What follows is an excerpt from the recently released White Paper entitled 6 Reasons to Give PROFIBUS PA Another Look.
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 system’s 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. A neutral channel is used to define all of 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. Among others, the list of choices includes:
- Simple transmitters for one or two analog process signals, e.g. temperature, pressure or fill level
- Multi-functional transmitters for up to ten analog process signals, e.g. for flow metering
- Binary inputs and outputs
- Analog 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.