FUNCTION BLOCKS EXECUTION SCHEDULING METHOD IN EPA INDUSTRIAL ETHERNET

Ning Liu, Chongquan Zhong, and Tonglong Xue

References

  1. [1] I. Draganjac and T. Petrovic, Highly-scalable traffic man-agement of autonomous industrial transportation systems,Robotics and Computer-Integrated Manufacturing, 63(1), 2020,169–182.
  2. [2] D. Aslan and Y. Altintas, Prediction of cutting forces in five-axismilling using feed drive current measurements, IEEE/ASMETransactions on Mechatronics, 23(2), 2018, 833–844.
  3. [3] S. Kayalvizhi and D.M. Vinod Kumar, Planning of au-tonomous microgrid with energy storage using grid-basedmulti-objective harmony search algorithm, International Jour-nal of Power and Energy Systems, 37(1), 2017, 10–18. DOI:10.2316/Journal.203.2017.1.203-6276.
  4. [4] IEC/TR 61158-1, Digital data communication for measurementand control – Fieldbus for use in industrial control systems– Part 1: Overview and guidance (Geneva, Switzerland:International Electrotechnical Commission, 2007).
  5. [6]–[14] Research on the application method of EPA systemapplication in specific engineering fieldEquipment [15]–[19] Research on the development method of EPA equipment anddevelopment system based on specific software and hardware platformPerformance [20], [21] Research on the performance of EPA and propose theimprovement methods to improve the performancedata through EPA communication, and the subsequent FBcan be effectively executed only after receiving the data.Therefore, the execution of FBs must be synchronized withEPA communication to ensure the communication perfor-mance and operation efficiency of EPA system. However,EPA standard only defines EPA deterministic communica-tion scheduling mechanism but does not define the FBS. Inpractical engineering application, it is found that the fol-lowing problems exist in EPA industrial Ethernet system.According to EPA deterministic communicationscheduling mechanism, the communication cycle of EPAsystem is the preconfigured communication macrocycle,but due to the lack of EPA-FBS mechanism, the actualexecution cycles of FBs in engineering application areEPA devices’ scanning cycles. Therefore, a cycle syn-chronization problem arises. Because the scanning cyclesof EPA devices are generally relatively small, an FB inan EPA device will be executed many times in one EPAcommunication macrocycle. Each time the FB is executed,a message carrying its output data is generated and putinto the messages-sending queue of the device. However,when the communication time slice of the device does notarrive, these messages in the queue cannot be sent, andwhen the communication time slice of the device arrives,these messages will be sent to the subsequent FB in turnaccording to the first-in first-out principle. Because thesemessages arrive at the input of the same FB, the old datawill be covered by the new data and cannot be processed.This problem increases the communication load of EPAsystem unnecessarily.According to the previous discussion, it is very nec-essary to propose an FBS method to realize the synchro-nization between the execution of FBs and data commu-nication in EPA system. In [22], [23], the asynchronousproblem between the execution scheduling of FBs and datacommunication in EPA industrial Ethernet was studied,and the synchronization methods were proposed. However,the methods change EPA deterministic communicationscheduling mechanism that is defined in the EPA standardand has been widely used in the equipment of engineeringfield. Therefore, the equipment realizing the methods can-not interoperate with normal EPA equipment in practicalengineering applications. In this article, EPA-FBS methodis proposed that is based on EPA deterministic commu-nication scheduling mechanism and realizes the synchro-nization between the execution scheduling of FBs and datacommunication to improve the real-time performance ofEPA system.2. Ethernet for Plant Automation-Function BlocksExecution Scheduling MethodIn EPA system, each device executes a function task and acommunication task. The function task is the execution ofall the FBs in the device. These FBs have different func-tions and belong to different control loops, but they are allexecuted in sequence with the programme of the device,which is a scheduling unit. The communication task is thetransmission of periodic messages. It executes EPA de-terministic scheduling mechanism and is also a schedulingunit. The control function of an EPA system is achievedby executing the two tasks distributed in many devices inEPA network. EPA-FBS method is to synchronize the twotasks in a device as follows. First, each device in the EPAnetwork is configured with function time slice and commu-nication time slice without interval alternation. Second,functional task and communication task in a device canonly be executed in their own time slices. Third, functiontasks can only be executed once in a function time slice.The schematic diagram of EPA-FBS method is shownas Fig. 1, in which the communication time slice is theperiodic messages transferring time slice, and the rest of themacrocycle is the function time slice. As the function taskis only executed once in its time slice, and the generatedperiodic message can only be sent when the communicationtime slice arrives, the execution of the function task hastwo characteristics as follows. First, a device executesFigure 1. Scheduling diagram of EPA-FBS method.100its function task and communication task alternately andcircularly; moreover, it executes its function task andputs generated messages into the messages-sending queuebefore communication time slice arrives in each macrocycle.Second, the function task can only be executed once ineach EPA macrocycle, so that the communication taskand the function task achieve the cycle synchronizationwith the macrocycle. Therefore, EPA-FBS method canprevent the invalid execution of FBs.3. Parameters of Ethernet for Plant Automation-Function Blocks Execution Scheduling MethodThe parameters related to EPA-FBS method include func-tion time slice F, communication time slice S, non-periodicmessages sending time slice B and macrocycle T. The keyto the success of the method is that the function time sliceis enough to execute the function task. If the functiontime slices of device i is recorded as Fi and the functiontask execution time of device i is recorded as Ci, Fi shouldbe bigger than or equal to Ci, as shown in the followingequation:Fi ≥ Ci (1)According to EPA-FBS method, the relation betweenthe communication time slice Si and the function time sliceFi of device i can be shown as follows:Fi = T − Si (2)According to EPA deterministic scheduling mecha-nism, the macrocycle T is the sum of the non-periodicmessages sending time slice B and the communication timeslices S of all the devices in the network, as shown in thefollowing equation:T =nj=1Sj + B (3)where n is the number of the devices in the EPA network,and Sj is the communication time slice of device j. Insert(3) into (2) and transform, Fi can be shown as follows:Fi =nj=1Sj + B − Si (4)As shown in (4), Fi is equal to the sum of the commu-nication time slice S of each device and the non-periodicmessages transmission time slice B in the network minusthe communication time slices S of device i. Insert (4) into(1) and transform, the following equation can be obtained:nj=1Sj + B − Si ≥ Ci (5)However, in non-periodic messages sending time slice,function task and transmission of non-periodic messagesare executed in parallel. To ensure the successful transmis-sion of non-periodic messages, the priority of non-periodicmessages’ transmission is higher than the function task ina device. Furthermore, the