Product Overview

PROFINET Topology

PROFINET Topology for Flexibility in the Network

PROFINET has been established an open Industrial Ethernet standard. Aside from the set up of a simple PROFINET topology the combination of PROFINET and PROFIBUS components is possible as well. This is an advantage regarding extension and power increase of an already present PROFIBUS installation. PROFINET devices can, if appropriately designed, easily be exchanged and addressed which decreases the effort required when changing the network. Within the PROFINET standard, classic line topologies as well as ring, star and tree topologies are permitted. PROFINET is specified in the IEC 61158 and IEC 61784 standard.

PROFINET CBA and PROFINET IO

Regarding information about PROFINET, a distinction has to be made between PROFINET CBA and PROFINET IO. Two different Approaches are used with the two PROFINET variations. PROFINET CBA (Component based Automation) was specified in 2001 and is based on Splitting up the automation task to multiple sufficiently intelligent devices. PROFINET IO is now commonly used. PROFINET IO depicts communication between a central control unit and decentralized field devices in a provider-consumer-model. In 2020 PROFIBUS and PROFINET International (PI) counted 32.4 million PROFINET knots worldwide. PROFINET IO is the leading standard for Industrial Ethernet Networks and this position is established even further.

Device Classes in the PROFINET Topology

The PROFINET standard distinguishes between three device classes. A SPS which is used to control the automation task within a PROFINET topology is called IO Controller. The IP network of a PROFINET topology may include multiple IO Controllers. The included field devices are described as IO Device and communicate in accordance with the IO topology with the assigned IO controller. The third device class IO Supervisor includes engineering tools for parametrization and diagnosis of the IO Devices. Programming, parametrization and diagnosis require a screen and an input device like a keyboard, mouse, touchpad and touchscreen for the user. Mobile as well as fixed devices like PC, Laptop, programming device and HMI system (Human-Machine-Interface) can be used.

IO-Device - managed Switch with 6 ports. Installation in the control cabinet (IP20).

Data Traffic - Cyclic and Acyclic

PROFINET differentiates between the types of data traffic for communication between network participants. The basis for communication between IO Controller and IO devices is I/O Data and status information which is exchanged in adjustable distances. This type of communication is described as cyclic data traffic. It can cause a high load on the network. Data cross traffic can be used to reduce the load on the network. Acyclic only occasionally occurring data transfer is used for configuration, parametrization, and diagnosis. A special form of communication is data traffic triggered by events which implements the alert concept of the standard. Alert messages have to be transmitted fast, with high priority and with provision of required storage space into the network knot to ensure safe action regarding the event.

Planning of the PROFINET Topology

The planning of the automation project is realized in multiple steps. A detailed description can be found in the planning guideline of the PROFIBUS user organization. Structured planning simplifies later changes or extensions to the network and secures investment security. It creates a solid basis to decide early on the use of high quality components such as managed switches which allow to customize the network in regards to a higher availability.

Set-up PROFINET - Topology Basic Shapes

Once the components such as IO Controller and IO devices of the plant have been determined in the previous step the planning of the PROFINET topology can be initiated. PROFINET supports line, tree, ring and star topologies. During installation they may be combined into a complex network structure. Each of this basic shapes has its advantages and disadvantages which have to be taken into account during the process of planning the PROFINET topology.

Manufacturing plants are highly individualized depending on the product being manufactured. Machines and handling equipment in different sizes have to be fitted into a limited space. This creates a high number of different designs which have to be connected to the network. By supporting basic topologies like star, tree, line and ring, PROFINET provides the possibility choose the adequate layout for any circumstance.

IO-Device - managed Switch with 5 Ports. Installation in the Field (IP67).

Line Topology

The layout of a line topology is perfectly suited for big factories in which machines are set up in a line. The knots of a line topology are connected in a line like layout. They form an order of points through which the signal is transmitted. PROFINET switches (external switches) should be used for the knots. They transmit the signal to the next part of the line topology and can be connected to a PROFINET field device. If the connected PROFINET field device has an integrated switch, the external switch is not required. The number of components in the network is reduced and the effort necessary for installation and maintenance is decreased. This advantage should be taken into account during the process of evaluation. Decreased effort required for wiring is an additional advantage of the line topology. The overall length of cables in a star topology is much higher due to longer distances between the knots than in a line topology.

Ring Topology

A ring topology is realized through a simple connection of the end point with the higher level network knot. The standardized PROFINET topology allows the set-up of a ring redundancy which increases the availability in contrast to a line topologyy. The redundancy support requires the use of managed switches. This has to be taken into account during the selection of the PROFINET components. Ring topologies may also be configured in a tree topology to create a highly available system. Each hub with a switch is assigned to an additional knot which has an as redundancy manager configured managed switch. It is connected with a separate redundant line.

Star Topology

A star topology is set up by multiple PROFINET devices which are connected to a central switch which is the connection to the higher level network segment. The number of PROFINET devices which can be connected is limited by the number of free ports on the switch. A star topology presents an advantage for large designs with many participants since it decreases the line depth in contrast to a line topology.

Tree Topology

The tree topology allows to portray functional relations between parts of a plant. Structuring machines and plants into production islands is a proven measure for the design of a manufacturing facility. By using a tree structure which is realized through a chain of PROFINET switches with subordinate star topologies, the selective production islands can be realized in the physical structure of the network. Another important advantage is that segments of the tree topology can be easily extended. PROFINET splits the flow of messages according to the addressing.

Messages are only transmitted to the subordinate star knot in the tree if the addressed PROFINET device is within that specific segment.

Requirements for a PROFINET Topology

A number of requirements have to be met to ensure a smooth operation and required data quality for a network run by PROFINET.

