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

Module Diagnostics 43Module DiagnosticsEach system component detects and reports operational faults.Digital Input ModulesDigital Input Module points typically use a combination of comparison and forceto-valuediagnostics (FVD). Under system control, each channel is independentlycompared against the measured value of all channels. If a mismatch is found, analarm is set. Using the integral FVD capability, each point can be independentlyverified for its ability to accurately detect a transition to the opposite state. Achannel that has detected a fault on a digital input point votes that point to be deenergized.These diagnostics are executed independently by each channel, thusassuring nearly 100% fault coverage and fail-safe operation under all single-fault,and most common, multiple-fault scenarios.Digital Input Module AlarmsDigital Input Module faults are reported to the control program, and these alarmscan be used to increase availability during specific multiple fault conditions. Lossof logic power is reported to the control program.Digital Output ModulesDigital Output Modules use output voter diagnostics (OVD). Under systemcontrol, each output point is commanded sequentially to both the energized and deenergizedstates and the forced state is maintained until the value is detected by thesystem or a time-out occurs (500 microseconds, typical; 2 milliseconds, worstcase). Using the integral OVD capability, each point can be independently verifiedfor its ability to a transition to either state. The OVD is executed in TMR mode,thus assuring nearly 100% fault coverage and fail-safe operation under all singlefaultscenarios.Digital Output Module AlarmsDigital Output Module faults are reported to the control program and can be usedto increase availability during specific multiple fault conditions. Loss of fieldpower or logic power is reported to the control program.The inability of a Digital Output Module to control an output point is reported tothe control program as a Load/Fuse alarm. This condition can result from a loss ofChapter 3Fault Management