communication load of non-periodic messages in control network is stochastic and dif-ficult to determine in advance. When the communicationload of non-periodic messages is very big, the function taskwill be frequently interrupted and cannot have effectiveand deterministic execution time. Thus, the setting ofthe time slices of EPA-FBS must meet the condition: Ri(function time slice Fi minus non-periodic messages send-ing time slice B) is no less than the function task executiontime Ci of device i, as shown in the following equations:Ri ≥ Ci (6)Ri =nj=1Sj − Si (7)Equations (6) and (7) are the setting conditions of thetime slices of EPA-FBS method.4. RealizationThe key problem of the realization of EPA-FBS method isthe execution of function task. It has three requirements.First, a function task can only be executed in its functiontime slice and can only be executed once. Second, thefunction time slice of a device must be enough to executeits function task. Third, a function task must be executedimmediately once function time slice arrives.The first requirement can be solved by setting schedul-ing tag. Scheduling tag is a logical variable. Each FBhas one scheduling tag. When a device scans its FBs,scheduling tag is the basis whether it executes an FB ornot. If the scheduling tag of the FB is true, the FB willbe executed, otherwise, if it is false, the FB will not beexecuted. During communication time slice, a device setsthe scheduling tags of all the FBs true. Then all the FBswill be executed when function time slice arrives.The execution of function task is shown as Fig. 2, m isthe number of FBs in a device. Mj is the scheduling tagof FBi. When the program scans an FB, if its Mj is false,it skips to scan the next FB. If its Mj is true, it executesthe FB and then sets its Mj to false. By this means,each FB can be executed only once in the task functiontime slice. But when the communication time slice arrives,the programme will set the scheduling tags of all the FBsto true so that the FBs can be executed when the nextfunction time slice arrives.The second requirement can be solved by makingdevices monitor their time slices automatically and sendout alarm messages. When the function task starts, theprogramme obtains current time Lt of the device. Whenthe function task finishes, it obtains current time Lp. ThenCi = Lp − Lt. If Ci ≤ Ri, the time slice is enough toexecute its function task. Otherwise, the time slice is notenough to execute its function task. So the device sendsalarm messages to apply for resetting the time slices.101Figure 2. Execution of function.The third requirement can be solved using timer’sinterrupt. The programme sets a timer that triggers aninterrupt when communication time slice or function timeslice arrives. EPA-FBS method is realized in the interrupthandler of the timer. The interrupt handler is shown asFig. 3. When the interrupt is triggered, device i obtaincurrent time Lt to determine whether current time is in thecommunication time slice or not according to the followingequation:G =⎧⎨⎩Di ≤ MOD(Lt, T) ≺ Ds i = nDi ≤ MOD(Lt, T) ≺ Di+1 i = n(8)Therein, Di is the periodic-data-sending offsets of de-vice i, and Di+1 is the periodic-data-sending offsets ofdevice i+1. Ds is the non-periodic-data-sending offset ofthe network. G is a logical variable that indicates whethercurrent time is in the communication time slice or not.If G is true, current time is in the communication timeslice. The device calculates the start time of function timeslice and updates the timer then sets scheduling tags of allthe FBs in the device to true and then sends out periodicmessages. If G is false, current time is in the function timeslice. The device calculates the start time of communica-tion time slice and updates the timer and then scans andexecutes FBs.In addition, to ensure the transmission of non-periodicmessage, a timer for the transmission of non-periodic mes-sages is set. When the start time of the non-periodicmessages time slice arrives, the timer triggers an interruptand the interrupt handler calculates the start time of nextnon-periodic messages sending time slice and updates thetimer and then sends out non-periodic messages.Figure 3. Flow chart of interrupt handler of function tasktimer.Figure 4. Experiment platform.5. ExperimentIn this section, an experiment is conducted to verify theeffect of EPA-FBS method. As shown in Fig. 4, theexperimental platform is made up of a personal computer(PC), an EPA bridge and an EPA network, including aHUB, a TE (test equipment) and four DUTs (devices undertest). The DUTs and TE are EPA control modules. EPA-FBS method is realized in their protocol stack. The TE102Figure 5. Function diagram.Table 2Configuration of Communication Time Slice andAdjustment LimitDUT Di Sa Sb Ds Ba Bb T(ms) (ms) (ms) (ms) (ms) (ms) (ms)1 0 0.2 22 2 0.2 23 4 0.2 24 6 0.2 29 1 1 10TE 8 0.5 0.5Port 8.5 0.5 0.5runs a specific programme for monitoring and analysingmessage transmission in the network. EPA-FBS methodand EPA-timeslice self-adaptive adjustment (TSA) methodproposed in [20] are realized in the communication protocolstack in the DUTs and TE. The EPA Bridge is used toforward the messages between the network and the PC.The PC runs a configuration and analysis software toconfigure the system and process experimental data.As shown in Fig. 5, 20 FBs distributed in the 4DUTs are connected into 5 control loops. After applicationof EPA-FBS method, DUT1 sends two messages, DUT2sends one message, DUT3 sends three messages and DUT4sends one message in each macrocycle. The messages areEPA periodic messages whose sizes are 74 bytes. Beforethe application of EPA-FBS method, the execution timesof function task in each macrocycle depend on the scanningcycle of each DUT and the number of messages thateach DUT needs to send in each macrocycle depends onthe scanning times. By comparing the communicationtime slice between before and after application of EPA-FBS method, the effect of EPA-FBS method to reducecommunication load and execution times of FBs can beobtained.The initial values of the periodic-data-sending offsetsDi and the non-periodic-data-sending time slice Ds, theallowable extreme values Sa and Sb of communication timeslice, the allowable extreme values Ba and Bb and theFigure 6. Time slices comparison before and after applica-tion of EPA-FBS method.Figure 7. Network delays comparison of control loops be-fore and after application of EPA-FBS method.macrocycle T are shown in Table 2. The non-periodicmessages sending time slice, the communication time slicesof TE and testing port are locked so as to prevent the ex-perimental results from being disturbed. The TE obtainsthe communication time slices of all the DUTs and thenon-periodic messages sending time slice of the network ineach macrocycle by means of receiving and processing theNDA (non-periodic data annunciation) messages. ThenTE transmits the data to the configuration and analysissoftware in the PC through the EPA network. The config-uration and analysis software running in the PC receivesand processes the data and makes the average of the timeslices from 100 macrocycles to display.In Fig. 6, the communication time slices Si and thenon-periodic messages sending time slice B before and afterapplication of EPA-FBS method are shown. Before theapplication of EPA-FBS, the communication time slices arevery big. The communication time slices of the DUT1 andthe DUT3 reach their maximum: 2 mm. While after theapplication of EPA-FBS, the communication time slicesof DUT1–DUT4 reduce 67.6%, 61.2%, 61.8% and 65.4%,respectively, and the macrocycle reduces 48.8%. The morecommunication times a device need, the