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Wireless communication is ready for safety-related machinery applications

  • Published 25/02/2007
  • Last updated 20/05/2011

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Validation of safety-related wireless machine control systems
Wireless technologies have been used for several decades for remote control, but safety-related machine-to-machine applications are still rare. One reason is that message errors and malicious attacks are more probable in wireless communication than in field buses. The wireless communication can be compared to field buses, since they both offer quick throughput via a single channel. The communication is realised by using serial mode communication, i.e. bits are sent one after another. 

Now, the price of electronics is going down in comparison with cables. Therefore technologies minimising the amount of the cables are getting more common. Wireless communication offers also some other benefits like freedom of moving devices and easy assembly. This means that in certain applications wireless communication will increase. However, field buses can often offer: better reliability, higher communication capacity, more communication channels etc.

The safety challenges of wireless communication can be tackled by using adequate protective measures. The reliability issues need to be adequate. This means that the bit error probability must not be too high. If the transmitters are moving or the environment is changing the connection can be lost. Therefore there need to be means to handle lost communication. 

For safety purposes it is important to be able to detect the correctness of the messages. If there is a defect, an error handling procedure must be executed. The properties that need to be controlled are:

 

  • message authenticity; originated from stated source
  • message integrity; complete and not altered
  • message timeliness; available at right time according to requirements
  • message sequence; correct sequence
It is possible to measure safety integrity and give worst case probability of undetected lost integrity. The value can be compared to the determined safety requirements. It is difficult to estimate probability of losing authenticity or timeliness. Therefore it is also difficult to assess the effectiveness of a specific protective measure. It is clear that there need to be protective measures against all relevant risks, but it is difficult to give probability values for each protective method. Here is this discussion in a nutshell: methods to protect integrity can usually be calculated and chosen according to determined requirements, methods to protect timeliness and correct sequence are usually adequate and methods to protect authenticity depend on the risks and determined requirements. When the limitations of wireless communication are kept in mind, wireless communication is a useful solution for safety-related applications, where wireless properties are needed.

Project duration: 01.01.2005 - 31.12.2006
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Project participants

  • Timo Malm

    VTT Technical Research Centre of Finland