Fieldbus System Integrity and the Benefits of Modular Infrastructure

  • July 08, 2014
  • Phoenix Contact
  • Feature

By Jason Norris and Jason Nicholl, Phoenix Contact The worldwide adoption rate of Foundation fieldbus continues to increase every year. According to the Fieldbus Foundation, the market for fieldbus products exceeded $1 billion in 2012, and the installed base of Foundation fieldbus devices is already over $6 billion. Clearly, many users are already enjoying the benefits that fieldbus provides. When running industrial processes, maximizing system uptime is critical. As process automation becomes more advanced and devices more intelligent, monitoring the health of operations has now become an industry standard. With system diagnostics traditionally being rooted in the control cabinet and with typical fieldbus segment lengths reaching 1.9 km, one question stands out: Which would you trust more – the measurements from a multi-meter with test leads longer than 1 km or measurements taken in the field where the process is happening? This is the basis of the foundation for a “field diagnostics” approach, where the user can access diagnostics anywhere. A modular approach to Fieldbus can help achieve maximum availability and system integrity. Communication interruptions typically happen in the field, not necessarily in the control cabinet. Understanding this reality and combining it with modular field-based diagnostics can help achieve maximum availability and integrity of a fieldbus system. Managers and engineers are under extreme pressure to keep the plant processes online and maximize uptime where outages are simply intolerable. In Foundation fieldbus, noise is one of the biggest contributors for devices losing communication. Unfortunately, it is hard to diagnose exactly where the noise is originating, especially when making diagnostic measurements hundreds of meters away from the control cabinet.  

Figure 1: Dashboard overview of segment health

Every process engineer has a wish list that includes the highest uptime achievable, maximizing the most from the smallest electronics footprint and diagnostic information about the segment physical layer. Ideally, they want to:

  • Analyze the communication in precisely the environment that is affecting it the most
  • Take preventative action based on these measurements and keep the process from going down  
  • Do all of this from the control room in real time

Using the “diagnostics anywhere” approach, this can all be possible. Imagine being able to maximize real-time diagnostic accuracy without maintenance permits or process interruption. Similar to the popular handheld fieldbus devices, the new field-based diagnostics modules are designed to be placed directly into the field junction box, where they can record measurements without the assistance of maintenance personnel. This increases efficiency in maintenance costs. It also provides timely acquisition of real-time diagnostic data, which is critical to process integrity. The modularity concept coupled with field diagnostics is nicely complemented by the modular high-power trunk redundant Fieldbus conditioner. This employs both redundancy plus load sharing for maximum service life. These modular redundant FF power supplies mount on a DIN rail in the control cabinet, allowing for multiple bases to be stacked together for distributing bulk power to all modules. This flexibility allows the user to configure and control segment density within their control cabinets. A modular system allows the user to specify only what the system needs, which in turn yields the smallest footprint in the cabinet or field junction box.  

Figure 2: Detail of segment physical layer measurements

Second to that is a modular approach to device couplers. In many instances, there is a need to add an additional device to a live segment. When all the available spurs on a block-style device coupler are utilized, the user must add an additional block coupler to the junction box. The problem is that this can interrupt communication to devices in the field, while the new block is being wired in. With a modular approach, the user simply adds a new modular coupler to the existing junction box without interrupting communication, and the process remains online. Also, this gives the user the advantage of purchasing only what they need for the junction box while allowing them easy expansion if needed in the future. The modular “diagnostics anywhere” concept provides the foundation for maximized system integrity and availability in fieldbus control networks. When the user has complete control over where they measure the bus parameters, the real benefit of diagnostics is realized. With cable lengths exceeding 1 km, the information measured in the control cabinet is not always accurate due to cable losses. This can present a false sense of security, because noise levels and other critical physical layer parameters could actually be much higher in the field. Using field-based diagnostics, users can feel confident that they are reading real-time reliable system data, assuring them accurate assessment of their process integrity.

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