more obviousthe effect of the reducing communication time slice is. Thereduction of the communication time slices reflects thereduction of the communication load [20]. Combined withthe previous content, the experimental results show thatthe execution times of FBs are reduced. The reductionof the execution times of FBs means the reduction of thecalculation load of the EPA system so that the operationefficiency can be improved.Moreover, as shown in Fig. 7, after the applicationof EPA-FBS method, the network delays of control loop1031–control loop 5 reduce 46.2%, 44.9%, 43.1%, 43.1% and67.5%, respectively. Thus, the experiment shows thatEPA-FBS can improve the real-time performance of EPAsystem.6. ConclusionIn this article, a method to improve the real-time perfor-mance of EPA industrial Ethernet is proposed on the baseof EPA deterministic scheduling mechanism. The methodintegrates all the FBs in a single-field device into a functiontask and sets the function time slice for the execution ofthe function task according to the principle of the cyclesynchronization between the execution of FBs and the datacommunication in EPA system. On this basis, the methodfirst realizes the single execution of each device’s functiontask in an EPA macrocycle by setting a scheduling tag ineach FB and then realizes the quick trigger execution ofthe function task when its time slice arrives by using timerinterrupt. By the previous means, the method realizes thesynchronization between the execution scheduling of FBsand EPA deterministic communication so that it preventsthe invalid executions of FBs in EPA system. The ex-periment proves that the method reduces the communica-tion load and improves the real-time performance of EPAsystem.AcknowledgementThe work reported in this article was funded jointly by twoprojects, which are the project of national science and tech-nology supporting plan of China (No. 2015BAF20B02).References[1] I. Draganjac and T. Petrovic, Highly-scalable traffic man-agement of autonomous industrial transportation systems,Robotics and Computer-Integrated Manufacturing, 63(1), 2020,169–182.[2] D. Aslan and Y. Altintas, Prediction of cutting forces in five-axismilling using feed drive current measurements, IEEE/ASMETransactions on Mechatronics, 23(2), 2018, 833–844.[3] S. Kayalvizhi and D.M. Vinod Kumar, Planning of au-tonomous microgrid with energy storage using grid-basedmulti-objective harmony search algorithm, International Jour-nal of Power and Energy Systems, 37(1), 2017, 10–18. DOI:10.2316/Journal.203.2017.1.203-6276.[4] IEC/TR 61158-1, Digital data communication for measurementand control – Fieldbus for use in industrial control systems– Part 1: Overview and guidance (Geneva, Switzerland:International Electrotechnical Commission, 2007).[5] IEC61784-2, Industrial communication networks – Profiles –Part 2: Additional fieldbus profiles for real-time networksbased on ISO/IEC 8802-3 (Geneva, Switzerland: InternationalElectrotechnical Commission, 2007).[6] J. Wang, C. Xu, and W. Sun, Mine fully mechanized monitoringsystem of multiple fieldbus based on EPA standard, Coal MineMachinery, 37(12), 2016, 177–182.
  6. [7] H. Wang, G. Wu, and P. Wang, Application of DRP insmart substation based on EPA, Automation of Electric PowerSystems, 36(17), 2012, 77–81.
  7. [8] X. Zhu, Research on real-time Ethernet technique acceptablefor digital substations, Guangdong Electric Power, 24(10),2011, 48–52.
  8. [9] D. Mestriner and M. Invernizzi. Analysis of lightning ef-fects on power plant connection, International Journal ofPower and Energy Systems, 38(2), 2018, 40–49. DOI: 10.2316/Journal.203.2018.2.203-0011.
  9. [10] W. Wang, B. Yang, and C. Shi, Development of EPA elec-tric actuator based on small embedded RTOS, InstrumentTechnique and Sensor, 46(8), 2010, 22–29.
  10. [11] X. Wang, X. Hu, and Y. Zhang, Design and research oflow-voltage DC Servo with EPA, Computer Engineering andApplications, 46(19), 2010, 58–66.
  11. [12] H. Li, H. Zhang, and D. Peng, Design and application ofcommunication gateway of EPA and MODBUS on electricpower system, Energy Procedia, 02(17), 2012, 286–292.
  12. [14] Research on the application method of EPA systemapplication in specific engineering fieldEquipment
  13. [15]–[19] Research on the development method of EPA equipment anddevelopment system based on specific software and hardware platformPerformance [20], [21] Research on the performance of EPA and propose theimprovement methods to improve the performancedata through EPA communication, and the subsequent FBcan be effectively executed only after receiving the data.Therefore, the execution of FBs must be synchronized withEPA communication to ensure the communication perfor-mance and operation efficiency of EPA system. However,EPA standard only defines EPA deterministic communica-tion scheduling mechanism but does not define the FBS. Inpractical engineering application, it is found that the fol-lowing problems exist in EPA industrial Ethernet system.According to EPA deterministic communicationscheduling mechanism, the communication cycle of EPAsystem is the preconfigured communication macrocycle,but due to the lack of EPA-FBS mechanism, the actualexecution cycles of FBs in engineering application areEPA devices’ scanning cycles. Therefore, a cycle syn-chronization problem arises. Because the scanning cyclesof EPA devices are generally relatively small, an FB inan EPA device will be executed many times in one EPAcommunication macrocycle. Each time the FB is executed,a message carrying its output data is generated and putinto the messages-sending queue of the device. However,when the communication time slice of the device does notarrive, these messages in the queue cannot be sent, andwhen the communication time slice of the device arrives,these messages will be sent to the subsequent FB in turnaccording to the first-in first-out principle. Because thesemessages arrive at the input of the same FB, the old datawill be covered by the new data and cannot be processed.This problem increases the communication load of EPAsystem unnecessarily.According to the previous discussion, it is very nec-essary to propose an FBS method to realize the synchro-nization between the execution of FBs and data commu-nication in EPA system. In [22], [23], the asynchronousproblem between the execution scheduling of FBs and datacommunication in EPA industrial Ethernet was studied,and the synchronization methods were proposed. However,the methods change EPA deterministic communicationscheduling mechanism that is defined in the EPA standardand has been widely used in the equipment of engineeringfield. Therefore, the equipment realizing the methods can-not interoperate with normal EPA equipment in practicalengineering applications. In this article, EPA-FBS methodis proposed that is based on EPA deterministic commu-nication scheduling mechanism and realizes the synchro-nization between the execution scheduling of FBs and datacommunication to improve the real-time performance ofEPA system.2. Ethernet for Plant Automation-Function BlocksExecution Scheduling MethodIn EPA system, each device executes a function task and acommunication task. The function task is the execution ofall the FBs in the device. These FBs have different func-tions and belong to different control loops, but they are allexecuted in sequence with the programme of the device,which is a scheduling unit. The communication task is thetransmission of periodic messages. It executes EPA de-terministic scheduling mechanism and is also a schedulingunit. The control function of an EPA system is achievedby executing the two tasks distributed in many devices inEPA