If you have Yokogawa Centum CS3000 DCS, I would recommend Prosafe. Prosafe has VNet or VNet/IP interface that allows direct communication with Yokogawa.
Similarly, with DeltaV Emerson has introduced its own system for critical applications.
With Invensys, Tricon is preferred. Even in a stand-alone configuration Tricon (Triconex is a subsidiary of Invensys) is a very reliable system.
Triplex Trusted has many nice features such as 1 ms. SOE for contact inputs, line detction modules that can differentiate between the following conditions:
* open contat
* closed contact
* shorted field wiring
* open field wiring
Many of the concepts in Trusted are far more advanced than the other systems. However, the versions of Trusted systems that I worked on had problems such as false nuisance alarms on voting-mismatch. I hope these are rectified in the firmware upgrades.
If reliability, maintainability and ease of programming are the main criteria, I shall recommend Tricon.
