AADvance Safety Manual - Tuv-fs.com

AADvance Safety Manualwhere PST euc is the process safety time for the equipment under control.As an example, consider a system function using one sensor and one actuator given thefollowing parameters: PST euc : 20,000ms Sensor delay: 500ms Time for actuator (an ESD valve) to fully operate: 1500msIn this example therefore, the setting of PST for the controller should be less than orequal to 8000ms.Choosing Controller PST SettingsThe response time allocated to a logic solver such as the AADvance controller needsto take account of delays within the operation of sensors and actuators. In addition, thesystem's scan time should be considerably less than the process safety time.The value of the PST shall form part of the safety considerations for the system. Thevalue is defined by the process design authority; the system integrator shall calculateand verify that the process safety time meets the stated requirements. In an AADvance system the PST value is assigned to the system and can beassigned to individual modules. The system PST value is enforced by the processormodules and has priority over the module PST values. When the system PST is notmet the processor modules will fail-safe. The input PST is also enforced by the processor modules; when the PST is notmet, the processors will present fail-safe input values to the application logic. Output PST is enforced by the output modules and when the output PST is notmet, the output module will assume the fail-safe state.Note: The fail-safe state for all AADvance modules is de-energized.You must specify the process safety time for the whole controller. If desired, you canspecify additional process safety times for individual groups of I/O modules. The settingfor the whole controller is a top level setting, which you make once for all the 9110processor modules. Groups of I/O modules can inherit this setting or, if desired, useindividual process safety times instead.Notes: The minimum controller's PST must be at least twice the application scan time. If you choose to specify a process safety time for a group of I/O modules, the I/Omodules use this setting instead of the top level setting. If you do not specify a process safety time for a group of I/O modules, the I/Omodules use the top level setting. If you do not specify any process safety time, the controller will use a default valueof 2,500ms throughout.5-4 Document number 553630 Issue 7: February 2010