Device Integration
Easy field device integration on PROFIBUS
On fieldbus systems, the functionality of field devices must be integrated on the control system to enable it to access the field device functions during operation. Manufacturers describe device functionality in a textual (GSD, EDD) or software (DTM) file which the user integrates on the control system using a software tool.
Device integration is not needed with 4-20 mA communication, because there is only one type of data – the measured value – to be exchanged with the control system. However, users will inevitably compare fieldbus device integration with the “simplicity” of traditional 4-20 mA technology whereat “simplicity” is more or less a synonym for long time experience and user friendly procedures which do not require any special knowledge.
In fieldbus technology, however, for many users experience does not yet exists. All the more, to compete with 4-20 mA in simplicity, the procedure of fieldbus device integration has to be user friendly and must not require any prior knowledge of digital communications technology. This is precisely what the PA Profile 3.02 achieves.
Mistake-free device integration
Field devices and their description files are compatible if they share a common set of functionalities. Mandatory compatibility rules for both description files and field devices are the key to simple and confusion-free device integration as realized in PA profile 3.02.
- The rules stipulate standardized parametes to be stored in the device and the respective device description. This enables integration tools to automatically assign devices and description files which means considerable simplification during the initial installation or device replacement. Figure 1 shows a conceptual view of a description file – device compatibility verification.
- Further rules are defined for device software upgrades and the effect upgrades have on the compatibility and identification of the device version and device description.
- Readily understandable identification marking is also placed on the outside of the device, so that the device can be associated with a description file even when the device is not switched on.
Interruption-free replacement
Using proprietary device descriptions, the user was often forced to install an identical device during device replacement instead of utilizing the advantages of further developed (alternate) devices. The PA Profile 3.02 eliminates this shortcoming by the capability of devices to automatically assume different roles.
The GSD file of a device is definitely associated with the device by the Ident number. During the process of “Automatic Ident Number Adaption” of the alternate device, the control system automatically informs this device about the role and tasks of the former device, defined by the Ident Number. The alternate device then will automatically switch to the internally stored functionality of the former device without interrupting the process. Thus, replacement of a Profibus PA device becomes similar to replacement of a 4-20 mA device.
Fig. 2 shows a conceptual view of thes procedure.
The same applies to EDD or DTM files when a device is replaced. The identification rules for the EDD/DTM and the device make it possible to uniquely determine compatibility with different versions.
Fig. 1: Confusion-free device integration
Fig. 2: Interruption-free device replacement