Software program Redundancy in Siemens PLC – Hardware versus Software

 

Software program Redundancy in Siemens PLC – Hardware versus Software

After we've got mentioned the which means and significance of redundancy in Automation systems, nowadays we are going to have an overview of SIEMENS redundant solutions.

SIEMENS is one of the most essential main groups inside the Automation subject, it is recognised for its bendy software program (TIA portal) and its reliable Hardware components (PLCs – Circuit Breakers – HMI – …).

Table of contentsDifference Between Hardware & Software RedundancyHardware Redundancy in PLCSoftware Redundancy in PLCRequirements for Software RedundancyHardware RequirementsSoftware necessities“Software Redundancy” How Does It Work?Step 1: The Redundant SoftwareStep

2: The grasp station constantly transfers up to date information to the standby stationStep

3: Areas of the redundant software componentStep

4: Processing unilateral I/O devicesStep

5: Data trade among the two stationsStep

6: Master to standby changeoverStep

7: Recovering software redundancy after repairsRedundant programmable logic controllers from Siemens have proved themselves in operation and lots are in provider.Difference Between Hardware & Software RedundancyFirst of all, and earlier than we get into SIEMENS redundancy solutions, we had to differentiate between those two sorts of redundancy:Hardware Redundancy in PLCHardware Redundancy is a PLC model that you could see in (S7-400H & S7-1500H), it is used in essential strategies such as power plant life, gas manufacturing flowers, and high-velocity rotary equipment.In case of master CPU failure, the standby CPU can take control in 10ms order with preceding updates from the process. (In this way, the changeover is bumpless).Software Redundancy in PLCSoftware Redundancy can use any sort of S7-three hundred and S7-four hundred trendy CPUs, the redundant hyperlink among the CPUs may be implemented in widespread verbal exchange links over MPI, Profibus-DP, or Industrial Ethernet, and the switchover time (when a fault at the number one CPU will reason the standby CPU to take over the process) is measured in seconds.In popular terms, this will be defined as a heat-backup device: especially reasonably-priced, most of the programming for the redundancy ought to be completed by means of your self, and redundant IOs are limited. @ Read More greenitc1403 robotstechnologyies 

So, as we will note the primary benefit of hardware redundancy over software program redundancy is the “response rate”, Hardware structures have a quicker response/switchover time.Requirements for Software RedundancyHardware RequirementsTwo S7-three hundred and/or S7-400 stations each one geared up with a CPU and a connection for a DP grasp gadget. The  stations are related by way of a bus machine that you can use to change records.ET 200M dispensed I/O gadgets with redundant DP slave interface module IM 153-2 are related to DP grasp systems.The DP slave interface module allows the failover from the first to the second interface inside the occasion of a fault with a purpose to ahead procedure fame records from the second DP grasp to the I/O.

Software requirementsWe need to put in the STEP 7 Basic Package V5.2 or better to assign parameters to the blocks for software program redundancy.“Software Redundancy” How Does It Work?Before expertise the software redundancy algorithm, you have to learn similarly detail about the PLC experiment cycle and how does a everyday PLC work?This article (experiment cycle article) might help you to apprehend How a PLC executes a normal scan cycle.Step 1: The Redundant SoftwareFirst of all, you need to download the fault-tolerant thing of the software on both PLCs (the grasp and the standby stations).While the master CPU is processing the redundant consumer application, it's far skipped in the standby CPU.As the standby CPU skips this component of the program that would help to prevent inconsistency of the two program components, e.G. As a result of alarms, extraordinary cycle instances, and so forth.This approach that the program at the standby station is always equipped to take over-processing.

Step 2: The master station continuously transfers up to date records to the standby stationTo avoid having to begin the redundant consumer software “from scratch” after the failure of the grasp station, the master station constantly transfers its real technique statistics to the standby station.A grasp to standby station changeover is initiated immediately after a fault has been detected at a CPU, at a DP grasp, or at a DP slave within the master station.

With this kind of changeover, the standby station takes over the technique and assumes the master function.Step three: Areas of the redundant software program componentThe redundant software component includes a process photo, an IEC timer area, an IEC counter region, a bit memory address vicinity, and a information block region.

