Tricon 3664 and 3674 are key components of the Tricon Safety System under Invensys (now Schneider Electric). They usually appear in pairs as digital output modules (DO modules) and matching terminal boards/substrates.
The following is a detailed technical analysis of these two models:

1. Product positioning and relationship
TRICONEX 3664: This is the core Digital Output Module. It is responsible for executing output instructions after logical operations and driving field devices.
TRICONEX 3674: This is a terminal board or base used in conjunction with the 3664 module. It provides on-site wiring terminals to introduce and connect on-site signals (such as solenoid valves, relay power supplies) to the 3664 module, while also providing signal isolation and distribution functions.
Note: In some contexts, users may refer to «3664/3674» as a whole system component, namely «digital output channel with terminal board».

2. Main technical characteristics
Triple Modular Redundancy (TMR) Architecture
Both components serve the core of the Tricon system — TMR (Triple Modular Redundancy) architecture.
The 3664 module contains three independent output channels internally. The system will use a voting mechanism of «choose one out of two» or «choose two out of three» for the data of these three channels. If one of the channels fails, the system will automatically block that channel and allow the other two normal channels to continue working, ensuring that a single point of failure will not cause the system to shut down or malfunction.
Functional purpose
Application scenarios: Mainly used for emergency shutdown systems (ESD), fire and gas systems (F&G), and critical process interlocking.
Control object: Used to drive high reliability on-site actuators, such as:
Emergency shut-off valve (SOV)
relay coil
indicator light
Other 24V DC loads that require high safety control.
Electrical specifications (typical values)
Working voltage: usually 24V DC (please refer to the hardware manual for details, some versions may support different voltage ranges, but 24V is the most common).
Output type: dry contact or power output, with short-circuit protection and open circuit detection functions.
Diagnostic capability: The module has powerful self diagnostic capabilities, which can monitor output status, power health, and communication integrity in real time, and report faults through system software.

3. System advantages
High availability: allows online maintenance and module replacement (if the system configuration supports hot swapping) without stopping the production process.
High Safety Integrity: Compliant with SIL 3 (IEC 61508/61511) safety level requirements, it is the preferred safety controller component for the petrochemical, power, and oil and gas industries.
Fault tolerance: Even in the event of hardware failure, power fluctuations, or external interference, the system can still maintain a safe state or continue to operate.
4. Common application industries
Oil and gas extraction and refining
Chemical production equipment
Power plant (turbine control)
Pipeline transportation system