What is the major difference between TMR and QMR technologies? What are the factors influencing in selection of above technolgies?
1. TMR works in 2 out of 3 Voting
QMR works in 2 out of 4 Voting.
2. Both are SIL3 suitable.
3. Diagnostic may be little stronger in QMR.
4. Normally I/O is redunant by configuration in QMR, whereas in TMR I/O may be inbuilt TMR or triplicated.
5. Sources: QMR: Honeywell, Siemens
TMR: Triconex, ICS
I don't think QMR is better than TMR. the only reason is that it works in the principle of two dual redundant plc being made redundant again. so more you increase the dependencies by complicating the system you have to calculate the PFD (probability of failure) on demand of each component. as in QMR you have to consider PFDs for two dual redundant PLC then PFD for the link. so if the link fails the you are left with redundant plcs 1oo2D mode. while in TMR you have three CPUs running for the same cause and giving you the output. if one fails you still be with 2 but the voting will be 2oo2D type.