IO-Link: Checking the ID avoids malfunction

IO-Link is a cost-effective and performance-optimised interface primarily used in automation to establish a connection between sensors and actuators at the field level. No direct links to complex fieldbuses are required, which means it can be integrated into all manner of systems worldwide. The reason why KELLER offers an IO-Link interface and has integrated this into our pressure transmitters is partly because of high demand on the market, and partly because we think that IO-Link has great potential and is set to become even more firmly established. 

Personally, I find the device ID verification function on IO-Link devices very useful. It means that the system only accepts IO-Link components which were taken into consideration when the system was developed. It’s not possible, for instance, to use a relative instead of an absolute pressure sensor or to use a pressure sensor with a different accuracy, pressure range or error band. It’s not ideal if a 4...20 mA temperature transmitter is connected instead of an analogue 4…20 mA pressure transmitter, for example. In that case the device would not be verified. Although the temperature transmitter does produce a plausible signal, it doesn’t have much to do with the intended physical measured value.

Thanks to the device ID verification, the system’s functionality is guaranteed even if the device is changed. Of course, this feature can also be built into CANopen, for example, but IO-Link comes with device ID verification as standard. 

IO-Link at KELLER

In order to implement this verification process across the board, we have decided to introduce a type code for device ID verification. So certain bits stand for
• pressure range
• type of pressure
• accuracy (as a total error band, of course – anything else is just superficial nonsense in my opinion)
• compensated temperature range

When it came to developing IO-Link products, we asked ourselves how we want to position ourselves on the market. We have, of course, retained key features such as the reliable and robust mechanical elements of our existing pressure transmitter. As someone with personal experience in control engineering, characteristics such as high bandwidth, short cycle times (no phase shifts) and low latency for the pressure switch output were very important to me. 

In terms of the accuracy of the pressure- and temperature-compensated pressure signal, we have used our 21Y and 23SY product series as a basis for the time being. This means we can produce the pressure transmitter in a cost-effective way. We understand that most systems in automation are not particularly demanding when it comes to accuracy. However, that would probably not be the case for a whole range of special and specific applications. 

We have developed a firmware platform consisting of individual modules, which can be configured according to the hardware used and the desired communication protocol. The modules can be inserted into the digital transmitters without much effort. It therefore doesn’t take much to integrate IO-Link into our high-end product lines (e.g. the X-Line).

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