Revolutionizing Industrial Automation: The Impact of FDT and PI Technologies

May 22, 2024

Two different worlds

Rockwell Automation’s dominance in the North American automation market is reminiscent of Siemens’ parallel influence in Europe. Like Rockwell, Siemens boasts a comprehensive portfolio catering to factory and process automation applications. Additionally, Siemens has significantly shaped digital communications protocols, notably with its proprietary device description file format, PDM, based on the DDL standard.

Siemens gained a substantial edge over competitors with its fully integrated software solution, which streamlined hardware integration complexities across various versions of Profibus protocol variants.

However, as industry trends favored open standards, the need arose for a standardized management entity for Profibus and its derivatives. This led to the establishment of the Profibus & Profinet International (PI) organization, aiming to universalize Profibus across diverse applications through tailored profiles and adaptable technologies.

One such technology pivotal to PI’s mission is FDT/DTM, initiated by the ZVEI in 1998. This technology, finalized in 1999 and later overseen by PI, simplifies smart device commissioning through software drivers and standardized GUI, enhancing user experience and system integration for PLC suppliers.

The advent of FDT/DTM revolutionized the automation landscape, enabling PLC-based control systems to integrate diverse smart devices seamlessly, previously confined to proprietary protocols. This technology also served as a hardware abstraction layer, streamlining configuration tasks across multiple protocols and device vendors.

Moreover, FDT/DTM’s uniform interface mitigated the need for specialized training and troubleshooting, contrasting with the fragmented interfaces of EDDL, its text-based counterpart.

Profibus technology, with its DP and PA variants, initially offered significant advantages such as interoperability and cost-effective decentralized I/O systems. However, evolving industry demands, and the rise of Industrial Ethernet eventually eclipsed fieldbus solutions.

The emergence of Profinet by the early 2000s demonstrated flexibility and efficiency in factory automation, even though facing challenges in process automation integration initially. Yet, Profinet’s evolution, coupled with innovations like Ethernet-APL, promises seamless integration of smart field devices into industrial Ethernet networks, marking a significant stride towards Industry 4.0 and IIoT initiatives.

Profinet’s extensive suite of services facilitates diverse industrial automation applications, fostering transparent access across enterprise-level networks and enabling IT/OT integration on a broader scale.

The evolution of automation technologies driven by PI has unlocked a myriad of applications across industries, heralding a new era of interconnected and efficient industrial systems.

The Profibus communication model employs two distinct methods of data exchange to achieve the deterministic network behavior crucial for demanding applications.

Hiding Unnecessary Complexity Using Different Paths

In a Profibus network, a Class 1 Master sequentially polled all connected nodes, which responded with I/O data. This cyclic process occurred within defined time frames, allowing nodes to answer the master’s requests. Meanwhile, Class 2 Masters, utilizing periods of media downtime, could queue questions to connected devices.

Additionally, Profibus facilitated acyclic data exchange with connected nodes, allowing significant data collection and transmission. While this method lacked the determinism of Class 1 Masters, it enabled crucial exchanges like diagnostics, operation timings, and remote configuration, all without field intervention.

This prompted the birth of the FDT/DTM concept. Since Class 2 Masters, essentially Windows PCs, couldn’t use GSD files for acyclic communications, a device description coded as a small program, called DTM, worked with a framework application, FDT/Frame Application (Desktop Windows application). This concept, essentially the first Edge device, revolutionized integration.

At that time, discussions comparing FDT/DTM with EDDL, a text-based competitor, were ongoing. EDDL’s platform independence (e.g., from MS Windows) appealed to DCS suppliers accustomed to Unix systems.

Profibus featured two implementations: Profibus DP, an RS485-based serial fieldbus ideal for complex devices like RIO systems, and Profibus PA, leveraging the MBP protocol, offering power and communications to devices.

Profibus DP’s simplicity and interoperability with various RIO systems were advantages, but Profibus PA faced challenges over time. Despite its benefits, Foundation fieldbus was preferred by DCS suppliers due to its user layer’s compatibility with function block programming.

FDT/DTM’s constant user interface across different systems minimized training needs, garnering strong support from independent device suppliers and control systems.

As the industry shifted to Industrial Ethernet, Profibus faced challenges. However, Profinet, introduced by PI, gained traction for its flexibility, particularly in Factory Automation.

