Description
The Triconex 3721 is a high-reliability, Triple Modular Redundant (TMR) Analog Input Module designed by Schneider Electric (Invensys) for Tricon v10.2 and later Safety Instrumented Systems (SIS).
It features 32 differential, DC-coupled channels and is engineered for critical safety functions such as Emergency Shutdown (ESD), Burner Management Systems (BMS), and Fire and Gas (F&G) monitoring.
Key Technical Specifications
| Parameter | Specification Details |
| Module Type | TMR Analog Input (AI), Differential, DC-Coupled |
| Channel Count | 32 independent differential channels |
| Input Voltage Range | 0 to 5 VDC (unipolar) or –5 to +5 VDC (bipolar), +6% over-range |
| Current Loop Support | 0 to 20 mA (via external 250 Ω precision shunt resistor) |
| Programmable Resolution | 12-bit or 14-bit (configured in TriStation 1131) |
| Input Update Rate | ~10 ms (typical for all channels) |
| System Accuracy | < 0.15% of Full Scale Range (FSR) from 0°C to 60°C |
| Common Mode Rejection | -85 dB (DC to 100 Hz) typical |
| Overvoltage Protection | 150 VDC continuous / 115 VAC continuous |
| Logic Power Consumption | < 15 Watts |
| Safety Compliance | SIL 3 Capable (IEC 61508) |
TRICONEX 3721
TRICONEX 3721
TRICONEX 3721
Core Functional Features
- Mid-Value Selection Algorithm: The module contains three completely independent input channels (legs). Each leg measures the field signal, converts it to a digital value, and passes it to the main processors. A mid-value selection algorithm selects the correct value for each scan to ensure unmatched fault tolerance.
- Comprehensive Self-Diagnostics: Continuous background testing monitors channel health. A channel diagnostic failure activates the front-panel FAULT indicator and generates a chassis alarm without interrupting normal operations, as the module can safely function with up to two channel failures.
- On-Line Hot Replaceable: Supports hot-standby mode, allowing maintenance teams to swap out a faulty module online under approved safety protocols without shutting down the system.
- Color Code & Identification: Features a Yellow color band on the front panel for quick identification in the I/O chassis and is built with mechanical positioning keys to ensure correct installation.
Installation & System Compatibility
- Chassis Integration: Designed strictly for Tricon high-density or upgraded low-density chassis running system firmware v10.2.x or later.
- Field Termination: Requires separate External Termination Panels (ETP/FTA) and dedicated interface cables to bridge field wiring to the backplane. It is highly recommended to use twisted, shielded pairs for low-level analog routing and ground the shields at a single termination point to prevent ground loops.
