Profinet

Profinet is an industry technical standard for data communication over Industrial Ethernet, designed for collecting data from, and controlling equipment in industrial systems, with a particular strength in delivering data under tight time constraints. The standard is maintained and supported by, an umbrella organization headquartered in Karlsruhe, Germany.

Functionalities

Overview

Profinet implements the interfacing to peripherals. It defines the communication with field connected peripheral devices. Its basis is a cascading real-time concept. Profinet defines the entire data exchange between controllers and the devices, as well as parameter setting and diagnosis. IO-Controllers are typically a PLC, DCS, or IPC; whereas IO-Devices can be varied: I/O blocks, drives, sensors, or actuators. The Profinet protocol is designed for the fast data exchange between Ethernet-based field devices and follows the provider-consumer model. Field devices in a subordinate Profibus line can be integrated in the Profinet system seamlessly via an IO-Proxy.

Conformance Classes (CC)

Applications with Profinet can be divided according to the international standard IEC 61784-2 into four conformance classes:

In Conformance Class A , only the devices are certified. A manufacturer certificate is sufficient for the network infrastructure. This is why structured cabling or a wireless local area network for mobile subscribers can also be used. Typical applications can be found in infrastructure or in building automation.
Conformance Class B stipulates that the network infrastructure also includes certified products and is structured according to the guidelines of Profinet. Shielded cables increase robustness and switches with management functions facilitate network diagnostics and allow the network topology to be captured as desired for controlling a production line or machine. Process automation requires increased availability, which can be achieved through media and system redundancy. For a device to adhere to Conformance Class B, it must communicate successfully via Profinet, have two ports, and support SNMP.
With Conformance Class C , positioning systems can be implemented with additional bandwidth reservation and application synchronization. Conformance Class C devices additionally communicate via Profinet IRT.
For Conformance Class D , Profinet is used via Time-Sensitive Networking. The same functions can be achieved as with CC-C. In contrast to CC-A and CC-B, the complete communication between controller and device takes place on Ethernet layer 2. The Remote Service Interface was introduced for this purpose.

Functionality	Class A	Class B	Class C	Class D
Basic functionality	RT-Communication Cyclic I/O Parameter Alarms	RT-Communication Cyclic I/O Parameter Alarms Network diagnostics Topology detection System redundancy	RT-Communication Cyclic I/O Parameter Alarms Network diagnostics Topology detection Bandwidth reservation Synchronisation Seamless media redundancy	RT-Communication Cyclic I/O Parameter Alarms Network diagnostics Topology detection Bandwidth reservation Synchronisation System redundancy Seamless media redundancy
Certification	Controller Devices	Controller Devices Network components	Controller Devices Network components	Controller Devices Network components
Cabling	IEC 61784-5-3 and IEC 24702: Copper Fibre optics Wireless	IEC 61784-5-3: Copper Fibre optics	IEC 61784-5-3: Copper Fibre optics	IEC 61784-5-3: Copper Fibre optics
Typical application	Infrastructure facilities Building automation	Factory automation Process automation	Motion control	Universal

Device types

A Profinet system consists of the following devices:

The IO-Controller, which controls the automation task.
The IO-Device, which is a field device, monitored and controlled by an IO-Controller. An IO-Device may consist of several modules and sub-modules.
The IO-Supervisor is software typically based on a PC for setting parameters and diagnosing individual IO-Devices.
System structure

A minimal Profinet IO-System consists of at least one IO-Controller that controls one or more IO-Devices. In addition, one or more IO-Supervisors can optionally be switched on temporarily for the engineering of the IO-Devices if required.
If two IO-Systems are in the same IP network, the IO-Controllers can also share an input signal as shared input, in which they have read access to the same submodule in an IO-Device. This simplifies the combination of a PLC with a separate safety controller or motion control. Likewise, an entire IO-Device can be shared as a shared device, in which individual submodules of an IO-Device are assigned to different IO-Controllers.
Each automation device with an Ethernet interface can simultaneously fulfill the functionality of an IO-Controller and an IO-Device. If a controller for a partner controller acts as an IO-Device and simultaneously controls its periphery as an IO-Controller, the tasks between controllers can be coordinated without additional devices.

Relations

An Application Relation is established between an IO-Controller and an IO-Device. These ARs are used to define Communication Relations with different characteristics for the transfer of parameters, cyclic exchange of data and handling of alarms.

Engineering

The project engineering of an IO system is nearly identical to the Profibus in terms of "look and feel":

The properties of an IO-Device are described by the device manufacturer in a GSD file. The language used for this is GSDML - an XML-based language. The GSD file serves an engineering environment as a basis for planning the configuration of a Profinet IO system.
All Profinet field devices determine their neighbors. This means that field devices can be exchanged in the event of a fault without additional tools and prior knowledge. By reading out this information, the plant topology can be displayed graphically for better clarity.
The engineering can be supported by tools such as PROFINET Commander or PRONETA.
Dependability

Profinet is also increasingly being used in critical applications. There is always a risk that the required functions cannot be fulfilled. This risk can be reduced by specific measures as identified by a dependability analyses. The following objectives are in the foreground:

Safety: Ensuring functional safety. The system should go into a safe state in the event of a fault.
Availability: Increasing the availability. In the event of a fault, the system should still be able to perform the minimum required function.
Security: Information security is to ensure the integrity of the system.

These goals can interfere with or complement each other.

Functional safety: Profisafe

Profisafe defines how safety-related devices communicate with safety controllers via Profinet in such a safe way that they can be used in safety-related automation tasks up to Safety Integrity Level 3 according to IEC 61508, Performance Level "e" according to ISO 13849, or Category 4 according to EN 954-1.
Profisafe implements safe communication via a profile, i.e. via a special format of the user data and a special protocol. It is designed as a separate layer on top of the fieldbus application layer to reduce the probability of data transmission errors. The Profisafe messages use standard fieldbus cables and messages. They do not depend on error detection mechanisms of underlying transmission channels, and thus supports securing of whole communication paths, including backplanes inside controllers or remote I/O. The Profisafe protocol uses error and failure detection mechanisms such as:

Consecutive numbering
Timeout monitoring
Source/destination authentication
Cyclic redundancy checking

and is defined in the IEC 61784-3-3 standard.

Increased availability

is one of the most important requirements in industrial automation, both in factory and process automation. The availability of an automation system can be increased by adding redundancy for critical elements. A distinction can be made between system and media redundancy.

System redundancy

System redundancy can also be implemented with Profinet to increase availability. In this case, two IO-Controllers that control the same IO-Device are configured. The active IO-Controller marks its output data as primary. Output data that is not marked is ignored by an IO-Device in a redundant IO-System. In the event of an error, the second IO-Controller can therefore take control of all IO-Devices without interruption by marking its output data as primary. How the two IO-Controllers synchronize their tasks is not defined in Profinet and is implemented differently by the various manufacturers offering redundant control systems.

Media redundancy

Profinet offers two media redundancy solutions. The Media Redundancy Protocol allows the creation of a protocol-independent ring topology with a switching time of less than 50 ms. This is often sufficient for standard real-time communication with Profinet. To switch over the redundancy in the event of an error without time delay, the "Media Redundancy for Planned Duplication" must be used as a seamless media redundancy concept. In the MRPD, the cyclic real-time data is transmitted in both directions in the ring-shaped topology. A time stamp in the data packet allows the receiver to remove the redundant duplicates.