There is still great potential for savings when wiring sensors and actuators. It is therefore only logical that IO-Link is now also opening up to the topic of wireless when it comes to field device wiring. The IO-Link community has been working on creating a specification for IO-Link wireless technology since 2016. The requirement profiles and use cases for this have been formulated and, based on this, the technical requirements have been defined and the specification document created in the corresponding technical working group.

The technical implementationThe technical implementation

The IO-Link Wireless working group has defined characteristics for the technology in order to be able to fulfill the defined requirements with IO-Link Wireless. One of the key specifications is that the application interface for cyclical data (process data) and acyclical data (on-request data) is compatible with the existing IO-Link description. This means that there is no difference for users whether wired IO-Link information or IO-Link wireless data is processed. In order to be able to handle the large number of devices, a master should be able to contain up to five transmission channels. Each of these supports a maximum of eight devices. This results in a total of 40 wireless devices per master. Three masters will be able to work in parallel in one cell. This results in a maximum number of 120 devices in one cell. A pairing service is implemented to assign the devices to the corresponding masters. A scan service enables 'unpaired' devices to be added to the system. For moving devices, there will be no limits on the speed at which they can move within a cell. A defined handover mechanism ensures the controlled roaming of devices between different masters.

IO-Link Wireless uses 2.4 GHz ISM band RF transceivers. The 2.4 GHz band is divided into 80 channels, each 1 MHz apart. General coexistence with other wireless systems is made possible by the so-called blacklisting mechanism - certain channels that are known to be used extensively by other systems are hidden from the outset. Within this fixed framework, 'frequency hopping' can be used. This allows a bit error probability of 10-9 to be achieved - similar to wired systems. In the future, it is planned that low-power devices will also be supported by the system. The cycle time is 5 ms. In order to comply with legal requirements, the transmission power is limited to ≤10 dBm (10 mW) EIRP. Nevertheless, an extension of 20 m is achieved within a master cell with one communication channel; with more than one communication channel, 10 m can still be achieved.

The specification is available

The specification for IO-Link Wireless has been available since Hannover Messe 2018. This is also where the technology was presented to the public for the first time in the form of a demonstrator at the PI joint stand.

Author:
Stephan Langer is Director Industry Portfolio Management Packaging, Food & Beverage at Balluff in Neuhausen auf den Fildern.