The DeltaV SLS 1508 SIS system supports redundant Logic Solver cards. A redundant Logic Solver consists of a pair of Logic Solver cards mounted in adjacent carrier slots with a redundant terminal block. Each Logic Solver card is powered separately. The Logic Solver cards contain the same configuration, run the logic in lock-step and read and write I/O. The card that is active (as indicated by the Active LED) communicates with the controller on the local bus.
If a Logic Solver card detects a problem, it initiates a reset and de-energizes its outputs. The partner Logic Solver card continues to drive outputs and communicates with the controller as the active card.
You can initiate a manual switchover in Diagnostics from the Logic Solver Switchover context menu. The SIS_DIAGNOSTIC_SWITCHOVER security key is required by default.
In the event of a manual or automatic switchover, the system generates a Logic Solver hardware alarm indicating: Partner Not Available, and Card Not Communicating while the former active Logic Solver is powering-up and obtaining configuration. In addition, a switchover event is reported in the Event Chronicle along with the Logic Solver Maintenance alarms.
A Logic Solver switchover is not disruptive to the process. However, following a switchover, the formerly active card may not be available for approximately two minutes. In other words, it is temporarily not available to take over as the active card.
Redundant Logic Solver cards allow proof testing to occur without affecting a running process. A proof test causes a Logic Solver card to run its power-up test while the partner card is active in order to validate that there are no dangerous, undetected faults present.
There are two types of proof test: manual and automatic. An automatic proof test occurs at user-specified intervals. Set the interval using the Logic Solver properties dialog in DeltaV Explorer. To initiate a manual proof test, use the appropriate Force Reset command on the Logic Solver context menu in Diagnostics.