Spacial Arrangement of PROFINET Devices

The arrangement of network components in the manufacturing facility depends on the local conditions. Routes have to be bypassed. To protect sensitive components a sufficient distance to machines and workpieces with high temperatures is mandatory. As long as power supply via PoE (Power over Ethernet) is impossible, the distance to the power supply is another criterion.

Highly resistant PROFINET components such as I/O modules with a metal case enable the extension of the network into manufacturing areas which present high stress on network components through weld splatters and aggressive media.

Picture MVK PROFINET Compact Module, Metal Case

The process of planning includes checking the depth of the line which is the number of switches in between an IO Controller and the respective IO device. Each switch delays data transmission through its internal processes. A high line depth may lead to unacceptable transmission times from the IO device to the IO controller.

Establish a Primary Route of Communication

The planning guideline of PI (PROFIBUS & PROFINET International) recommends to establish a primary route of communication which carries the main load of the PROFINET communication. Managed switches equipped with a PROFINET certificate should be used on the primary route of communication.

The establishment of a primary route of communication serving as central part of the entire network with powerful switches simplifies and secures the long term and simple connection of additional network segments. Managed Switches can transmit diagnosis information via OpenVPN. The ability to transmit diagnosis information via the primary communication route allows future extension of the network infrastructure even if diagnosis is not part of the initial intent.

Flexibility and Investment Security through Multi-Protocol Components

In addition to PROFINET, EtherNet/IP has become one of the most important Industrial Ethernet protocols. Flexibility for the use of a number of different Networks is ensured through components such as I/O modules which support PROFINET as well as EtherNet/IP. If a future change to another network protocol can not be fully excluded the investment can be secured by the use of multi-protocol components.

Picture I/O Module SOLID67 IOL8 60mm M12L 5P

PROFINET Topology und IO-Link

The simple connection of IO link devices to the PROFINET can be realized by using distributors which support both standards.

Picture PROFINET, Compact Module, IO-Link

Distance and Length of Lines

The maximum transmission length of the chosen transmission technology has to be taken into account when selecting the topology for the PROFINET based network as well as for individual segments. For copper cables with a maximum of four connections it is 100 m (PROFINET-End-to-End-Link). The connectors include plug in connectors to devices inside and outside of the control cabinet and couplings (e.g.: plug-socket connections in power outlets for wall feed through of network cables).

Picture RJ45 Heavy Duty Plug 90° top 8pol. PROFINET

A calculation for the permitted length per line for different channel classes (Class D, Class E, Class F) can be found in ISO/IEC 11801 Table 21.The length of patch cables lowers the available length of the installation cable. Fiber optic cables allow a much longer transmission length. Depending on the planned installation and the length of the route higher cost for fiber optic cables is to be evaluated.

During budget Evaluation for the network infrastructure savings through higher capability of PROFINET components have to be included. If e.g. engines have to be connected to the control unit via the network this lowers the effort for control cabinets.

Picture Cube67+ E/A Extension Module MOVIMOT

PROFINET Topology and EMV

Lowering the cost of the network infrastructure and improving the utilization of available cable ducts is achieved through joint routing of energy and data lines. If the PROFINET lines are made from copper the advice from the PROFINET installation guideline of the PI in regards joint routing with energy lines has to be implemented.

Separating Potentials in the PROFINET Topology

High potential differences in parts of the network may cause interfering compensation currents via the ground of the copper cable shielding. Therefore effective measures for potential separation are part of careful evaluation. The PROFINET topology may include parts with fiber optic cables which offer the required potential separation.

The connection of I/O devices via I/O modules with galvanic separation protects the network of unwanted influences.

Picture MVK PROFINET Compact Module, Metal, galvanic Separation

Conformance Classes in the PROFINET-Topology

PROFINET devices are classified into four conformance classes (Conformance Classes CC-A, CC-B, CC-C and CC-D). The goal is to structure the whole range of functions and secure that the PROFINET device is able to fulfill the specific task within the network for which it was selected. The classes are based on one another and define a range of functions, from communication to transmission, synchronization and availability.

Safety functions with PROFIsafe in the PROFINET-Topology

PROFINET permits the integration of network segments with safety relevant tasks. PROFIsafe allows to integrate devices and network segments for safety tasks such as an emergency stop. Communication in the PROFINET topology with PROFIsafe may include security functions up to security level 3 (SIL3).

Picture MVK PROFINET/PROFIsafe compact module, metal

PROFINET-Topology for high Availability

Due to inside or outside influences some network components may fail. If the failing component is a switch of a star or a tree topology, the worst case is failure of communication to the subordinate knots and network segments. If high availability is required in a production plant measures to create sufficient redundancies which are supported by PROFINET should be taken. Once alternative routes for communication are implemented into a network or a network segment, the fail-safe security of the network increases.

PROFINET supports the concept of redundancy. Redundant communication lines may be integrated to ensure availability of all parts of a plant even if a switch (external or integrated) fails. Redundant lines should not be run through the same cable routings to rule out a simultaneous fail of both lines. Requirements for the exchange of broken network participants determine whether external or integrated switches should be used.

Network Load and Performance in the PROFINET Topology

The performance of the system is determined by the network load created by the PROFINET participants. Consideration of the performance of a PROFINET based network is of high importance during the phase of planning. Refreshing time and the number of connected PROFINET participants are important factors for the network load. The refreshing time is the period of time during which the PROFINET device sends its data. The shorter the gap in between, the more up to date the data is. On the other hand it also increases the network load. The refreshing time of PROFINET devices can be set individually and may differ for each device.

Fitting and compatible M12 plugs and RJ45 plugs can be found here