Profinet’s expansion into Process Automation faced obstacles due to integration challenges. Nonetheless, support for Ethernet-APL for this standard will enhance resilience and signifies ongoing evolution.

Ethernet-APL, a subset of SPE, promises a seamless transition from analog loops to digital networks, ensuring compatibility with existing protocols like Profinet.

Profinet’s comprehensive suite of services enables various industrial applications, promoting transparent access across enterprise networks and IT/OT integration.

Through PI technologies, a myriad of applications became feasible over the years, showcasing continuous innovation in industrial automation.

Profibus evolution through application examples

(with a little help from FDT/DTM)

Profibus DP-V1: Acyclic Data Exchange

The initial version of Profibus DP was dubbed V0, a name established for clarity following the introduction of V1. Profibus DP V0 exclusively facilitated cyclical data exchange. With the advent of Profibus DP V1, however, acyclic data exchange became feasible, ushering in the utilization of Class 2 masters. This advancement enabled remote configuration, parameterization, commissioning, and asset management practices through FDT technology.

The emergence of the first-generation FDT, tailored for RIO systems, capitalized on the modular device model embraced by PI. This development enabled remote detection of even minor faults, such as wire breakage or short circuits, on a per-channel basis.

Figure 1 – A Stahl IS+1 RIO system, with 7 standard multichannel I/O modules. This system supports 32 DI, 16 DO, 16 Ai and 8 AO signals. A Trebing +Himstead adaptor acts as the Class 2 master.

The introduction of support for acyclic data exchange enabled the transmission of HART data from the field devices to the Class 2 Master, marking another stride towards digitalization. Initially, this configuration utilized generic HART DTMs.

Figure 2 – A Stahl IS+1 RIO system, with 7 standard multichannel I/O modules. This system supports 32 DI, 16 DO, 16 Ai +HART and 8 AO + HART signals. Generic DTMs were used initially, since full support from the industry was not yet available.


FDT technology found itself in competition with another standard for device description, namely the EDDL standard, which represented an advancement over the original DD files used for HART devices. EDDL technology formed the backbone of Siemens’ PDM asset management solution and Emerson’s FHX descriptors included in the AMS device installation kits.

The widespread industry support for the FDT concept fostered a market for third-party DTMs, aimed at integrating field devices from manufacturers that did not offer FDT support. For instance, Siemens’ ET200 series of RIO systems lacked FDT support, prompting independent companies like Softing AG and others to develop DTMs facilitating the integration of these devices into non-Siemens environments.

Figure 3 – An ET-200M Siemens RIO system connected to a Softing adaptor working as the Class 2 master. The ET200 DTM works like a Gateway DTM for the connected HART devices corresponding DTMs.

Profibus DP V1 introduced the concept of nested networks, facilitating the integration of HART AI and AO I/O modules. These modules could now transfer data from connected field devices using acyclic communication methods, effectively transforming any HART I/O module into a HART gateway.

This innovative solution simplified the utilization of HART devices compared to traditional methods reliant on serial multiplexers, known for being slow, costly to install, and challenging to maintain. Profibus DP V1 thus provided a practical means to leverage HART technology.

Intrinsically safe Profibus remote I/O systems

However, the initial generation of Profibus RIO systems lacked support for hazardous area applications, a common requirement in the Process Industry. To address this need, three alternative approaches emerged:

1. RIO systems equipped with a power supply capable of delivering intrinsically safe power levels to the I/O modules via IS power channels. When a channel reaches its limits, the remaining modules switch to the second IS power channel until all modules are powered or the power supply reaches its maximum output. Notably, this method obviates the need for a certified cabinet to be installed in a hazardous area, even in Zone 1 applications.

Figure 4 – Stahl IS1 RIO system equipped with 5 galvanically isolated, IS I/O modules. The system has one 16 ch NAMUR DI module, one 6 ch DO module for IS solenoid valves, one 8 ch AI module and one 8 ch AO module with built in HART modems.

Stahl was the first to introduce such a solution, followed closely by Siemens, which notably did not support the FDT concept. Consequently, third-party suppliers stepped in to develop DTMs for the IS RIO solution.

Figure 5 – A Siemens ET 200ISP using a Softing DTM for integration into a Prosoft Class 1-2 master. The RIO system is intrinsically safe and works as a HART modem for connected field devices.

