Triple modular redundant architecture

To avoid failure of input acquisition and of the voter, TMR (triple modular redundancy) architecture triples the entire chain as shown in Figure 1.30. 

B) typical 2oo3 architectural block diagram, and (C) triple modular redundancy (Typical). 

Invensys-Schneider Tricon uses triple modular redundant (TMR) architecture in which three parallel control paths are integrated into a single overall system. This gives high fault tolerance, with no process-controlled interrupts and extensive self-test and diagnostics. 

Another option might have been the implementation of a triple modular redundant [4] (TMR, fault masking structural redundancy) system with robust majority voting schemes at the actuators. Such systems can be built either with synchronously running processor units and distributed local code/data memories, or asynchronously running processor units with local access to code and shared access to triple redundant data memories. The complexity and hardware demand of such a system architecture is so high, however, that this idea had to be rejected for technical reasons (mass, volume, harness, power consumption, etc.). 

The safety systems built on the loo2D modules have found a strong market in the general area of process plant applications. In some of the most demanding safety areas including offshore oil and gas and in the nuclear field these systems have to compete with the alternative architecture based on the principle of 2 out of 3 voting. These are known as triple modular redundant or TMR systems. The next diagram illustrates the principle. 

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