PROFINET is the abbreviation of the process field network and is an industrial Ethernet standard that was developed by Profibus & Profinet International for the automation industry as well as for the entire propulsion technology.
The technology of Profinet is based upon Ethernet/IP. It supplements existing PROFIBUS technologies. Fast data communication is a characteristic of Profinet.The concept of Profinet is modular, so that the user himself can decide the functionality. The differences then lie in the data transmission method, which is adapted to different speeds.
Decentralized Peripheral – Profinet IO
Profinet IO is a further development of the Profibus DP technology. Profinet IO describes the data exchange and/or the communication between the control unit and decentralized field devices. In this way, the producer-consumer model is used, which supports the communication between the equally ranked subscriber devices.
With this model, the provider sends its data without the direct request of a consumer, thus making it always available. These data always are transmitted through real-time communication, so that the data exchange only covers a few milliseconds. Parametrization and diagnosis also are part of Profinet IO technology.
Connection via External and Internal Switches
The Profinet IO field devices can be connected to the network via internal or external switches. The Fast Ethernet standard transmission on which the Profinet IO is based is 100 Mbps.
Some Profinet IO devices have internal switches, which makes a linear network structure possible without external connections. Because of the linear structure of the network, only point-to-point transmissions can be realized. In the case of faults in a device in the line, the connection is interrupted completely, as the data cannot be transferred any further. Accordingly, it is recommended to plan redundant communication paths during the configuration of the installation. In order to avoid this problem, this is supported by Profinet IO.
Device Classes
As Profinet IO uses the provider-consumer model for data transmission, any function arrangements may exist in a Profinet IO device. The following device classes result from this:
- IO Controller – Corresponds to a programmable logic controller (PLC). In connection with this, the automation program runs (comparable with the master).
- IO Supervisor – This corresponds to either to a programming device (PG), a personal computer (PC) or a human-machine interface device (HMI) which is n charge of maintenance or diagnosis.
- IO Device – This corresponds to a decentrally arranged IO device which is connected by Profinet IO (comparable to a slave).
In a Profinet network, there has to be at least one IO controller and several IO devices.
The IO supervisors in most cases operate only for a short time for start-up in the network.
Data Traffic
The data traffic can take place in four different ways in a Profinet network:
- Cyclic Data Traffic – I/O data are transmitted in a parametrizable grid between the IO controller and IO devices. This takes place in real-time communication. The IO controller also monitors the validity and the reception of the data.
- Acyclic Data Traffic – With this, IO devices can be parameterized and configured. This is possible as a result of the read-write frames. The services to be executed with the read-write frames can be specified.
- Lateral Data Traffic (MCR) – Multicast communication relation (MCR) is the term that describes data transmission from one provider to multiple consumers / all consumers.
- Event-controlled Data Traffic – Fast transmission of events through alarm signals. The source of these events can be system-defined or user-defined.
The Profinet IO Device Model
The Profinet IO field devices are divided into two types:
- Compact field devices – The degree of expansion cannot be changed.
- Modular field devices – The level of expansion can be changed and adapted depending on the area of application.
All field devices are specified with a GSD file (general station description). Here, for example, the DAP (device access point) is defined. This serves as a kind of access point for the communication. With Profinet IO, the device model was supplemented with a further nesting depth of the slots, the subslots.
The slots indicate the socket in a modular field device, the subslots are the actual connections to the processes. The index is used to read and write the data within the subslots. This occurs in the acyclic data flow via the read-write system and as such, data are specified more accurately.
The index is also responsible for the function which is to be provided in this process.
Operation Method of the Profinet IO
The Profinet network is configured by means of the GSD data, which are provided by the manufacturer. With this, the modules are assigned to the respective slots.
Each field device is now assigned a name (IP address) so that later the devices can be identified and differentiated more easily. This is done with the DCP protocol that is integrated into each field device.
The configuration data are transmitted to the IO controller.
The system is booted and the parameters are transmitted to the IO devices.
The communication paths must be built up to enable communication between the IO controller and an IO device with Profinet IO. Each data exchange is based on an application relation (AR) that determines the relation between the IO controller and the IO device. Within the AR, the data are specified more accurately through communication relations (CR). This means that certain channels are defined for data exchange. When the AR is set up, the communication channels, the alarms and the lateral traffic relations are set up at the same time.
The communication between the IO controller and the IO devices is built up by different frames, e.g. the connect frame. With this, all of the relevant data that are required for the build-up are transmitted. Among other things, this includes the data for parametrization. By indicating “application ready”, the IO controller signals that the first data exchange can now take place…