2. RIO systems utilizing backplanes equipped with Ex e protection. These systems necessitate the use of certified Ex eb increased safety cabinets for field mounting in Zone 1, which, while pricier than simpler non-certified counterparts, offer streamlined installations and performance. Their power supply typically comes at a lower cost compared to a multichannel IS one.

Moreover, these systems allow for mixing Ex and non-Ex modules within the same cabinet, reducing the total number of required housings and yielding significant savings.

3. RIO systems with Zone 2 approval. This is the most frequently used solution. It offers slightly lower savings in cabling but deliver similar functionality to the previous options with much lower costs per I/O point. These systems require the use of Ex ec certified housings.

Rebranded RIO systems and Universal I/O modules

To minimize development costs, some DCS suppliers opted to offer rebranded versions of existing RIO systems or collaborate with experienced third-party suppliers to either design new RIO systems or adapt existing ones to their requirements.

For example, Turck’s ExCom RIO system, originally developed by Turck, was also marketed as the S-900 RIO system featuring ABB colors and logos. Similarly, Rockwell’s Flex IO Ex system was designed by P+F, which also sold it as the IS-RPI system.

These systems push FDT technology to its limits: each module is equipped with a DTM. Consequently, with an 8-channel DI module, users can configure each channel according to the application’s requirements. Moreover, the built-in diagnostics enable the detection of wire breakages, identifying the malfunctioning module and channel with precision.

Figure 6 – Turck´s Excom RIO system with these modules: 2×8 ch IS DI NAMUR, one 8 ch IS DO, one 4 ch IS AI HART, one 8 ch IS AO HART, a 4 ch temperature input and a frequency monitor- The HART data from the field devices is sent to an asset management workstation.

Another significant advancement in RIO systems was the introduction of universal I/O modules. Originating from the Smart I/O systems developed by major DCS suppliers, this innovation aimed to streamline I/O module variety by employing a single module configurable to connect DI, DO, AI, or AO signals via software. Each module encompasses the necessary electronics to accommodate any of these four primary types of I/O signals.

This approach offers several benefits, including a reduction in the variety of commonly used modules from four to one, resulting in fewer and more standardized spares and simplifying the marshaling stage. This concept seamlessly aligns with both FDT and Profibus DP technologies, owing to the modular nature of the device information model implemented in these standards.

While initially promising, the added electronics required to support the four different I/O signals increase the module’s cost. Additionally, given the prevalent usage of DI signals in typical process automation applications, allocating one of the configurable module’s channels for the most frequently used signal could render the overall installation expensive. Consequently, universal modules may prove more practical for AI/AO signals exclusively.

Figure 7 – P+F´s LB RIO system equipped with Di, DO, AI, AO, frequency monitoring and universal IO modules, both in IS and non-IS versions.

Profibus PA and third-party solutions

PI’s implementation of the IEC 61158-2 standard is known as Profibus PA fieldbus. This serial protocol utilizes the MBP (Manchester Bus Powered) encoding method to provide both power and communication to intelligent Profibus PA field devices. Due to differences in physical layers between Profibus PA and DP, a linking device is necessary to connect them. Initially, two alternatives emerged, evolving differently as Profibus DP increased in speed.

The available options were Siemens’ DP/PA Link and P+F’s SK2/3 segment couplers. Siemens’ approach functioned as a RIO system for Profibus PA, while P+F’s solution operated as a proxy server. Notably, Siemens did not provide FDT support, whereas P+F’s approach did not require a driver or device description.

Third-party DTMs soon emerged to facilitate configuration of Siemens DP/PA links, while P+F’s SK3 segment coupler offered an FDT/DTM-based fieldbus diagnostic module. Once again, the flexibility and adaptability of FDT technology positioned it as the optimal solution to meet industry demands.

Figure 8 – Siemens DP/PA links integrated in a FDT framework using third party DTMs supplied by IBHsoftec and Softing

Advanced fieldbus physical layer diagnostics

The option of running complex applications in the FDT framework using DTMs enabled several suppliers of PROFIBUS diagnostic tools to develop sophisticated diagnostic solutions. From handheld physical layer diagnostic tools to advanced applications that made diagnostic information available across Ethernet networks, to comprehensive commissioning tools that could be integrated with most major DCS suppliers, the FDT concept emerged as the premier method for implementing state-of-the-art PROFIBUS DP and PA installations.

