Wireless communication as an alternative to cable s has numerous advantages over wired systems and is the gold standard for flexible productions and modular plants. However, especially for applications with functional safety, some issues should be considered when selecting and installing the appropriate wireless solution in order to achieve stable and secure data communication. In an industrial context, PROFIsafe is often used as a bus protocol for such safety-critical applications. Read on to see how to achieve secure wireless communication and which specifics you should consider when using PROFIsafe in an industrial environment.
Whether for a crane control system, the emergency stop transmission of a production machine, or other safety-relevant communication: PROFIsafe has been established as a standard for functionally safe communication and has been an international standard since 2007 under the designation IEC 61784-3-3. The safety-related protocol is used to transmit data between a safety controller (F-PLC or F-Host) and field devices (F-Devices). While the controller and device are usually safety-related components and must be certified accordingly, PROFIsafe, according to the system description, has no effect on the standard bus protocols used: whether with Industrial Ethernet (PROFINET IO), via RS485 (PROFIBUS-DP), via backplanes or wireless – the method used for data transmission has no influence on the safety rating. The transmission channels are merely so-called "black channels", of which the actual PROFIsafe application is completely independent. Accordingly, the PROFIsafe system description also states: Wireless transmission is permissible as long as sufficient availability (no false alarms) and IT security are guaranteed.
This means that the use of wireless technologies is also provided for and possible by definition, just like other radio technologies. Both the safety controller and the remote IO system – for example a safety switch – contain the safety protocol. The interface between them is merely the channel for transmitting the safety information. Accordingly, no safety certification is required for the wireless device and it is treated like other infrastructure components, such as switches or cables. This makes the recalculation or verification of the safety level (SISTEMA) for using a black channel solution obsolete.
Data transmission for PROFIsafe can be used as a transmission standard independent of the protocol used for data transmission – e.g. for any wireless technology such as WiFi, Bluetooth, and, in the future, 5G. Factors such as data transmission rate and error detection do not play a role. To ensure wireless functional safety, PROFIsafe uses a number of measures that are integrated into the protocol: For example, F-messages are numbered; the receiver can thus check whether messages have been received completely and without sequence errors. Timeouts, until a message is acknowledged, are detected and a unique authentication of sender and receiver ensures that no manipulation of the communication is possible. PROFIsafe also uses a cyclic block check for data integrity.
With these comprehensive mechanisms, PROFIsafe applications can meet safety parameters up to SIL3 according to IEC 61508 or Performance Level e (PLe) according to EN ISO 13849-1.7
In principle, therefore, the procedure for using a PROFIsafe application – whether with a cable or wireless – does not differ. Nevertheless, there are some points and essential differences that should be taken into account for secure wireless communication in an industrial environment: Compared to data transmission via cable, the lower transmission rate and fluctuating latency times must be taken into account when using a wireless solution. If the standard update interval of 1 ms is used here, as is usually the case with wired PROFINET communication, radio links would quickly become overloaded. As a result, lost telegrams occur, which ultimately lead to bus errors and thus a shutdown and standstill of the system.
To compensate for the lower data rates and fluctuating latencies, it is possible to extend the update time. However, this has the effect of slowing down the entire application - this is often problematic for safety-related functions of a system or machine. For crane controls, for example, the maximum monitoring time must not exceed 500 ms.
A system standstill due to a bus error often costs a lot of time for restarting the system – and thus a lot of money for the operator. Therefore, it is important to already consider the risk of such errors when selecting the components for functional safety via wireless networks. The patented DATAEAGLE technology for secure wireless communication in industrial environments is particularly suitable for this. It was specially developed by Schildknecht and compensates for the lower data rate and fluctuating latency of radio communication compared to cable solutions. To do this, DATAEAGLE relies on pre-processing of the telegrams. It filters the information and does not transmit redundant information. This reduces the amount of data so that the controller can transmit with the fastest possible update time of 1 ms despite radio transmission. The transmission interval is flexibly adapted to the radio connection. If only a part of the data changes, then only this part is transmitted. In this way, DATAEAGLE ensures stabilisation of the PROFIsafe data transmission with a simultaneously high update speed. The solution is optimal for creating reliable and stable automation solutions with radio data transmission.
PROFIsafe can be implemented with radio solutions – with the black channel principle, data transmission has no influence on the safety rating.
When selecting the appropriate wireless solution, the lower data rate and fluctuating latency of wireless compared to cable should be taken into account.
Radio transmissions with pre-processed data packets, such as DATAEAGLE from Schildknecht, are ideally suited. This method reduces the amount of data and increases stability.
Safety-critical applications can be realised with PROFIsafe and radio data transmission – and have proven themselves in industrial environments, in some cases over many years of operation and without interruption due to bus errors.
Intelligent radio data transmission systems with stabilised radio transmission are characterised by reliability and long service life without maintenance by secure communication and robustness against interference. This makes them ideal for use in automation technology. The patented DATAEAGLE product family also offers maximum flexibility and uncomplicated plug & play installation. This way, you can achieve the optimal solution for wireless data transmission in the shortest possible time.
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