20.08.2019
 Electrical Safety Essay

ItВ isВ veryВ obviousВ fromВ theВ commentsВ postedВ inВ thisВ threadВ thatВ theВ peopleВ drivingВ theВ useВ ofВ theВ RaspberryВ­PiВ asВ aВ PLCВ trainingВ toolВ haveВ notВ conductedВ anyВ professional, В electricalВ andВ electronicВ engineeringВ researchВ intoВ theВ designВ criteriaВ requiredВ forВ anВ educationalВ PLCВ orВ areВ preparedВ toВ acknowledgeВ theВ legallyВ requiredВ EuropeanВ UnionВ safetyВ complianceВ toВ IEC61508В andВ IECВ 61131В­3. В

AВ PLC'sВ functionalВ criterionВ isВ anВ industrialВ controlВ deviceВ usedВ toВ automateВ electricallyВ drivenВ machinery. В TheВ objectiveВ ofВ anyВ realВ worldВ PLCВ designВ andВ trainingВ criterionВ isВ toВ writeВ andВ testВ PLCВ programsВ compliantВ toВ IECВ 61508В andВ IECВ 61131В­3. В BeingВ ableВ toВ simulateВ watchdogВ timerВ failureВ inВ bothВ softwareВ andВ hardwareВ toВ IECВ 61508В andВ IECВ 61131В­3В inВ theВ classroomВ educationalВ environmentВ isВ alsoВ paramountВ toВ anyВ professionalВ PLCВ trainingВ course. В

ThereforeНѕВ forВ classroomВ trainingВ purposes, В aВ PLCВ usedВ toВ emulateВ realВ worldВ functionalityВ requiresВ threeВ levelsВ ofВ watchdogВ complianceВ andВ theВ provisionВ toВ connectВ theВ PLCВ toВ realВ worldВ electricallyВ independentВ failsafeВ simulationВ circuitsВ usingВ aВ lowВ voltageВ powerВ supply, В usuallyВ 24В voltsВ ACВ andВ DC. В

FirstВ Level – AnВ IEC61508В andВ IECВ 61131В­3В complaintВ machineВ languageВ operatingВ systemВ containingВ aВ softwareВ watchdogВ timerВ programmedВ inВ pureВ machineВ languageВ andВ burntВ inВ aВ nonВ­volatileВ ROM. В TheВ purposeВ ofВ theВ CPUВ watchdogВ timerВ isВ toВ monitorВ allВ CPUВ memoryВ functionsВ forВ checksumВ errorsВ andВ watchdogВ failsafeВ onВ anyВ errorВ generated. В

SecondВ Level – AnВ IEC61508В andВ IECВ 61131В­3В complaintВ PLCВ willВ alsoВ containВ anВ externalВ electronicВ hardwareВ watchdogВ circuitВ independentВ ofВ theВ FirstВ LevelВ operations. В TheВ secondВ levelВ watchdog'sВ purposeВ isВ toВ monitorВ theВ PLCВ inputВ andВ outputВ (I/O)В electronics. В InВ theВ eventВ thatВ anyВ I/OВ deviceВ malfunctions, В theВ secondaryВ watchdogВ deВ­energisesВ allВ PLCВ outputs. В

ThirdВ Level – AnВ IEC61508В andВ IECВ 61131В­3В complaintВ PLCВ programВ andВ PLCВ...