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Not Communicating With Device, HART Diagnostics

Hello, 

I have a valve setup in the field on Analog Output Hart Card. 

I am getting intermittently ( approx every 15 minutes Not Communicating With Device) warning alarms, but the valve is still working (off the 4-20mA signal) and controlling.

1. From the HART Statistics screenshot, what does Timeout Errors mean?

2. Does the Not Communicating with Device warning mean I am losing the HART communication with the Device?

This is the 2nd AO card I placed the valve on and the same issue. The previous AO card was giving me I/O failure and the 4-20mA was loss so the valve will go to fail state. This also was intermittently. To get valve working again, we reset the power to valve. 

Also, I am unable to connect to device with AMS

Any ideas what could be causing this issue? Thank you

DCS Newbie

19 Replies

  • Kris Chandrashekar
    There is a possibility that the valve is the one that is creating the problem (HART communication issue). You can verify this be configuring the AO Channel to a 4-20 MA regular (HART not enabled) and watch for a day or two to see if the valve continues work without any issues. I am assuming that you had problems with 4-20 MA being lost with the previous AO card but now with the second AO card you are able to control the valve properly. This will verify that the problem is HART related and not 4-20 MA related.

    Another issue that existed some years ago:- If the control valve positioner is a Fisher FieldVue type (could be other manufacturers as well), the electronics in the positioner will go to "sleep" at say less than 18 volts DC (instead of the normal 24 Volts DC). So, in the AO output configuration if you set the 4-20 MA low and high limits to something like -10% and +110% then in the valve fully closed position the output could be something like 3.5 MA or less (instead of 4 MA) in which case the electronics could go to "sleep" and the valve will not function. Your screen shot shows the output to be at 48.05%. At that stage the electronics should be working fine. So, I am guessing that it may be a positioner related problem. But, just wanted to mention this as a possible issue.

    As a third possibility, if you have a spare positioner, replace the current positioner with a spare. Hopefully the problem should go away.

    Good Luck
  • DCS Newbie

    In reply to Kris Chandrashekar:

    Thank you Kris,

    After digging a bit deeper, I discovered we have multiple valves like this, Flowserve LGX3200MD, that had communication issues in the past and simply disable the HART and the valve work fine.

    If I disable the HART, what capabilities am I losing?

    Thank you
  • DCS Newbie

    In reply to DCS Newbie:

    Hello,

    One more thing. I attached the HART handheld communicator directly to the terminals of the positioner where the AO wires from the DeltaV is connected. I waited and notice no communication 3 times on the hand held communicator.

    Thank you
  • Kris Chandrashekar

    In reply to DCS Newbie:

    Depending on the manufacturer (Fisher, Samson, Flowserve etc.) various pieces of information are available via HART communication. Obviously the Primary Variable (4-20 MA) is common to all of them (Implied valve position or IVP). Second variable, third variable and the fourth variable would use the HART communication to send information back to DCS about Actual Valve position (AVP), Air Pressure in the actuator etc. One of the commonly used information would be the IVP and and AVP so that you can diagnose valve problems (for example your IVP is 48% -- i.e. you are asking the valve to go to 48% open where as the HART AVP coming back shows it to be 45%. This could be because of a stickly valve or not enough air pressure etc.). Useful diagnostic tool because if the IVP and AVP start to widen in their gap over a period of time, you know that the valve is continuing to deteriorate in its performance and hopefully you can schedule a repair/maintenance on it before it just fails without any warning. By using the HART information (AVP) you are getting an early warning. In the same way, if you have an AI channel (HART enabled), a Mass Flow transmitter could be sending Density as its secondary (HART) variable, temperature as the third variable and so on. Along with these analog HART information, various device alerts are also sent back to the DCS as HART discrete signals. It is up to the manufacturer to decide on which pieces of HART information are sent and on what variable number it is sent.

    HART variables are definitely useful pieces of information, but it requires good wiring practices and maintenance practices to make sure that they are continuing to work properly. When those pieces of information are not very critical, it is definitely O.K. to disable the HART capability and especially so when it starts of affect/interfere with the basic control functionality (4-20 MA control definitely needs to be working without any interference). In your case it looks like many of these Flowserve valves has disabled HART channels due to some of these issues. By the way, your case is not an exception. Over a period of time, many users run into the same issues and will just work with HART disabled channels.
  • DCS Newbie

    In reply to Kris Chandrashekar:

    Thank you so much Kris,

    Another disadvantage of disable HART is no communication to AMS.

    Can 4-20mA effect the HART and cause no communication alarms?

    If I disable the HART, then I am disabling the HARD device alarms, correct?

    Thanks
  • DCS Newbie

    In reply to Kris Chandrashekar:

    Kris Chandrashekar said:
    By the way, your case is not an exception. Over a period of time, many users run into the same issues and will just work with HART disabled channels.

