The CSLS processes DeltaV SIS modules differently than the DeltaV controller processes other DeltaV modules. All DeltaV SIS modules in a CSLS run at the same scan rate. The scan rate is configurable from 50 to 200 milliseconds in 50 millisecond increments.
On download, the CSLS 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 CSLS sets the scan rate to the next slower scan rate. The CSLS also sets the SIS Module not executing at configured scan rate bit in the SIS module parameter SIF_ERRORS and activates the standard CSLS alarm MAINT_ALM. DeltaV Diagnostics Explorer shows the actual scan rate in the ActualScanTime parameter at the CSLS level. To clear the alarm, change the configured scan rate to the actual scan rate and re-download.
The DeltaV Controller Load Estimator has a Safety Instrumented System (SIS) function blocks reference table which displays execution time and memory usage in CSLSs and controllers. The tool can help you decide how many CSLSs you need and how to best assign SIS modules to CSLSs.
If the total estimated SIS module execution time exceeds 200 milliseconds, the CSLS does not apply the downloaded script and the download fails.