network. EPA-FBS method is to synchronize the twotasks in a device as follows. First, each device in the EPAnetwork is configured with function time slice and commu-nication time slice without interval alternation. Second,functional task and communication task in a device canonly be executed in their own time slices. Third, functiontasks can only be executed once in a function time slice.The schematic diagram of EPA-FBS method is shownas Fig. 1, in which the communication time slice is theperiodic messages transferring time slice, and the rest of themacrocycle is the function time slice. As the function taskis only executed once in its time slice, and the generatedperiodic message can only be sent when the communicationtime slice arrives, the execution of the function task hastwo characteristics as follows. First, a device executesFigure 1. Scheduling diagram of EPA-FBS method.100its function task and communication task alternately andcircularly; moreover, it executes its function task andputs generated messages into the messages-sending queuebefore communication time slice arrives in each macrocycle.Second, the function task can only be executed once ineach EPA macrocycle, so that the communication taskand the function task achieve the cycle synchronizationwith the macrocycle. Therefore, EPA-FBS method canprevent the invalid execution of FBs.3. Parameters of Ethernet for Plant Automation-Function Blocks Execution Scheduling MethodThe parameters related to EPA-FBS method include func-tion time slice F, communication time slice S, non-periodicmessages sending time slice B and macrocycle T. The keyto the success of the method is that the function time sliceis enough to execute the function task. If the functiontime slices of device i is recorded as Fi and the functiontask execution time of device i is recorded as Ci, Fi shouldbe bigger than or equal to Ci, as shown in the followingequation:Fi ≥ Ci (1)According to EPA-FBS method, the relation betweenthe communication time slice Si and the function time sliceFi of device i can be shown as follows:Fi = T − Si (2)According to EPA deterministic scheduling mecha-nism, the macrocycle T is the sum of the non-periodicmessages sending time slice B and the communication timeslices S of all the devices in the network, as shown in thefollowing equation:T =nj=1Sj + B (3)where n is the number of the devices in the EPA network,and Sj is the communication time slice of device j. Insert(3) into (2) and transform, Fi can be shown as follows:Fi =nj=1Sj + B − Si (4)As shown in (4), Fi is equal to the sum of the commu-nication time slice S of each device and the non-periodicmessages transmission time slice B in the network minusthe communication time slices S of device i. Insert (4) into(1) and transform, the following equation can be obtained:nj=1Sj + B − Si ≥ Ci (5)However, in non-periodic messages sending time slice,function task and transmission of non-periodic messagesare executed in parallel. To ensure the successful transmis-sion of non-periodic messages, the priority of non-periodicmessages’ transmission is higher than the function task ina device. Furthermore, the communication load of non-periodic messages in control network is stochastic and dif-ficult to determine in advance. When the communicationload of non-periodic messages is very big, the function taskwill be frequently interrupted and cannot have effectiveand deterministic execution time. Thus, the setting ofthe time slices of EPA-FBS must meet the condition: Ri(function time slice Fi minus non-periodic messages send-ing time slice B) is no less than the function task executiontime Ci of device i, as shown in the following equations:Ri ≥ Ci (6)Ri =nj=1Sj − Si (7)Equations (6) and (7) are the setting conditions of thetime slices of EPA-FBS method.4. RealizationThe key problem of the realization of EPA-FBS method isthe execution of function task. It has three requirements.First, a function task can only be executed in its functiontime slice and can only be executed once. Second, thefunction time slice of a device must be enough to executeits function task. Third, a function task must be executedimmediately once function time slice arrives.The first requirement can be solved by setting schedul-ing tag. Scheduling tag is a logical variable. Each FBhas one scheduling tag. When a device scans its FBs,scheduling tag is the basis whether it executes an FB ornot. If the scheduling tag of the FB is true, the FB willbe executed, otherwise, if it is false, the FB will not beexecuted. During communication time slice, a device setsthe scheduling tags of all the FBs true. Then all the FBswill be executed when function time slice arrives.The execution of function task is shown as Fig. 2, m isthe number of FBs in a device. Mj is the scheduling tagof FBi. When the program scans an FB, if its Mj is false,it skips to scan the next FB. If its Mj is true, it executesthe FB and then sets its Mj to false. By this means,each FB can be executed only once in the task functiontime slice. But when the communication time slice arrives,the programme will set the scheduling tags of all the FBsto true so that the FBs can be executed when the nextfunction time slice arrives.The second requirement can be solved by makingdevices monitor their time slices automatically and sendout alarm messages. When the function task starts, theprogramme obtains current time Lt of the device. Whenthe function task finishes, it obtains current time Lp. ThenCi = Lp − Lt. If Ci ≤ Ri, the time slice is enough toexecute its function task. Otherwise, the time slice is notenough to execute its function task. So the device sendsalarm messages to apply for resetting the time slices.101Figure 2. Execution of function.The third requirement can be solved using timer’sinterrupt. The programme sets a timer that triggers aninterrupt when communication time slice or function timeslice arrives. EPA-FBS method is realized in the interrupthandler of the timer. The interrupt handler is shown asFig. 3. When the interrupt is triggered, device i obtaincurrent time Lt to determine whether current time is in thecommunication time slice or not according to the followingequation:G =⎧⎨⎩Di ≤ MOD(Lt, T) ≺ Ds i = nDi ≤ MOD(Lt, T) ≺ Di+1 i = n(8)Therein, Di is the periodic-data-sending offsets of de-vice i, and Di+1 is the periodic-data-sending offsets ofdevice i+1. Ds is the non-periodic-data-sending offset ofthe network. G is a logical variable that indicates whethercurrent time is in the communication time slice or not.If G is true, current time is in the communication timeslice. The device calculates the start time of function timeslice and updates the timer then sets scheduling tags of allthe FBs in the device to true and then sends out periodicmessages. If G is false, current time is in the function timeslice. The device calculates the start time of communica-tion time slice and updates the timer and then scans andexecutes FBs.In addition, to ensure the transmission of non-periodicmessage, a timer for the transmission of non-periodic mes-sages is set. When the start time of the non-periodicmessages time slice arrives, the timer triggers an interruptand the interrupt handler calculates the start time of nextnon-periodic messages sending time slice and updates thetimer and then sends out non-periodic messages.Figure 3. Flow chart of interrupt handler of function tasktimer.Figure 4. Experiment platform.5. ExperimentIn this section, an experiment is conducted to verify theeffect of EPA-FBS method. As shown in Fig. 4, theexperimental platform is made up of a personal computer(PC), an EPA bridge and an EPA network, including aHUB, a TE (test equipment) and