Opening up the field

The degree of automation in the process industries is growing enormously. Manufacturers of all kinds of devices are implementing more and increasingly complex functions in their products.

As a result, the demands on operators are rising, while at the same time workflows need to be streamlined. In particular, the configuration, parameterisation and diagnosis of field devices is taking on increasing importance.

In addition, the wide range of components available means that field devices can be selected to best suit the individual applications. The consequence, however, is the use of real multi-vendor installations. But access to all the different parameters and functions is traditionally only possible using vendor-specific tools.

A first approach to allowing standardised access to devices was made with DDL (Device Description Language). This solved the problem of the vast variety of manufacturers and devices by providing a text-based language that describes the features of the devices that are used. DDL serves to develop a device description, which indicates the parameters for field devices and supplies digital information. This information may include, for example, the device status, process data and information about the current configuration.

The trend, however, is moving towards increasingly complex applications in field devices. The graphical representation of device information, the performance of algorithms on parameters and the display of real-time trends are all requirements that can no longer be met using DDLs.

Moreover, Hart DDL, Profibus EDDL and Foundation Fieldbus DDL can only be used within their communication or fieldbus boundaries, even though they may well co-exist in multi-vendor installations.

This is where the basic idea of FDT - Field Device Tool - technology starts. Its architecture allows all parameters to be merged independently of the fieldbus, manufacturer and device.

Access to the field device is precisely defined in the specification. The first advantage is that it ensures easy and uniform parameterisation. At the same time, it offers sufficient freedom to represent even complex field device functions in a simple user interface.

These benefits apply to both the manufacturer of automation products and the user. As a result, FDT technology is currently enjoying an increasing rise in acceptance. Well-known suppliers of devices and systems for the process industries, such as ABB, Metso, Invensys and Endress+Hauser, have already committed themselves to FDT. Interestingly, more and more manufacturers from the factory automation arena are joining them, companies such as Moeller and Siemens.

Originally developed for Profibus PA, FDT technology is now also available for Hart. An international group of vendors is also currently working at getting the specification for Foundation Fieldbus ready for release. Demo applications have already been presented at several trade fairs in Europe and the US, and commercial applications can be expected soon.

But how does FDT actually function? The central component of the FDT concept is the Device Type Manager (DTM), the device driver which the manufacturer supplies together with the device. The DTM knows all the rules of the device, contains all user dialogues, carries out the device configuration and diagnosis, and generates the device-specific documentation. Engineering tools - so-called FDT frame applications - load the DTMs of all the devices of an installation as 'containers'. Over the standardised FDT interfaces, the engineering tool utilises the information and functionality provided by the DTMs.

To make this technology even more attractive for operating companies, a migration path is available for all types of existing device descriptions. Hart DDs, Profibus EDDs and Foundation Fieldbus DDs can be migrated to DTMs via converters, seamlessly integrating into FDT.

The only thing that is missing now is a standardised way of addressing the field device independently of the fieldbus. This is accomplished through communication DTMs (Comm DTMs). A Comm DTM is the configuration and management tool of a communication module. A simple example of such a communication module would be a fieldbus PC card. Far more interesting is the use of gateways, which extend the full range of FDT advantages by the possibility of remote access.

Such Comm DTMs provide any DTMs with a communication channel for data exchange with the devices. The specific properties of a fieldbus or of the communication module are encapsulated by the FDT interface of the Comm DTM.

Examples of a complete Comm DTM architecture can be found in products from Softing, a company well versed in the technologies involved in the FDT concept. Based on tried-and-tested hardware and software components, access to Profibus and Foundation Fieldbus devices is offered via Comm DTMs. For Profibus, for example, a complete range of interfaces (ISA, PCI, PC/104 and PCcard) are available, as well as the Profibus Ethernet gateways FG-100 and FG-300 Profibus. The PROFIdtm Comm DTM can be used with any of these platforms.

By actively scanning the entire Profibus address space, PROFIdtm finds all the devices that are connected in a plant. The found devices are added to a 'live list' and displayed in the engineering tool together with their names, addresses and Profibus identification numbers. The DTMs that match the Profibus IDs can be automatically loaded into the engineering tool. Parameterisation and diagnosis of devices can thus be performed immediately, practically without manual operation.

A further simplification offered by PROFIdtm is the possibility to set the device address from the engineering tool. This is particularly useful for devices supplied with a default address that is incompatible with the project. The tiresome need to go over all the devices in the plant in order to change the device address on site with a handheld terminal is therefore eliminated.

To sum up, FDT allows the simple and uniform parameterisation and diagnosis of devices from different manufacturers. The more intelligent the devices and the more parameters needing to be set to use them, the more the benefits of FDT take effect.PE

Armin Tesch is Softing's international sales manager for industrial automation.