Major Difference between Foundation Fieldbus and HART Protocols - Emerson Automation Experts

Major Difference between Foundation Fieldbus and HART Protocols

Over in the peer-to-peer Emerson Exchange 365 community, a question was asked in the Valve Controllers & Positioners track:

Major difference between FOUNDATION Fieldbus and HART Protocol

I would like to know the major pros and cons of Fieldbus over HART. I was only aware of the fact that HART is analog communication and Fieldbus is digital communication. Is there any other major difference among the 2 protocol?

Emerson’s Jonas Berge responded [hyperlinks added]:

Emerson's Jonas BergeBoth HART and FOUNDATION fieldbus (FF) are good. You can’t really compare pros and cons of FF versus HART. HART is good for configuration, calibration, diagnostics, and viewing internal variables – what is usually referred to as intelligent device management (IDM). However, FF is used for both IDM and also for real-time closed loop control which HART does not do. This is THE major difference between these two protocols – which you already pointed out. If your field instruments use HART, then your control system must use 4-20 mA for closed loop real-time control since HART does not do that. Since FF provides both the IDM and real-time control functions digitally, you cannot really compare it to HART which only does IDM. I guess for a full picture you would need to compare FF to on/off and 4-20 mA with HART. The reason being that many of the differences between a FF system and a system using 4-20 mA/HART is not in FF vs. HART but in FF vs. 4-20 mA and on/off.

Since FF is digital, it has several benefits over loops using hardwired 4-20 mA and on/off signals. For a full explanation of FF benefits refer to the brochure found here:

I personally think the highlights include:

  • Real-time closed loop control completely digital end-to-end, from sensor to actuator
  • More current for more powerful two-wire loop powered devices like radar level transmitters, multi-channel temperature transmitters, and more diagnostics etc.
  • Balanced (non-grounded) signal with high amplitude for noise immunity
  • Intelligent discrete devices like two-wire on/off valves
  • Multiple devices on the same pair of wires reducing cable, tray, junction boxes and associated labor
  • Multiple signals (per device) on the same pair of wires dramatically reducing cable, tray, junction boxes and associated labor
  • Dramatic reduction of I/O cards reducing system footprint and weight
  • Elimination of I/O card selection simplifying engineering
  • Elimination of safety barrier selection simplifying engineering
  • Elimination of signal marshalling simplifying engineering
  • Easy addition of devices
  • Easy addition of signals in devices
  • Easy to change design to other device type: e.g. on/off valve to control valve or MOV
  • Time synchronized control
  • Fast control response period
  • No 4-20 mA range mismatch
  • No 4-20 mA current calibration skew
  • Signal distortion detected
  • Measurement over full sensor limit (no 4-20 mA range)
  • No 4-20 mA five point loop test
  • Real-time PV validity indication
  • Position feedback on every valve
  • Multi-channel temperature transmitters
  • Advanced device diagnostics
  • Centralized firmware upgrade

As you can tell, most of these points are really FF advantages over 4-20 mA and on/off signals and have nothing to do with HART.

Having said that, 4-20 mA and on/off signals will continue for years to come. We still have a lot of 3-15 psi pneumatics. Some plants feel their personnel are not ready for digital devices, computers, and Internet downloads – although that is changing rapidly thanks to the proliferation of smart phones. And for sure, a plant using 4-20 mA with HART is FAR better than a plant using only 4-20 mA or proprietary smart protocols. In far too many plants the control system either does not support HART pass-through, or the HART pass-through has been disabled due to installation issues causing communication errors. In my personal opinion, if the system doesn’t support HART pass-through, it should either be upgraded or the instruments should be fitted with WirelessHART adapters. Installation issues causing communication errors should be fixed such that HART pass-through can be enabled for every device. IDM software should be installed, implemented, and incorporated in daily maintenance and turnaround planning. This way the plant can fully enjoy its 4-20 mA/HART devices.

Also, until recently FF was not as easy to use as it should have been – particularly in ‘other’ control systems (pardon the shameless plug for easy DeltaV). Some aspects were complex or were MADE more complex than it would have to be. Over the past 15 years the FF technology has improved dramatically, as has the implementation of the FF technology in devices and systems – much thanks to increasingly demanding testing of devices and systems. Some of these improvements, like EDDL, have also made 4-20 mA/HART devices easier to use. Another example is the award winning DeltaV fieldbus card with integrated power:…/emerson-wins-asia-manufacturing-awards.html

Make sure to use an FF system which is registered to profile 61 compliance level ‘b’ of the Host Profile Registration (HPR) process:

If you have an old control system using FF, make sure to upgrade to a version which is 61b registered to enjoy the capabilities that it entails.

You can learn more about intelligent device management (IDM) here:

As we get closer to the Emerson Exchange conference in the Dallas/Fort Worth, Texas USA area, make sure to follow the action in the Emerson Exchange 365 community. We’re planning to have a live page with video, news, blog posts, tweets, and all the action we can possibly share with you.


  1. kalpesh patel says:

    nice system…………….