four DUTs (devices undertest). The DUTs and TE are EPA control modules. EPA-FBS method is realized in their protocol stack. The TE102Figure 5. Function diagram.Table 2Configuration of Communication Time Slice andAdjustment LimitDUT Di Sa Sb Ds Ba Bb T(ms) (ms) (ms) (ms) (ms) (ms) (ms)1 0 0.2 22 2 0.2 23 4 0.2 24 6 0.2 29 1 1 10TE 8 0.5 0.5Port 8.5 0.5 0.5runs a specific programme for monitoring and analysingmessage transmission in the network. EPA-FBS methodand EPA-timeslice self-adaptive adjustment (TSA) methodproposed in [20] are realized in the communication protocolstack in the DUTs and TE. The EPA Bridge is used toforward the messages between the network and the PC.The PC runs a configuration and analysis software toconfigure the system and process experimental data.As shown in Fig. 5, 20 FBs distributed in the 4DUTs are connected into 5 control loops. After applicationof EPA-FBS method, DUT1 sends two messages, DUT2sends one message, DUT3 sends three messages and DUT4sends one message in each macrocycle. The messages areEPA periodic messages whose sizes are 74 bytes. Beforethe application of EPA-FBS method, the execution timesof function task in each macrocycle depend on the scanningcycle of each DUT and the number of messages thateach DUT needs to send in each macrocycle depends onthe scanning times. By comparing the communicationtime slice between before and after application of EPA-FBS method, the effect of EPA-FBS method to reducecommunication load and execution times of FBs can beobtained.The initial values of the periodic-data-sending offsetsDi and the non-periodic-data-sending time slice Ds, theallowable extreme values Sa and Sb of communication timeslice, the allowable extreme values Ba and Bb and theFigure 6. Time slices comparison before and after applica-tion of EPA-FBS method.Figure 7. Network delays comparison of control loops be-fore and after application of EPA-FBS method.macrocycle T are shown in Table 2. The non-periodicmessages sending time slice, the communication time slicesof TE and testing port are locked so as to prevent the ex-perimental results from being disturbed. The TE obtainsthe communication time slices of all the DUTs and thenon-periodic messages sending time slice of the network ineach macrocycle by means of receiving and processing theNDA (non-periodic data annunciation) messages. ThenTE transmits the data to the configuration and analysissoftware in the PC through the EPA network. The config-uration and analysis software running in the PC receivesand processes the data and makes the average of the timeslices from 100 macrocycles to display.In Fig. 6, the communication time slices Si and thenon-periodic messages sending time slice B before and afterapplication of EPA-FBS method are shown. Before theapplication of EPA-FBS, the communication time slices arevery big. The communication time slices of the DUT1 andthe DUT3 reach their maximum: 2 mm. While after theapplication of EPA-FBS, the communication time slicesof DUT1–DUT4 reduce 67.6%, 61.2%, 61.8% and 65.4%,respectively, and the macrocycle reduces 48.8%. The morecommunication times a device need, the more obviousthe effect of the reducing communication time slice is. Thereduction of the communication time slices reflects thereduction of the communication load [20]. Combined withthe previous content, the experimental results show thatthe execution times of FBs are reduced. The reductionof the execution times of FBs means the reduction of thecalculation load of the EPA system so that the operationefficiency can be improved.Moreover, as shown in Fig. 7, after the applicationof EPA-FBS method, the network delays of control loop1031–control loop 5 reduce 46.2%, 44.9%, 43.1%, 43.1% and67.5%, respectively. Thus, the experiment shows thatEPA-FBS can improve the real-time performance of EPAsystem.6. ConclusionIn this article, a method to improve the real-time perfor-mance of EPA industrial Ethernet is proposed on the baseof EPA deterministic scheduling mechanism. The methodintegrates all the FBs in a single-field device into a functiontask and sets the function time slice for the execution ofthe function task according to the principle of the cyclesynchronization between the execution of FBs and the datacommunication in EPA system. On this basis, the methodfirst realizes the single execution of each device’s functiontask in an EPA macrocycle by setting a scheduling tag ineach FB and then realizes the quick trigger execution ofthe function task when its time slice arrives by using timerinterrupt. By the previous means, the method realizes thesynchronization between the execution scheduling of FBsand EPA deterministic communication so that it preventsthe invalid executions of FBs in EPA system. The ex-periment proves that the method reduces the communica-tion load and improves the real-time performance of EPAsystem.AcknowledgementThe work reported in this article was funded jointly by twoprojects, which are the project of national science and tech-nology supporting plan of China (No. 2015BAF20B02).References[1] I. Draganjac and T. Petrovic, Highly-scalable traffic man-agement of autonomous industrial transportation systems,Robotics and Computer-Integrated Manufacturing, 63(1), 2020,169–182.[2] D. Aslan and Y. Altintas, Prediction of cutting forces in five-axismilling using feed drive current measurements, IEEE/ASMETransactions on Mechatronics, 23(2), 2018, 833–844.[3] S. Kayalvizhi and D.M. Vinod Kumar, Planning of au-tonomous microgrid with energy storage using grid-basedmulti-objective harmony search algorithm, International Jour-nal of Power and Energy Systems, 37(1), 2017, 10–18. DOI:10.2316/Journal.203.2017.1.203-6276.[4] IEC/TR 61158-1, Digital data communication for measurementand control – Fieldbus for use in industrial control systems– Part 1: Overview and guidance (Geneva, Switzerland:International Electrotechnical Commission, 2007).[5] IEC61784-2, Industrial communication networks – Profiles –Part 2: Additional fieldbus profiles for real-time networksbased on ISO/IEC 8802-3 (Geneva, Switzerland: InternationalElectrotechnical Commission, 2007).[6] J. Wang, C. Xu, and W. Sun, Mine fully mechanized monitoringsystem of multiple fieldbus based on EPA standard, Coal MineMachinery, 37(12), 2016, 177–182.[7] H. Wang, G. Wu, and P. Wang, Application of DRP insmart substation based on EPA, Automation of Electric PowerSystems, 36(17), 2012, 77–81.[8] X. Zhu, Research on real-time Ethernet technique acceptablefor digital substations, Guangdong Electric Power, 24(10),2011, 48–52.[9] D. Mestriner and M. Invernizzi. Analysis of lightning ef-fects on power plant connection, International Journal ofPower and Energy Systems, 38(2), 2018, 40–49. DOI: 10.2316/Journal.203.2018.2.203-0011.[10] W. Wang, B. Yang, and C. Shi, Development of EPA elec-tric actuator based on small embedded RTOS, InstrumentTechnique and Sensor, 46(8), 2010, 22–29.[11] X. Wang, X. Hu, and Y. Zhang, Design and research oflow-voltage DC Servo with EPA, Computer Engineering andApplications, 46(19), 2010, 58–66.[12] H. Li, H. Zhang, and D. Peng, Design and application ofcommunication gateway of EPA and MODBUS on electricpower system, Energy Procedia, 02(17), 2012, 286–292.[13] Y. Cao, Y. Tong, and Y. Tang, Application of EPA real-timeEthernet technology in marine PLC control system, InstrumentStandardization & Metrology, 36(1), 2019, 18–21.[14] S. Luo and J. Huang, Design of integrated control system forbrake valve maintenance based on EPA protocol, TechnologyInnovation and Application, 12(5), 2018, 110–114.[15] Q. Tong and T. Wang, The EPA on-chip communication systemwith AMBA bus, China Instrumentation, 26(4), 2018, 65–70.
