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IO Link: open interface standard for fieldbus-neutral sensor/actuator communication
Waldkirch, April 2006 – First the WT18-3 photoelectric proximity switch was presented as the first standard sensor with a fieldbus connection at the HMI 2005. Then the first machine (from Meurer Verpackungssysteme) with the new sensor generation appeared at Interpack 2005. Since then the concept of the IO Link sensor communication interface, initiated by SICK, has become established as a technological trend. The open IO Link standard is now supported by numerous sensor producers and has been accepted by the German Electrotechnical Commission (GEC) as a standardisation proposal for the International Electrotechnical Commission (IEC).

The most important advantages offered by IO Link are increased plant availability, comprehensive remote diagnosis capability, automatic plant documentation, and – of importance for the chemical and pharmaceutical industries – the possibility of validating entire machines. Which is why, in the relevant segments, fieldbus-enabled sensors like the WT4-3, WT18-3 and WT27-3 photoelectric proximity switches have very quickly received the attention that experts had predicted.

Basis: the special sensor concept

The technological background for a reasonably priced upgrading of the switching output of a sensor to a communication interface is a new ASIC-based concept for photoelectric switches and, in particular, proximity switches. In addition to the electronic setting of scanning distance and background suppression, it permits the detection of numerous other states in the vicinity and the sensors themselves. At the same time, IO Link allows the controller to communicate with the sensor, to parameterise it, or even to download entire parameter sets, e.g. when there is a batch change.

IO Link is not a classical bus system, but a fieldbus-neutral point-to-point connection for dialogue between sensor and controller. The physical coupling of one or more sensors to a fieldbus takes place with the help of an IO Link connection module.

Sensors perceive more than just objects

The new concept, however, not only permits the transfer of considerably more information than just digital switching states and digitalised analogue values. The substantial supplementary information that can also be transmitted includes, among other things, pre-contamination warnings, the presence of sources of interference in the sensor surroundings, the quality of the switching signal, the current scanning distance, or the sensor’s serial number. Dialogue between the sensor and the automation system also opens up completely new perspectives during the design, construction, installation, operation and maintenance of machines. These potential advantages have also been recognised by other sensor producers, automation suppliers and machine manufacturers. Which is why they support the standardisation proposal for IO Link at the IEC (via the GEC).

Open, easily implemented and a safe investment for the future

Machine constructors, as well as their users, can easily and rapidly profit from the advantages offered by IO Link. In addition to the use of communication-enabled photoelectric proximity switches, e.g. the WT4-3, WT18-3, and WT27-3 from SICK (or corresponding sensors/actuators from other producers), only an IO Link connection module is required for a fieldbus connection. This now permits connection of up to four sensors via unscreened, three-pin standard cables. The concept is thus compatible with the switching and connection technology common up to now. It is also possible to connect sensors that are not communication-enabled, though these cannot exploit the advantages offered by IO Link.

Speed is unimpaired

The numerous advantages offered by IO Link are not achieved at the cost of process speed. The rapidity of the communication is sufficient to exchange process data within two milliseconds. The concept can be expanded with a real-time output for very rapid switching processes.

Standardisation almost achieved, users in the starting blocks

Standardisation of IO Link, initiated by SICK and supported by other companies, will shortly be completed. Most of the specification has already been defined and agreed. Correspondingly, numerous users and machine producers are merely waiting for the products to become available. Three sectors will be the first out of the starting blocks.

In the pharmaceutical industry IO Link supports, among other things, rapid changes in ingredients and the validation of entire machines and plants, right down to sensors/actuators.

The packaging industry profits through the automation of format changing processes, as well as the adjustability of critical applications in which high accuracy and reliable reproducibility are vital.

In handling and warehousing systems, IO Link makes it possible to see with the “eyes” of the sensor from distant locations. If faults occur, rapid identification of the cause is possible.

Summary: IO Link will have positive effects on the design and control technology of machines and plants in future. Largely passive function elements will become active participants in dialogue with the control level and, in addition to switching signals, will autonomously report errors and supply state information. IO Link is thus the sensor communication of the future. In the simplest of ways, it also integrates the technologies that have hitherto been common, and is thus an investment with a very safe future.