Figure 9 – P+F´s Fieldbus Advanced Diagnostics system solution, based on FDT technology, shown in stand alone and Profibus integrated setup options

The third generation of P+F’s SK transparent DP/PA segment couplers included a modular fieldbus diagnostics solution, which is among the most ambitious FDT/DTM applications ever designed. P+F’s diagnostics module can be utilized in various ways: integrated into the PROFIBUS network, as a standalone handheld device, or as a plant-wide, Ethernet-connected, FDT-based diagnostics network that can even interface with OPC.

By 2010, after several years of limited options, many solutions were available for connecting PROFIBUS PA networks not only to PROFIBUS DP but also to other protocols. The slower-than-expected adoption of FOUNDATION Fieldbus left process automation users who were interested in fully digital communication protocols with PROFIBUS PA as their primary choice.

Figure 10 – Diverse Profibus PA from Siemens, P+F an E+H field devices connected to a Class2 Master equipped with a Procentec/Phoenix Contact DP/PA coupler.

Procentec’s CommBricks DP/PA coupler with integrated fieldbus diagnostics uses a DTM file for configuration. This device resolved a decade-long debate between advocates of P+F’s transparent, proxy-like couplers and proponents of Siemens DP/PA PROFIBUS PA RIO-like systems. Procentec’s innovative solution allows users to select the desired behavior via an option in the device’s configuration.

The PROFIBUS standard, in conjunction with FDT technology, enabled the integration of both DP and PA network segments into other networks. Rockwell’s Hiprom series of PA linking devices allowed the integration of PROFIBUS PA field devices into EtherNet/IP networks, gaining some acceptance in the mining industry before being discontinued, potentially leaving numerous plants without options.

Options for brownfield applications

The flexibility and widespread market adoption of FDT technology have created an interesting market for third-party suppliers of both PI-compatible hardware and software. This is particularly beneficial for brownfield plants that need to extend the lifecycle of their control system installations.

Aparian Inc. addressed the discontinuation of Rockwell’s Hiprom-branded linking devices by developing a PROFIBUS PA to EtherNet/IP proxy, providing end users with an upgrade path.

Figure 11 – Profibus PA field devices connect to a Rockwell PLC using the FactoryTalk Linx Comm DTM

Aparian also offers a FOUNDATION Fieldbus to EtherNet/IP interface, further expanding the integration options for industrial automation systems.

Figure 12 – Schneider´s PRM (Profibus Remote Master) working as a Class1/2 Master connected to a Stahl RIO system, which offers HART Gateway compatibility. Additionally, Profibus PA support is offered by P+F´S SK3 DP/PA Segment Coupler which also includes an Advanced Diagnostic Module for the PA network.

Profinet for PA

In the past decade, PROFIBUS DP has gradually been replaced by PROFINET-based networks. PROFINET offers superior integration with other networks thanks to its detailed proxy-based interface gateway description, which standardizes all connection requirements with other industrial networks. By using a PROFIBUS PA to PROFINET proxy, PROFIBUS DP networks can be seamlessly migrated to PROFINET, ensuring that PROFIBUS PA-based process networks are not left behind.

Ethernet APL and the future

The latest innovation in Process Automation communications is Ethernet-APL (Advanced Physical Layer).

Figure 14 – Ethernet-APL Field switches scan work as Profibus PA proxies for backward compatibility purposes

This technology, a subset of the SPE (Single Pair Ethernet) standard, enables Ethernet to reach the field device level using standard IEC 61158 cabling, which delivers both power and communications. It supports intrinsic safety through Ethernet-APL field switches that include physical layer diagnostics. Utilizing FDT/DTM technology, these field switches can also function as PROFINET PA proxies, allowing end users to perform a phased migration to the new technology.

From its inception, the FDT/DTM concept has continuously demonstrated adaptability, enabling innovations such as advanced diagnostics, nested networks, and fieldbus physical layer diagnostics. It has extended the life of HART technology by allowing RIO systems to function as HART gateways and has provided PROFIBUS connectivity to platforms not originally designed for it.

The FDT Group, now working in cooperation with FieldComm Group, embarks on a new era of developing innovative solutions to enhance field device integration into next-generation control systems.

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