    Could this because of noise or electromganetic interference around the valve in the field? Maybe certain HART devices are senstive the noise.

    Thank you

  • Kris Chandrashekar

    In reply to DCS Newbie:

    You are correct. Disabling HART will cause no communication with AMS. To the best of my knowledge HART can affect 4-20 MA but not the other way round (i.e. 4-20 MA does not cause HART related problems). Not having the AMS communication can be an issue with I/E technicians since they will have to go out into the field and physically connect to the Instrument with a Rosemount handheld 475 (or whatever) instead of having the ability to do most of the work from their shop (assuming the AMS station is located in their shop).

    4-20 MA wiring, how the shields are terminated, running DC wiring right next to AC wiring, Electromagnetic interference and other factors do contribute to the HART communication issues. There are times when wiring is perfectly fine but the electronics in the control valve positioner goes bad and replacing the positioner will resolve the issue. So, you have to make a decision on how much the HART variables are worth and then decide to either make sure everything is working right if they are critical or ignore and just work with a non-HART 4-20 MA channel.

    If you disable HART the I/O failure alarms (like IOF) should continue to work. So, you should get an IOF alarm on the DCS if there is a device failure because the 4-20 MA is no longer working/control functionality has been lost.
  • DCS Newbie

    In reply to Kris Chandrashekar:

    Can I hook a HART handheld communicator directly the positioner (without the AO wires connected) and wait for communication failuers between the handheld and positioner to occur? This will tell me if any positioner problems.

    Thanks
  • Kris Chandrashekar

    In reply to DCS Newbie:

    I think you mentioned about this earlier. See cut & paste from your earlier posting:-
    ------------------
    Hello,

    One more thing. I attached the HART handheld communicator directly to the terminals of the positioner where the AO wires from the DeltaV is connected. I waited and notice no communication 3 times on the hand held communicator.

    Thank you
    ------------------

    You can certainly try this again. The only issue with this is that the communication problem has to occur while you are watching the handheld communicator. If it does not occur for an hour or two, then you may run out of patience...!!!
  • DCS Newbie

    In reply to Kris Chandrashekar:

    Thank you Kris,

    The last time I hooked the handheld communicator to the positioner terminals the wires from the AO card was also connected and I saw the not communicating error on the handheld communicator. But i am not 100% sure if this error was due to AO wiring or the positioner.

    So this time I want to disconnect the AO wiring, and connect the handheld communicator to the positioner alone and wait for an error.

    Thanks,
  • Kris Chandrashekar

    In reply to DCS Newbie:

    O.K. I misunderstood. Yes. You can disconnect the AO wiring and try with the handheld communicator. You may have make arrangements to provide 24 Volts DC from another source to power the electronics in the positioner. (Since the AO wiring is disconnected the 24 Volts DC is no longer available to the control valve).
  • DCS Newbie

    In reply to DCS Newbie:

    Is the Timeout error I see in Hart Statics related to HART not communicating intermittently?

    Today, I will diable the HART, Reset the Stats for the channel in Diagnotics and see if that fix that issue for a few days. If that fix the issue, I know my problem is realted to the digital HART signal and I can inspect the wiring for any wiring (4-20 MA wiring, how the shields are terminated, running DC wiring right next to AC wiring, Electromagnetic interference , etc.) issues. I think this is a good start.

    What do you think of my plan to start?
  • DCS Newbie

    In reply to Kris Chandrashekar:

    Kris Chandrashekar said:
    (Since the AO wiring is disconnected the 24 Volts DC is no longer available to the control valve).

    Thank you. 

    Help me understand. So the DeltaV AO card is providing a 24V DC and 4-20mA to the control valve for power and control?

    Thank you

  • Kris Chandrashekar

    In reply to DCS Newbie:

    You can reset the stats in diagnostics. But you need to leave the HART enabled. That way diagnostics will continue to capture any updated time out errors. When you reset the stats everything should show zero. After some time if you see time out stats increasing, it means the valve is still failing to communicate HART intermittently. If HART is disabled, you will not see any updates in the HART statistics window. So, if you want to reset the HART stats, I would suggest leaving the channel as HART enabled and then watch the diagnostics for a few days to see if the timeout counter starts to increase again.

    Please refer to DeltaV books online and find the wiring diagram for AO cards. You will see that the +/- of the AO card are connected to the +/- of the load (control valve in this case). The AO card gets the 24 Volts from an external power supply. So, the AO card is the one that sends the needed DC power to the control valve. If you disconnect this, you need another power source to bring the 24 Volts to the control valve. Your Instrument shop should have these power sources (typically a small handheld unit with two cable leads made by Transmation or other manufaturer).
  • DCS Newbie

    In reply to Kris Chandrashekar:

    Thank you Kris for the help.

    I am renting an oscilloscope to monitor the signal and take some screenshots to report back here. I want to see if induced volatges is interfering with the HART signal causing no communication.

    Thank you

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