Automation Technology and the keywireless Profibus
Automation technology is a term that cannot be grasped completely, but still has an important position in the industry, as the application created by it makes it possible to automate internal system processes and the secure processes. This technology creates a secure data transfer between the participants of a network, so that they can communicate with each other and can initialize work steps. The aspect of safety is served by periodic independent and mutual diagnosis and determination of current state values.
In automation technology, transfer takes place via fieldbuses that may operate wirelessly and transfer the data packets to the respective receiver via digital or radio-controlled interfaces. The Wireless Profibus is a special fieldbus serving the wireless transfer via a wireless interface.
The Operation of the Wireless Profibus
Although this type of data transfer does not use a classical cable interface, the wireless link appears like a cable from the technological point of view. The employed system is a master-slave connection where one of three components is designedfor cyclic data transfer from the master to the connected slave:
- Programmable logic controller (SPS)
- Programming device
- Operator panel
However, there is also a challenge with wireless transfer when the data needsto be transferred from the Wireless Profibus to the cable interface in orderthat the data liesin the range of 9.6 kbps tomax. 12 Mbps. Realizing this requires strict observance of the timings. Only in this way is it possible to guarantee the interference-free operation that is key to this process.
Approaches to the technological challenge with the Wireless Profibus
Keeping the timings is not always possible with a conventional transfer via wireless links, so that the principle of keying must be used, where a light beam device takes the position of the medium to be transferred. To enable wireless transfer with the Wireless Profibus nevertheless, three different approaches are available.
- Wireless modem as gateway – with this realization option, the telegrams are not set by radio. Here however, a slave function is found in the wireless set. Amongst other things, the data framework is defined by integration of a master by means of a GSD file, a file containing the device master data. Then, the radio channel isonly used for exchange of the net data with the gateway approach. However, this option has the disadvantage that the many mechanisms for monitoring, which are integrated in the Wireless Profibus, cannot be used. However, the advantage is that the uncoupling of the timing from the respective wireless link simplifies the technical realization.
- Transparent wireless transfer with change of the timing – this is the second solution option for the problem of the technical challenge. With this approach, the cyclic data transfer of the Wireless Profibus is slowed down so far that a considerably longer answer time is available. This is done by insertion of long pauses between the individual telegram transmissions. This slowdown makes it possible to operate the bus within the span from 9.6 kbps to at least 93.75 kbps. In doingthis, the TSLOT time has an increased maximum value of 16000 bit times. However, there are also two essential disadvantages here for the Wireless Profibus, namely loss of the ability to connect fixed wire participants to the same master and triggering of faults at the master by interruptions of just 100 ms. However, the reduced costs through the use of simple and cheap radio modules is an advantage.
- Transparent wireless transfer without change of the timing – this last solution approach is based on exclusive wireless transfer of changes. With this, the data is initially received at the cable interface of the radio module, with the precondition that an extremely high data rate exists. Afterwards, the cyclic redundant data isremoved. By using this procedure, the Wireless Profibus can be used so that the wireless link, from the technical point of view, behaves like a cable. By doing this, all diagnosis functions of the technology can continue to be made available, and any masters and slaves can be hooked up. A further advantage is the time monitoring function that is triggered in the wireless system only when a freely parameterized time has elapsed, after which the interruption is executed
The Profibus Technology
PROFIBUS, which in addition to a universal fieldbus is also the basis for the Wireless Profibus, was developed by the Siemens AG and the corresponding user organization of Profibus. The main areasof application arethe automation manufacturing operations, processes, and in building technology. In this way, this standard specified in the international standard series IEEC 61158 specifies the technical characteristics of serial fieldbus systems, by which various devices can be networked from the field level to the cell level, so that automation becomes possible. Wireless Profibusis thus based on a recognized standard where the protocol architecture is basedon the OSI reference model, so that a multi-master system is created, which enables joint operation of automation systems.