In order to achieve the system performance of hard-wired sensor-actuator systems with wireless technology, it is important to realize different requirements.
Dec, 2018 – The cabling of sensors and actuators still offers great savings potential. It is only logical that in terms of field device wiring now IO-Link opens the subject of wireless. As early as 2016, the IO-Link community is working on the creation of a specification for the IO-Link wireless technology. The requirement profiles and use cases for this purpose were formulated and the technical requirements were defined and the specification document created in the corresponding technical working group based on this.
In order to achieve the system performance of hard-wired sensor-actuator systems with wireless technology, it is important to realize different requirements. For example, a cycle time shorter than 10 ms for updating the I / O data is required. The demands on the reliability are at least as high as with the wired systems. More than 30 devices should be able to communicate with a master via a radio channel. As a frequency band, the 2.4 GHz band will serve – the coexistence with other systems on this frequency band is a prerequisite. In addition, within a high-frequency range, up to three masters can communicate with a total of up to 120 devices.
Previous wireless technologies do not fully meet these requirements. WiFi, for example, fails in the requirement for reliability and determinism through the used Listen before Talk mechanism. With Bluetooth, neither the required number of subscribers nor the real-time requirements or problem-free coexistence with other technologies can be realized. Zigbee also can not guarantee the target update rates, as the data rate of 250 kbps is too low for 16 frequency channels used and 5 MHz bandwidth. Wireless Hart, on the other hand, does not achieve the speed required in factory automation with a cycle time of a few 100 ms.
