TRICONEX

Product Overview

AI3351S2 is a dedicated analog input card for Schneider Triconex TMR triple modular redundant SIS safety instrumented systems. The suffix S2 stands for the updated hardware revision. It collects standard 4–20mA analog field process signals and provides underlying process data for safety interlocks such as ESD, BMS and unit protection, complying with IEC61508 SIL3 functional safety standards.

1. Collection and conversion of field 4–20mA analog process signals It receives 4–20mA current signals transmitted from field transmitters, including process measurements of pressure, temperature, liquid level, flow rate and oxygen content. High-precision analog-to-digital conversion circuits convert analog current signals into digital data, which are transmitted to the MP3009X main processor for safety logic calculation.
2. Triple Modular Redundant (TMR) fault-tolerant hardware architecture The module is equipped with three fully independent acquisition circuits that sample the same transmitter signal synchronously and compare three groups of sampled values via real-time hardware with 2-out-of-3 voting logic. If one channel suffers open circuit, short circuit or hardware failure, the other two channels maintain normal sampling without signal distortion, false alarms or spurious interlock actions.
3. Full-time online fault diagnosis for input loops It continuously monitors the status of each input loop, automatically detecting faults such as broken transmitters, short circuits, abnormal loop impedance, out-of-range signals (below 4mA or above 20mA) and loose wiring. It generates fault alarms and millisecond-level Sequence of Events (SOE) logs uploaded to HMI operator stations and engineering workstations for fast troubleshooting of instruments and field cables.
4. Electrical isolation and anti-interference protection Built-in opto-isolation circuits isolate ground loops and common-mode electromagnetic interference between the main control rack and field transmitters, suppress surges, harmonics and interference from variable frequency equipment, and protect the CPU host and precise sampling circuits of the module, suitable for high-interference hazardous industrial sites including chemical, oil & gas and power plants.
5. Fail-safe logic processing In case of severe mismatch among three sampling channels, communication loss or module hardware failure, the system automatically identifies the fault and marks the channel as faulty to trigger safety alarms, while keeping signal acquisition of other healthy channels intact, preventing failure of the whole safety interlock caused by a single measurement point fault.
6. High-precision stable sampling for precise safety processes Adopting sampling circuits with excellent linearity and low temperature drift, the module delivers high signal acquisition accuracy to capture tiny process fluctuations accurately, ensuring reliable judgment of delicate safety interlocks such as overpressure, overtemperature and low liquid level protection.
7. Support online hot-swap maintenance on rack The AI3351S2 module can be replaced individually while the system operates under full load. Other analog input channels remain unaffected during replacement, and the entire SIS safety interlock system runs continuously without full plant shutdown for maintenance.
8. Multi-channel centralized acquisition to simplify field wiring Each card integrates multiple independent isolated acquisition channels to connect multiple field transmitters simultaneously. Matched factory pre-terminated cables and terminal block modules realize centralized cable distribution and reduce wiring complexity inside control cabinets.