Safety Considerations Guide, Tricon v9.0 - Tuv-fs.com

Important TriStation Commands 51Important TriStation CommandsDownload ChangeSeveral commands in TriStation 1131 Developer’s Workbench are of specialinterest when developing a safety application:• Download Change• Upload and Verify• Compare to Last DownloadThe Download Change command is a convenient means of making simplemodifications to an off-line system during application development.! WARNINGDownload Change is intended for off-line use during application development. Ifyou use Download Change to modify a safety-critical application that is runningon-line, you must exercise extreme caution because an error in the modifiedapplication or system configuration may cause a trip or unpredictable behavior.If you must make on-line changes to a controller, you should always follow theguidelines provided in TriStation 1131 Developer's Guide and fully understand therisks you are taking by using the Download Change command.Before a Download Change, use the Diagnostic Panel to verify that Scan Surplusis sufficient for the application and changes being made. As a rule, the value forScan Surplus should be at least 10% of Scan Time to accommodate newly addedelements. For more information on scan time, see “Setting Scan Time” on page 53.! CAUTIONDo not attempt a Download Change if you have a negative Scan Surplus. First,adjust Scan Time to make the surplus value greater than or equal to zero.For more information on the Download Change command, see the TriStation 1131Developer's Guide.Chapter 4Application Development