Only the redundant software is permitted write get right of entry to to those areas.Those contiguous areas are scanned during the venture of parameters for the “SWR_START” startup block (OB100).Step four: Processing unilateral I/O devicesThe time period unilateral I/O gadgets denote I/O modules that aren't addressed inside the redundant issue of the user application, i.E. They are best assigned to one CPU.In addition to the redundant software issue, it is, of route, additionally viable to load a program that controls the unilateral I/O devices of the relevant CPU.Software redundancy does no longer have any have an impact on on that element of the program.Step 5: Data alternate among the 2 stationsThe non-redundant thing of the program can change its facts with the redundant software program through suitable information blocks.Those facts blocks are exchanged through the software redundancy device and are therefore made available to the companion station.The inputs are written to the system photograph of inputs (PII) at the begin of OB 1.The redundant software program is processed earlier than any records of the redundant software issue (PIO, bit recollections, DBs, timers/counters, and instance DBs) is transferred to the standby system.The standby station ought to receive the facts from the active station after having finished its startup, or after redundancy has been recovered in that software factor.At the give up of OB 1, the facts of the redundant PIO is written to the manner photograph of outputs on the master and standby stations and is transferred from there to the I/O devices on the give up of the OB cycle.NOTE:

Interrupts may be obtained through the energetic station at any time and are processed at once.Interrupts can be misplaced if a changeover takes place at that second or rapidly later on.Step 6: Master to standby changeoverIn order to avoid having to begin the standby station “from scratch” after master failure, a entire and steady PIO of the fault-tolerant application component is transferred to the standby station to cover emergency/changeover situations.The time required for the switch might also take longer than one cycle, depending on the communique mode and the quantity of records to be transferred.

The DP slave stations failover robotically, as an instance after detection of a trouble on the DP master or on the DP bus of the DP master station.During this DP slave changeover, the most these days output PIO values are frozen on the DP slaves.Step 7: Recovering software program redundancy after repairsTo recover software program redundancy, as an example after the failure of a CPU, all configuration information and the entire software need to be loaded from the programming tool or memory card to the alternative CPU. That CPU is then began.ResourcesSIMATIC S7-300/S7-400 Software redundancy for SIMATIC S7.If you favored this article, then please enroll in our YouTube Channel for Instrumentation, Electrical, PLC, and SCADA video tutorials.You can also comply with us on Facebook and Twitter to receive every day updates.Read Next:Cloud-Based SCADAControlLogix ArchitectureAllen Bradley Powerflex VFDSTL Language in Siemens PLCVFD Commissioning ProcedureYou've efficaciously subscribed !

Table of contents

Redundant programmable logic controllers from Siemens have proved themselves in operation and heaps are in service.

Difference Between Hardware & Software Redundancy

First of all, and earlier than we get into SIEMENS redundancy solutions, we had to distinguish between those two varieties of redundancy:Hardware Redundancy in PLCHardware Redundancy is a PLC model that you may see in (S7-400H & S7-1500H), it's far used in essential techniques inclusive of power vegetation, gas production flowers, and excessive-speed rotary machinery.In case of master CPU failure, the standby CPU can take control in 10ms order with preceding updates from the system.

(In this way, the changeover is bumpless).Software Redundancy in PLCSoftware Redundancy can use any form of S7-three hundred and S7-400 standard CPUs, the redundant hyperlink between the CPUs may be implemented in general communique hyperlinks over MPI, Profibus-DP, or Industrial Ethernet, and the switchover time (whilst a fault at the number one CPU will purpose the standby CPU to take over the process) is measured in seconds.In standard phrases, this will be defined as a warm-backup machine: incredibly reasonably-priced, maximum of the programming for the redundancy ought to be carried out via your self, and redundant IOs are constrained.So, as we are able to note the main gain of hardware redundancy over software program redundancy is the “response fee”, Hardware structures have a quicker response/switchover time.Requirements for Software RedundancyHardware RequirementsTwo S7-300 and/or S7-four hundred stations each one ready with a CPU and a fitting together for a DP master gadget. The two stations are connected by a bus machine that you can use to trade statistics.ET 200M disbursed I/O devices with redundant DP slave interface module IM 153-2 are related to DP grasp structures.The DP slave interface module permits the failover from the primary to the second interface within the occasion of a fault on the way to forward process status information from the second one DP grasp to the I/O.