  14. [16] R. Shi, Research and implementation of PLC network com-munication function block technology (Dalian, China: DalianUniversity of Technology, 2016).
  15. [17] Y. He, D. Feng, and Y. Zhu, Deterministic transmission of mul-timedia data based on EPA network, Computer Engineering,40(2), 2014, 26–30.
  16. [19] Research on the development method of EPA equipment anddevelopment system based on specific software and hardware platformPerformance
  17. [20],
  18. [21] Research on the performance of EPA and propose theimprovement methods to improve the performancedata through EPA communication, and the subsequent FBcan be effectively executed only after receiving the data.Therefore, the execution of FBs must be synchronized withEPA communication to ensure the communication perfor-mance and operation efficiency of EPA system. However,EPA standard only defines EPA deterministic communica-tion scheduling mechanism but does not define the FBS. Inpractical engineering application, it is found that the fol-lowing problems exist in EPA industrial Ethernet system.According to EPA deterministic communicationscheduling mechanism, the communication cycle of EPAsystem is the preconfigured communication macrocycle,but due to the lack of EPA-FBS mechanism, the actualexecution cycles of FBs in engineering application areEPA devices’ scanning cycles. Therefore, a cycle syn-chronization problem arises. Because the scanning cyclesof EPA devices are generally relatively small, an FB inan EPA device will be executed many times in one EPAcommunication macrocycle. Each time the FB is executed,a message carrying its output data is generated and putinto the messages-sending queue of the device. However,when the communication time slice of the device does notarrive, these messages in the queue cannot be sent, andwhen the communication time slice of the device arrives,these messages will be sent to the subsequent FB in turnaccording to the first-in first-out principle. Because thesemessages arrive at the input of the same FB, the old datawill be covered by the new data and cannot be processed.This problem increases the communication load of EPAsystem unnecessarily.According to the previous discussion, it is very nec-essary to propose an FBS method to realize the synchro-nization between the execution of FBs and data commu-nication in EPA system. In
  19. [22],
  20. [23], the asynchronousproblem between the execution scheduling of FBs and datacommunication in EPA industrial Ethernet was studied,and the synchronization methods were proposed. However,the methods change EPA deterministic communicationscheduling mechanism that is defined in the EPA standardand has been widely used in the equipment of engineeringfield. Therefore, the equipment realizing the methods can-not interoperate with normal EPA equipment in practicalengineering applications. In this article, EPA-FBS methodis proposed that is based on EPA deterministic commu-nication scheduling mechanism and realizes the synchro-nization between the execution scheduling of FBs and datacommunication to improve the real-time performance ofEPA system.2. Ethernet for Plant Automation-Function BlocksExecution Scheduling MethodIn EPA system, each device executes a function task and acommunication task. The function task is the execution ofall the FBs in the device. These FBs have different func-tions and belong to different control loops, but they are allexecuted in sequence with the programme of the device,which is a scheduling unit. The communication task is thetransmission of periodic messages. It executes EPA de-terministic scheduling mechanism and is also a schedulingunit. The control function of an EPA system is achievedby executing the two tasks distributed in many devices inEPA network. EPA-FBS method is to synchronize the twotasks in a device as follows. First, each device in the EPAnetwork is configured with function time slice and commu-nication time slice without interval alternation. Second,functional task and communication task in a device canonly be executed in their own time slices. Third, functiontasks can only be executed once in a function time slice.The schematic diagram of EPA-FBS method is shownas Fig. 1, in which the communication time slice is theperiodic messages transferring time slice, and the rest of themacrocycle is the function time slice. As the function taskis only executed once in its time slice, and the generatedperiodic message can only be sent when the communicationtime slice arrives, the execution of the function task hastwo characteristics as follows. First, a device executesFigure 1. Scheduling diagram of EPA-FBS method.100its function task and communication task alternately andcircularly; moreover, it executes its function task andputs generated messages into the messages-sending queuebefore communication time slice arrives in each macrocycle.Second, the function task can only be executed once ineach EPA macrocycle, so that the communication taskand the function task achieve the cycle synchronizationwith the macrocycle. Therefore, EPA-FBS method canprevent the invalid execution of FBs.3. Parameters of Ethernet for Plant Automation-Function Blocks Execution Scheduling MethodThe parameters related to EPA-FBS method include func-tion time slice F, communication time slice S, non-periodicmessages sending time slice B and macrocycle T. The keyto the success of the method is that the function time sliceis enough to execute the function task. If the functiontime slices of device i is recorded as Fi and the functiontask execution time of device i is recorded as Ci, Fi shouldbe bigger than or equal to Ci, as shown in the followingequation:Fi ≥ Ci (1)According to EPA-FBS method, the relation betweenthe communication time slice Si and the function time sliceFi of device i can be shown as follows:Fi = T − Si (2)According to EPA deterministic scheduling mecha-nism, the macrocycle T is the sum of the non-periodicmessages sending time slice B and the communication timeslices S of all the devices in the network, as shown in thefollowing equation:T =nj=1Sj + B (3)where n is the number of the devices in the EPA network,and Sj is the communication time slice of device j. Insert(3) into (2) and transform, Fi can be shown as follows:Fi =nj=1Sj + B − Si (4)As shown in (4), Fi is equal to the sum of the commu-nication time slice S of each device and the non-periodicmessages transmission time slice B in the network minusthe communication time slices S of device i. Insert (4) into(1) and transform, the following equation can be obtained:nj=1Sj + B − Si ≥ Ci (5)However, in non-periodic messages sending time slice,function task and transmission of non-periodic messagesare executed in parallel. To ensure the successful transmis-sion of non-periodic messages, the priority of non-periodicmessages’ transmission is higher than the function task ina device. Furthermore, the communication load of non-periodic messages in control network is stochastic and dif-ficult to determine in advance. When the communicationload of non-periodic messages is very big, the function taskwill be frequently interrupted and cannot have effectiveand deterministic execution time. Thus, the setting ofthe time slices of EPA-FBS must meet the condition: Ri(function time slice Fi minus non-periodic messages send-ing time slice B) is no less than the function task executiontime Ci of device i, as shown in the following equations:Ri ≥ Ci (6)Ri =nj=1Sj − Si (7)Equations (6) and (7) are the setting conditions of thetime slices of EPA-FBS method.4. RealizationThe key problem of the realization of EPA-FBS method isthe execution of function task. It has three requirements.First, a function task can only be executed in its functiontime slice and can only be executed once. Second, thefunction time slice of a device must be enough to executeits function task. Third, a function task must be executedimmediately once function time slice arrives.The first requirement can be solved by setting schedul-ing tag. Scheduling tag is a logical variable. Each FBhas one scheduling tag. When a device scans its FBs,scheduling tag is the basis whether it executes an FB ornot. If the scheduling tag of the FB is true, the FB willbe executed, otherwise, if it is false, the FB will not beexecuted. During communication time slice, a device setsthe scheduling tags of all the FBs true. Then all the FBswill be executed when function time slice arrives.The execution of function task is shown as Fig. 2, m isthe number of FBs in a device. Mj is the scheduling tagof FBi. When the program scans an FB, if its Mj is false,it skips to scan the next FB. If its Mj is true, it executesthe FB and then sets its Mj to false. By this means,each FB can be executed only once in the task functiontime slice. But when the communication time slice arrives,the programme will set the scheduling tags of all the FBsto true so that the FBs can be executed when the nextfunction time slice arrives.The second requirement can be solved by makingdevices monitor their time slices automatically and sendout alarm messages. When the function task starts, theprogramme obtains current time Lt of the device. Whenthe function task finishes, it obtains current time Lp. ThenCi = Lp − Lt. If Ci ≤ Ri, the time slice is enough toexecute its function task. Otherwise, the time slice is notenough to execute its function task. So the device sendsalarm messages to apply for resetting the time slices.101Figure 2. Execution of function.The third requirement can be solved using timer’sinterrupt. The programme sets a timer that triggers aninterrupt when communication time slice or function timeslice arrives. EPA-FBS method is realized in the interrupthandler of the timer. The interrupt handler is shown asFig. 3. When the interrupt is triggered, device i obtaincurrent time Lt to determine whether current time is in thecommunication time slice or not according to the followingequation:G =⎧⎨⎩Di ≤ MOD(Lt, T) ≺ Ds i = nDi ≤ MOD(Lt, T) ≺ Di+1 i = n(8)Therein, Di is the periodic-data-sending offsets of de-vice i, and Di+1 is the periodic-data-sending offsets ofdevice i+1. Ds is the non-periodic-data-sending offset ofthe network. G is a logical variable that indicates whethercurrent time is in the communication time slice or not.If G is true, current time is in the communication timeslice. The device calculates the start time of function timeslice and updates the timer then sets scheduling tags of allthe FBs in the device to true and then sends out periodicmessages. If G is false, current time is in the function timeslice. The device calculates the start time of communica-tion time slice and updates the timer and then scans andexecutes FBs.In addition, to ensure the transmission of non-periodicmessage, a timer for the transmission of non-periodic mes-sages is set. When the start time of the non-periodicmessages time slice arrives, the timer triggers an interruptand the interrupt handler calculates the start time of nextnon-periodic messages sending time slice and updates thetimer and then sends out non-periodic messages.Figure 3. Flow chart of interrupt handler of function tasktimer.Figure 4. Experiment platform.5. ExperimentIn this section, an experiment is conducted to verify theeffect of EPA-FBS method. As shown in Fig. 4, theexperimental platform is made up of a personal computer(PC), an EPA bridge and an EPA network, including aHUB, a TE (test equipment) and four DUTs (devices undertest). The DUTs and TE are EPA control modules. EPA-FBS method is realized in their protocol stack. The TE102Figure 5. Function diagram.Table 2Configuration of Communication Time Slice andAdjustment LimitDUT Di Sa Sb Ds Ba Bb T(ms) (ms) (ms) (ms) (ms) (ms) (ms)1 0 0.2 22 2 0.2 23 4 0.2 24 6 0.2 29 1 1 10TE 8 0.5 0.5Port 8.5 0.5 0.5runs a specific programme for monitoring and analysingmessage transmission in the network. EPA-FBS methodand EPA-timeslice self-adaptive adjustment (TSA) methodproposed in [20] are realized in the communication protocolstack in the DUTs and TE. The EPA Bridge is used toforward the messages between the network and the PC.The PC runs a configuration and analysis software toconfigure the system and process experimental data.As shown in Fig. 5, 20 FBs distributed in the 4DUTs are connected into 5 control loops. After applicationof EPA-FBS method, DUT1 sends two messages, DUT2sends one message, DUT3 sends three messages and DUT4sends one message in each macrocycle. The messages areEPA periodic messages whose sizes are 74 bytes. Beforethe application of EPA-FBS method, the execution timesof function task in each macrocycle depend on the scanningcycle of each DUT and the number of messages thateach DUT needs to send in each macrocycle depends onthe scanning times. By comparing the communicationtime slice between before and after application of EPA-FBS method, the effect of EPA-FBS method to reducecommunication load and execution times of FBs can beobtained.The initial values of the periodic-data-sending offsetsDi and the non-periodic-data-sending time slice Ds, theallowable extreme values Sa and Sb of communication timeslice, the allowable extreme values Ba and Bb and theFigure 6. Time slices comparison before and after applica-tion of EPA-FBS method.Figure 7. Network delays comparison of control loops be-fore and after application of EPA-FBS method.macrocycle T are shown in Table 2. The non-periodicmessages sending time slice, the communication time slicesof TE and testing port are locked so as to prevent the ex-perimental results from being disturbed. The TE obtainsthe communication time slices of all the DUTs and thenon-periodic messages