Fieldbuses for machines
Original article date: September 1999
Devicenet is becoming more popular and is being used on smaller plant and machines, as our man John McGreal finds out
It is hard to believe that Devicenet was only launched in 1995. Since then, this open fieldbus system has matured, largely as a result of the wide range of products that are now available for connecting to it. Indeed, the second generation of Devicenet components is proving to be physically smaller and priced lower – now comparable with conventional devices – which counteracts two of the traditional arguments against device-level fieldbuses. But one of the trends to have emerged more recently is that more users are turning to Devicenet for smaller assembly cells and individual machines. So why is this?
Looking more closely, it is apparent that many users are finding Devicenet is particularly useful for using inside control cabinets – and this tends to lead to it being used beyond the control cabinet as well. But inside a control cabinet, Devicenet saves space, makes the connection of components such as drives and soft starters far quicker and, perhaps more importantly, gives access to data that simply was not tapped into previously. This issue is usually of more importance to the end user than to the panel builder or machine designer, because access to data means that diagnostics are easier and maintenance can be carried out more efficiently.
Another reason why Devicenet is increasingly being used at a machine-level is that production lines are often assembled from several machines, some of which might come from specialist suppliers. If a fieldbus is used, it is simpler to build and test the individual machines, as well as to assemble and test the complete production line.
A new Devicenet development announced by Rockwell Automation is the Armorblock Maxum connection block. This builds on the success of the Kwiklink (which allows rapid connection to a profiled four-wire connector) by adding smart I/O diagnostics. Rockwell says: “Armorblock Maxum makes full use of Devicenet’s advanced communications capabilities such as short-circuit, open-wire and no-load detection, auto-baud selection, selectable I/P filter times and self-configuring PNP/NPN inputs. Armorblock Maxum opens up a whole new world of I/O diagnostics.”
Any other questions?
Covering a broader range of topics than just Devicenet, there is a seriously useful booklet available from Rockwell Automation entitled Industrial Communications Networks. This is written in a reader-friendly question-and-answer format and should help you to decide whether a fieldbus (of any variety) is right for your needs and, if so, what types you should be considering. It’s the sort of guide that your colleagues will want to borrow!
- Rockwell Automation
September 1999