HIMax Safety Manual - Tuv-fs.com

3 Safety Concept for Using the PES HIMaxDefective modules can be replaced during operation. To do this, the defective module isremoved from the base plate, and a new module is inserted. The new module automaticallystarts operation. A new processor module assumes the user program from the redundantprocessor module and is thus quickly ready for operation.3.2 Time Parameters Important for SafetyThese are:• Fault Tolerance Time• Watchdog Time• Safety Time• Response Time3.2.1 Fault Tolerance Time (FTT)The fault tolerance time (FTT) is a property of the process and describes the span of timeduring which the process allows faulty signals to exist before the system state becomesdangerous. A dangerous state can result if the fault exists for longer than the FTT.3.2.2 Resource Watchdog TimeThe watchdog time is set in the dialog for configuring the resource properties. This time isthe maximum permissible duration of a RUN cycle (cycle time). If the cycle time exceedsthe preset watchdog time, the processor module adopts the error stop state.When determining the watchdog time, the following factors must be taken into account:• Time required by the application, e.g., the duration of a cycle in the user program.• Time required to manage the redundant processor modules.• Time required to perform a reload.The setting range for the watchdog time of the resource rangesfrom 2 ms to maximum 50 000 ms.The default setting is 200 ms.When setting the watchdog time, the following must apply: watchdog time ≤ ½ * safety timeThe watchdog time for a project is determined by a test on a complete system. During thetest, all the processor modules are inserted in the base plate. The system operates in RUNmode with full load.All communication links are operating (safeethernet and standard protocols).To determine the watchdog time1. Set the watchdog time high for testing.2 Use the system under the maximum load: In the process read the cycle time in theControl Panel and note the variations of the cycle time.3. Remove and re-insert the processor module. To do this, choose the processor modulethat is located furthermost from Slot 3 in Base Plate 0.4 In the diagnostic history, determine the synchronization time from n to n+1 processormodules.5 Calculate the watchdog time fromsynchronization time + 12 ms spare + spare for the noted variations of the cycle time.By this, a suitable value for the watchdog time is determined.Page 18 of 70HI 801 003 D Rev.2.0