sending time slice of the network ineach macrocycle by means of receiving and processing theNDA (non-periodic data annunciation) messages. ThenTE transmits the data to the configuration and analysissoftware in the PC through the EPA network. The config-uration and analysis software running in the PC receivesand processes the data and makes the average of the timeslices from 100 macrocycles to display.In Fig. 6, the communication time slices Si and thenon-periodic messages sending time slice B before and afterapplication of EPA-FBS method are shown. Before theapplication of EPA-FBS, the communication time slices arevery big. The communication time slices of the DUT1 andthe DUT3 reach their maximum: 2 mm. While after theapplication of EPA-FBS, the communication time slicesof DUT1–DUT4 reduce 67.6%, 61.2%, 61.8% and 65.4%,respectively, and the macrocycle reduces 48.8%. The morecommunication times a device need, the more obviousthe effect of the reducing communication time slice is. Thereduction of the communication time slices reflects thereduction of the communication load [20]. Combined withthe previous content, the experimental results show thatthe execution times of FBs are reduced. The reductionof the execution times of FBs means the reduction of thecalculation load of the EPA system so that the operationefficiency can be improved.Moreover, as shown in Fig. 7, after the applicationof EPA-FBS method, the network delays of control loop1031–control loop 5 reduce 46.2%, 44.9%, 43.1%, 43.1% and67.5%, respectively. Thus, the experiment shows thatEPA-FBS can improve the real-time performance of EPAsystem.6. ConclusionIn this article, a method to improve the real-time perfor-mance of EPA industrial Ethernet is proposed on the baseof EPA deterministic scheduling mechanism. The methodintegrates all the FBs in a single-field device into a functiontask and sets the function time slice for the execution ofthe function task according to the principle of the cyclesynchronization between the execution of FBs and the datacommunication in EPA system. On this basis, the methodfirst realizes the single execution of each device’s functiontask in an EPA macrocycle by setting a scheduling tag ineach FB and then realizes the quick trigger execution ofthe function task when its time slice arrives by using timerinterrupt. By the previous means, the method realizes thesynchronization between the execution scheduling of FBsand EPA deterministic communication so that it preventsthe invalid executions of FBs in EPA system. The ex-periment proves that the method reduces the communica-tion load and improves the real-time performance of EPAsystem.AcknowledgementThe work reported in this article was funded jointly by twoprojects, which are the project of national science and tech-nology supporting plan of China (No. 2015BAF20B02).References[1] I. Draganjac and T. Petrovic, Highly-scalable traffic man-agement of autonomous industrial transportation systems,Robotics and Computer-Integrated Manufacturing, 63(1), 2020,169–182.[2] D. Aslan and Y. Altintas, Prediction of cutting forces in five-axismilling using feed drive current measurements, IEEE/ASMETransactions on Mechatronics, 23(2), 2018, 833–844.[3] S. Kayalvizhi and D.M. Vinod Kumar, Planning of au-tonomous microgrid with energy storage using grid-basedmulti-objective harmony search algorithm, International Jour-nal of Power and Energy Systems, 37(1), 2017, 10–18. DOI:10.2316/Journal.203.2017.1.203-6276.[4] IEC/TR 61158-1, Digital data communication for measurementand control – Fieldbus for use in industrial control systems– Part 1: Overview and guidance (Geneva, Switzerland:International Electrotechnical Commission, 2007).[5] IEC61784-2, Industrial communication networks – Profiles –Part 2: Additional fieldbus profiles for real-time networksbased on ISO/IEC 8802-3 (Geneva, Switzerland: InternationalElectrotechnical Commission, 2007).[6] J. Wang, C. Xu, and W. Sun, Mine fully mechanized monitoringsystem of multiple fieldbus based on EPA standard, Coal MineMachinery, 37(12), 2016, 177–182.[7] H. Wang, G. Wu, and P. Wang, Application of DRP insmart substation based on EPA, Automation of Electric PowerSystems, 36(17), 2012, 77–81.[8] X. Zhu, Research on real-time Ethernet technique acceptablefor digital substations, Guangdong Electric Power, 24(10),2011, 48–52.[9] D. Mestriner and M. Invernizzi. Analysis of lightning ef-fects on power plant connection, International Journal ofPower and Energy Systems, 38(2), 2018, 40–49. DOI: 10.2316/Journal.203.2018.2.203-0011.[10] W. Wang, B. Yang, and C. Shi, Development of EPA elec-tric actuator based on small embedded RTOS, InstrumentTechnique and Sensor, 46(8), 2010, 22–29.[11] X. Wang, X. Hu, and Y. Zhang, Design and research oflow-voltage DC Servo with EPA, Computer Engineering andApplications, 46(19), 2010, 58–66.[12] H. Li, H. Zhang, and D. Peng, Design and application ofcommunication gateway of EPA and MODBUS on electricpower system, Energy Procedia, 02(17), 2012, 286–292.[13] Y. Cao, Y. Tong, and Y. Tang, Application of EPA real-timeEthernet technology in marine PLC control system, InstrumentStandardization & Metrology, 36(1), 2019, 18–21.[14] S. Luo and J. Huang, Design of integrated control system forbrake valve maintenance based on EPA protocol, TechnologyInnovation and Application, 12(5), 2018, 110–114.[15] Q. Tong and T. Wang, The EPA on-chip communication systemwith AMBA bus, China Instrumentation, 26(4), 2018, 65–70.[16] R. Shi, Research and implementation of PLC network com-munication function block technology (Dalian, China: DalianUniversity of Technology, 2016).[17] Y. He, D. Feng, and Y. Zhu, Deterministic transmission of mul-timedia data based on EPA network, Computer Engineering,40(2), 2014, 26–30.[18] F. Cheng, D. Feng, and J. Chu, Industrial wireless network real-time and reliable routing algorithm based on EPA, ComputerEngineering, 40(5), 2014, 73–80.[19] K. Tian, Research on security schemes under EPA standardsfor industrial control networks (Shenyang, China: ShenyangUniversity of Chemical Technology, 2019).[20] N. Liu, C. Zhong, and H. Teng, Self-adaptive adjustmentmethod of the data transmission time-slice in EPA sys-tem, Chinese Journal of Scientific Instrument, 30(11), 2009,2298–2304.[21] X. Liu, Delay features analysis of EPA real-time industrialEthernet based on µclinux, Information and Communications,13(3), 2016, 24–29.[22] N. Liu, K. Lv, and T. Xue, Synchronization method betweencontrol and communication in the system based on EPA real-time Ethernet, Control Engineering of China, 26(7), 2019,1391–1396.[23] N. Liu, C. Zhong, and T. Xue, A function blocks execut-ing method in the control systems based on real-time Eth-ernet, Computer Engineering and Applications, 55(13), 2019,112–118.

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