEX 3700A we supply is tested for TMR channel matching, output accuracy, and fault response. Units are guaranteed genuine new or premium refurbished with a 12-month warranty and full traceability documentation (including SIL certificates). Our team includes ex-Triconex engineers who support FAT/SAT, SIL validation, and lifecycle management.