News from Profibus / Profinet – Part 3 PROFIBUS — Device Management the Easy Way
Having more information about system assets is generally an advantage assuming that the information is accurate and consistent. To provide access to more information, a few things have to be put in place at the systems engineering level. However with Profibus, that is not a problem ...
Most of the former system operation, maintenance & service personnel had gathered in groups to reminisce about old times. Yes, a lot had changed on their production line. Opinions differed following the initial presentation by the young engineer. Some were happy that they had already retired. Others would have welcomed the opportunity to try out the new technology. The man with the beard sat alone at a table. He was not the type of person to show excessive warmth.
On the contrary, he always created the impression that he was grumpier and more unapproachable than he actually was. He has been involved in a lot of heated arguments in his day and had always probed the sore spots, but at times he could have been more pragmatic.
As a result, he did not rise as high in the organization as he otherwise might have done, but his expert opinion was always requested when technical decisions had to be made. The additional benefits offered by the fieldbus technology which the youngster had described were immediately clear to him. But did it not place major constraints on design and engineering flexibility and make spontaneous change virtually impossible?
Having more information about system assets is generally an advantage assuming that the information is accurate and consistent. To provide access to more information, a few things have to be put in place at the systems engineering level. However with Profibus, that is not a problem.
Profibus ensures maximum flexibility for the conceptual design, engineering and commissioning phases and guarantees uniform data structures across all devices.
Integration of field devices into the automation system is based on modeling of the device functionality in the control system. The GSD (General Station Description) provided by the device manufacturer acts as the electronic data sheet for the fieldbus device. It describes all of the functionality which the device supports. Users can then select which and how much process data will be transferred. Field devices detect this automatically, adapt accordingly and start communicating.
During the engineering phase, there is no need to know the details of the field devices that will be used later on. A neutral channel is used to define the channels. Hardware engineering is device neutral and is not reliant on the field device used. The devices actually used on the system do not have to be allocated until the commissioning phase. Segregation of communication and functionality simplifies the engineering work.
Defining Device Types
Since the basic tasks of the field devices are defined back in the engineering phase, it is a good idea to preselect one of six device types for the neutral channel. The list of choices includes:
- simple transmitters for one or two analogue process signals, e.g. temperature, pressure or fill level;
- multi-functional transmitters for up to ten analogue process signals, e.g. for flow metering;
- binary inputs and outputs;
- analogue positions for control valves and binary positions for valve boxes.
In general, measurement data is transmitted as scaled values, eliminating the need for scaling (data fitting) in the control system.
The old man cringed a bit when the man with the beard spoke up. Would the young engineer be upset by the man’s provocative manner? However he soon realized why the youngster had been chosen to give the presentation. Even now, he had no difficulty providing the answer and was not at all bothered by the bearded man’s grumpy disposition. However, the man was not about to let up yet ...
To be continued: Part 4
Further parts of our Profibus series:
Part 1: PROFIBUS – a Proven Technology
Part 11: PROFINET for Process Automation
Watch the video to find out more about the young engineer, the older man, the man with the beard and PROFIBUS PA.