Overview Of PROFINET system redundancy
PROFINET system redundancy standard distinguishes between four configurations with the designation NAP S1,S2,R1 and R2.
NAP: Network Access Point means PN interface of Module. It is not the interface IO module but PROFINET Port on the module. If a module has 2 ports acting as a switch then it is counted as 1 NAP.
The S (Single) describes and IO device with one PN interface. An R (Redundant) indicates that the IO device has two NAPs:
- Either 2 interface module each with a PN interface or
- One interface module with two independent PN interface.
With NAP S2 and Rs, two IO controllers(IOCs) can be assigned to one NAP-a PN interface of an interface of an interface module. It should be noted here that the NAP in operation uses only one of the two connections actively for IO data exchange and switched to the other connection only if there is a failure.
Important Note:
With system redundancy, the IO controller (IOC) – in other words the PN interface of the PLC – and the interface module of the IO device must both support the corresponding PROFINET system redundancy function. It is not possible to redundantly connect an IO device that supports NAP S2, like the ET 200SP with a High Feature interface module, to two standard S7-1500 controllers, because this
type of PLC does not support NAP S2. This configuration would be limited to the smallest common configuration – in this case NAP S1 – and would permit connection of the ET 200SP to only one of the two controllers.
Application Relation means connection between IO controller and IO device. In 2 AR means one NAP (IO interface) can make connection with 2 IO controller, Only one AR can be active at one time.
PROFINET System Redundancy S1
NAP S1 describes an IO device with exactly one PROFINET interface. Taking the example of an ET 200SP or ET 200MP that would be an IO device with one interface module and with one PN interface.
Via its PN interface this interface module has a communication relationship (AR) to a controller (IOC), the PN interface X1 of an S7-1516F, for example.
In the case of failure (disconnection, PLC failure) the device cannot switch over to another communication connection. This is not a redundant configuration, but describes the actual PROFINET standard.
Remark:
PROFINET NAP S1 is supported by every standard IO device and is mentioned in the PROFINET system redundancy standard only for the sake of completeness. This does not affect the availability of a plant configuration.
When you connect a NAP S1 device to a redundant control system (S7-400H, for example), such an IO device can only be assigned to one of the two controllers (IOC). In the case of failure (failure of the corresponding PLC, for example), the remaining controller cannot take over this IO device even though the IO device and the PN interface of the controller are physically in the same network.
PROFINET System Redundancy S2
With a NAP S2 configuration, an IO device has exactly one PROFINET interface (NAP), in the case of an ET 200SP this corresponds to an interface module with one PN interface.
This one interface module can establish up to two communication relationships (ARs) with two IO controllers (IOCs) – exactly on AR per IOC. During operation, of these two connections one is used for the IO data exchange (primary AR) and the other is held in reserve (backup AR). In the PNO system redundancy standard one speaks of an AR set with two ARs.
If there is a fault with the primary AR, the control system switches to the backup connection. The data exchange then runs over the second configured IO controller (IOC).
PROFINET System Redundancy R1
NAP R1 describes an IO device with two PN interfaces. In the case of a SIMATIC IO station this would be one interface module with two PN interfaces or two interface modules each with one PN interface but the same IOs.
This configuration is primarily for designed for use on redundant networks like redundant lines or rings. However, this is not an absolute requirement because, according to the standard, both IOCs and both NAPs are also allowed to be in the same single network (line, ring, star).
Each of these two NAPs has a communication relationship (AR) to its own IO controller (IOC). According to this, compared to the NAP S2 the redundancy is achieved not through two communication relationships per interface but through doubling of the PN interfaces.
In this way a PN interface (NAP) cannot switch between the two IO controllers (IOCs) because it has only one communication relationship (AR) to one IO controller (IOC). Instead, in the case of failure of the active communication relationship (primary AR) there is switchover to the second available PN interface (NAP). As already with NAP S2 one speaks here in the PNO system redundancy standard of an AR set with two ARs.
PROFINET System Redundancy R2
The NAP R2 configuration combines the two solutions NAP R1 and S2 in that it
can process two PN interfaces (NAPs) per IO device and each of these interfaces
can process two communication relationships (ARs) to two IO controllers (IOCs).
Compared to NAP S2 and NAP R1, in this case access can be made to four
possible communication relationships, which is called an AR set of four ARs in the
PNO system redundancy standard.
Note: This is only for educational purpose. Please cross verify with experts before any implementation.
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