The SLS 1508 Logic Solver processes DeltaV SIS modules differently than the DeltaV controller processes other DeltaV modules. All SIS modules in a Logic Solver run at the same scan rate. The scan rate is configurable from 50 to 200 milliseconds in 50 millisecond increments.
On download, the Logic Solver estimates the maximum possible execution time for the SIS modules based on their complexity (number of inputs, expressions, and so on). Note that the estimated maximum execution time can be much greater than the actual ExecTime reported in DeltaV Diagnostics. The estimated maximum execution time is not reported.
If the configured scan rate is less than the estimated maximum execution time, the Logic Solver sets the scan rate to the next slower scan rate. The Logic Solver also sets the Module not executing at configured scan rate bit in the module parameter SIF_ERRORS and activates the standard Logic Solver alarm MAINT_ALM. DeltaV Diagnostics Explorer shows the actual scan rate in the ActualScanTime parameter at the Logic Solver (SLS) level. To clear the alarm, change the configured scan rate to the actual scan rate and re-download.
If the total estimated SIS module execution time exceeds 200 milliseconds, the Logic Solver does not apply the downloaded script and the download fails.
The order of Logic Solver I/O and module processing is also different compared to DeltaV controllers and other DeltaV modules:
Prior to running the SIS modules, every Logic Solver stores a snapshot of all input data in an internal database.
Every Logic Solver executes its contained modules and transmits any secure parameter data. Secure parameters to be published globally are forwarded to the SISNet repeaters.
Every Logic Solver transmits its I/O data to other Logic Solvers on the SIS Local Peer Bus.
The SISNet Repeater forwards any secure parameters generated on the SIS Local Peer Bus.
The SISNet Repeater transmits secure parameters to other SIS Local Peer Busses.