    • Dan Daugherty says:

      I kind of see it as something similar to the transition between using a typewriter v using a computer and printer in terms of adoption attitudes. I remember a lot of people had typewriters and the idea of having to set up and learn a computer with its ever changing software revisions seemed unnecessarily onerous. But a new generation came along knowing nothing of typewriters and is completely at home and at ease using a computer to do what was once done with a typewriter… and more.
      Techs and engineers who come out of technical schools these days are not afraid of FF. It has only gotten better, and it will only get better. The dinosaurs will retire and all of this will just be a story someday.
      I cannot add to Jonas’ post. I would however offer my own pareto ordering of values over 4-20ma with HART:
      — at the DCS, a set of redundant communications cards offers extremely high reliability, saves space in cabinet by connecting to double or more of the number of I/O points as regular point-to-point I/O, can get all elements of a loop on one communication channel to increase the reliability, and provide superior control loop performance with low latency while off loading clock cycles from the main controller CPU.
      — it is inherently “electronic marshaling” because you can add I/O points without changing wires at the DCS, and you can put mixed signals on same comm link, and even better, ALL you have at the DCS is the comm wiring — NOT a pair for every signal.
      — less important because 4-20ma HART works pretty well, but still important is that the A/D and D/A conversions occur in the instrument rather than at the DCS. So just like HDTV, you get the whole signal without ANY added noise or you get none of it.

  2. Peter Ward says:

    This was a good piece.
    I have found it a lot of instrument people only when bothered go to the net to find information. Most hate FF as this requires brain cells to understand. Yes it has been a horror system to implement, if you think of it as HART and 4-20mA. It is a transmitter that has 2 wires and connects somehow to the control system. Therefore it MUST run like the rest.
    Enter the person who has read the manual, looked at the equipment, asked the questions, and low and behold, the system works. HART is a fantastic system, FF may be the way of the future. What has surprised me was the fact no one used a battery, Ethernet and optics. I thought this would have happened at least a decade ago. Ultra fast speeds and battery pending can be made Ex friendly worldwide.
    I digress.
    I am yet to see the H2 Ethernet system, and am looking forward to it. FF astounded me when saw what you ould pull out of a pressure transmitter. HART and Emerson AMS staggered me about 10 plus years ago. I was asked by one collage what all the fuss was about, why bother with AMS… Stunned. With one software package, and as put above with HART pass-through, you can document EVERY HART instrument on site, and THEN with Plantweb, monitor the lot and see is there are problems, nip them in the bud before they become a problem. EG blocked impulse line on a DP flowmeter. How many weeks or months can go by with this problem, it takes an astute operator to pick it up.
    Well lets see if this gets a response…. Cheers for the rant.

    • Jonas Berge says:

      I personally think Dan explained it well above. Digital comes natural to some but not all. For example, downloading DD files to integrate HART, fieldbus, and PROFIBUS devices into a system is not that different from downloading songs and apps from iTunes.

      The plant experience with FF varies greatly depending on the system used. Some DCS were introduced with FF but without any support by intelligent device management (IDM) software. They didn’t provide IDM support until 2010. On the other hand, DeltaV has had IDM software since the very beginning of fieldbus.

      Some early FF projects were over-engineered with segment calculation for each individual bus instead of doing just a few worst case ‘typicals’ which is the standard practice today. Perhaps this was because FISCO and high power/energy trunk (HPT) barriers were not yet available back then. In the past we were also not yet as confident with fieldbus as we are today so we didn’t put as many loops per bus as we do now. Today implementation is a lot simpler.

      Both the Fieldbus Foundation and Emerson have responded, and have spent the past few years improving usability.

      Enhancements to the fieldbus standard includes error free download meaning download once without retries, Electronic Device Description Language (EDDL with device level methods and views enabling task-based graphical device pages with user guidance instead of cryptic parameters scattered across blocks. NAMUR NE107 status signals for easy to understand device diagnostic alarm rationalization and routing. Backwards compatibility (COMPATIBILITY_REV) to make it easy to replace an old device with a newer version without loading new DD file or touching the system. And these enhancements continue making the work easier for the designers as well as the run & maintain organization:

      DeltaV has been improved greatly over versions 9, 10, 11, and 12 with many new enhancements that make fieldbus easy to use. For example, version 9 (2006) function blocks in the H1 card for complex time-synchronized loops, greater function block capacity, enhanced EDDL (graphical device display); version 10 (2008) device replacement and commissioning (using only a screwdriver without touching software like 4-20 mA), and express download, and HPR 61a registration; version 11 (2010) integrated power in the H1 Card (eliminating the marshalling cabinet), EDDL device level access (dashboards), and HPR61b registration; version 12 (2013) NAMUR NE107 (prioritized device diagnostic alarms) and DD Update Manager (automatic DD download keeping the system up to date without manual DD downloads)

      Emerson field devices are being released one by one conforming to fieldbus device profile version 6 (“ITK6”)

      The Fieldbus Foundation is just embarking on a second wave of enhancements have been announced known as “Project Gemstone”

      I personally agree that FF is the way of the future. All-digital; just like digital audio, digital photography, digital telephony, digital mail, digital television, digital video games, digital books, digital movies, digital payment, digital address book, digital maps, and even digital music instruments.

      Fieldbus takes the place not only of 4-20 mA signals but also of on/off signals, so you can pull out astounding diagnostics not only from pressure transmitters but from all devices including on/off devices such as on/off valves and electric actuators etc.

      Many plants did not know how to incorporate device diagnostics from their 4-20 mA/HART, FF, and PROFIBUS devices into daily maintenance and turnaround planning. However, now there is guidance in how to deploy intelligent device management (IDM) software and rewrite the work processes:
      The ISA108 group is also doing work in this area

      Today with FF and PROFIBUS you can monitor diagnostics not only in instruments, but also gas chromatographs, electric actuators / motor operated valves (MOV), tank gauging systems, variable speed drives, and motor starters etc.

      PlantWeb Alerts was indeed a breakthrough technology. It has now evolved into the NAMUR NE107 standard:

  3. Dear all
    I want to understand
    My 475 Field communicator has 3.9 Revision when I powerd it

    But on my Manuels of DVC6200 setup menu I read HART5 and HART7

    What mean’s that

    Hart5 is a revision of 475 Field communicator?

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