Software requirementsWe want to put in the STEP 7 Basic Package V5.2 or higher to assign parameters to the blocks for software redundancy.“Software Redundancy” How Does It Work?Before understanding the software redundancy set of rules, you need to learn similarly detail approximately the PLC scan cycle and the way does a regular PLC work?This article (experiment cycle article) would assist you to understand How a PLC executes a normal experiment cycle.Step 1: The Redundant SoftwareFirst of all, you have to down load the fault-tolerant aspect of the software on each PLCs (the master and the standby stations).While the master CPU is processing the redundant user application, it's far skipped inside the standby CPU.As the standby CPU skips this element of this system that might assist to save you inconsistency of the 2 software additives, e.G. Due to alarms, extraordinary cycle instances, and so forth.This means that the program on the standby station is continually geared up to take over-processing.Step 2: The master station continuously transfers up to date data to the standby stationTo avoid having to begin the redundant user application “from scratch” after the failure of the master station, the master station continuously transfers its actual process information to the standby station.A master to standby station changeover is initiated at once after a fault has been detected at a CPU, at a DP master, or at a DP slave within the master station. With this type of changeover, the standby station takes over the procedure and assumes the grasp feature.Step three: Areas of the redundant software program componentThe redundant software element consists of a process photo, an IEC timer region, an IEC counter vicinity, a bit reminiscence cope with vicinity, and a statistics block location.Only the redundant software is allowed write get admission to to the ones regions.Those contiguous regions are scanned at some point of the mission of parameters for the “SWR_START” startup block (OB100).Step 4: Processing unilateral I/O devicesThe time period unilateral I/O gadgets denote I/O modules that aren't addressed within the redundant issue of the consumer application, i.E. They're only assigned to at least one CPU.In addition to the redundant software program aspect, it's miles, of course, additionally feasible to load a application that controls the unilateral I/O gadgets of the applicable CPU.Software redundancy does now not have any have an impact on on that aspect of the program.Step five: Data alternate between the two stationsThe non-redundant aspect of the program can alternate its records with the redundant software program with the aid of appropriate information blocks.Those facts blocks are exchanged by using the software program redundancy machine and are consequently made available to the partner station.The inputs are written to the system photo of inputs (PII) on the start of OB

1.The redundant software program is processed earlier than any records of the redundant software program factor (PIO, bit reminiscences, DBs, timers/counters, and example DBs) is transferred to the standby device.The standby station have to acquire the facts from the active station after having completed its startup, or after redundancy has been recovered in that software program factor.At the end of OB

1, the facts of the redundant PIO is written to the system photo of outputs at the grasp and standby stations and is transferred from there to the I/O gadgets at the end of the OB cycle.NOTE:Interrupts can be acquired by the active station at any time and are processed right away.Interrupts may be misplaced if a changeover takes location at that moment or rapidly later on.Step 6: Master to standby changeoverIn order to keep away from having to begin the standby station “from scratch” after grasp failure, a entire and regular PIO of the fault-tolerant program thing is transferred to the standby station to cover emergency/changeover conditions.The time required for the transfer can also take longer than one cycle, relying at the communication mode and the extent of records to be transferred.The DP slave stations failover routinely, as an example after detection of a problem on the DP master or at the DP bus of the DP grasp station.During this DP slave changeover, the most currently output PIO values are frozen at the DP slaves.Step

7: Recovering software redundancy after repairsTo recover software redundancy, as an example after the failure of a CPU, all configuration information and the whole program must be loaded from the programming device or reminiscence card to the replacement CPU. That CPU is then started.ResourcesSIMATIC S7-300/S7-400 Software redundancy for SIMATIC S7.If you appreciated this text, then please join our YouTube Channel for Instrumentation, Electrical, PLC, and SCADA video tutorials.You also can comply with us on Facebook and Twitter to get hold of every day updates.Read Next:Cloud-Based SCADAControlLogix ArchitectureAllen Bradley Powerflex VFDSTL Language in Siemens PLCVFD Commissioning ProcedureYou've correctly subscribed ! @ Read More modernfashdesigner thetechcertified