HART Tri-Loop & DVC6000s


Thread Starter

Bath, Andray AC

We have a DVC6020 positioner be used on a "combustion air" damper with a single piston actuator. We are using a Tri-Loop (HART converter) to provide position feedback from the DVC6020 positioner to our Yokogawa Centum CS DCS.
We are having an intermittent problem with the position feedback. The position feedback signal provided by the Tri-Loop deviates erratically and
without warning. 90% of the time the system works well, but intermittently we get these deviations. Has anyone experienced this sort of problem before? (The DVC6020s are a Fisher product normally used to quarter-turn control valve actuators. We have adapted the actuator to be used with this positioner)
Any help on this frustrating problem would be greatly appreciated.

Malcom Esquire

From what I can see, you are using the Hart protocole in a closed-loop control application where as it was initially intended for configuration and programming (which are intermittent by nature).
The information added to the 4-20mA current loop (e.g.: combustion air damper positioner feedback) are high-frequency and as such, very sensitive to ambiant electromagnetic noise.

My recommendations would be the following:

1. try to ground the 4-20mA signal shield at the voltage generating end, and only there. This 24VDC is produced either in the DCS or the DCV or somewhere in between, junction box or something. It would be a separate 24Vcc power supply then).

2. Run the cable in a metal conduit. (Not always practical in an existing installation)

3. (My personal favorite): You must have another 4-20mA signal available on the DCV6020 electronics which maps the position feedback. Connect this to the DCS instead of relying on Hart, and reconfigure the DCS to take this into account.

good luck,

Malcom Esq, P.Eng.
I would suggest you contact either your local Fisher representative or call Fisher direct at 641-754-3011 (USA). This is a known problem and there is a solution.
Is this a problem with the positioner feedback mechanism or with the hart converter...

I mean are there potentiometers which loose contact when the damper actuates or is there a problem in further electronics or in the Hart cable to the DCS.

Many times, the position feedback may use a potentiometer and which may loose contact once in a while and u can get an erratic signal. If the
erratic signal happens at the same positions (say between 40 nd 45%) the u may have a sensor problem.

If it happens erratically then u have either an electronics problem or communication cabling problem.

Looking at the positions and the problem zones over a period of time should help you in troubleshooting.

We have thought of problems with the feedback potentiometer. We have tried (unsucessfully) simulating the fault at the position that the damper normally operates at. The problem is not related to vibration as when the output to the positioner (DVC6020) is steady (e.g. 12.37mA) the position feedback via HART is also steady. This has been thoroughly tested as the positioner controller is put into "manual" when the fault occurs.

I have contacted Fisher in Marshall Town USA as one of the other contributors have suggested. (Thanks for your input). However, this is a different problem. The recognised problem showed behaviour where the signal from the Tri-loop would toggle between full scale and zero scale. The behaviour that we are experiencing shows the signal jumping by approximately 10 to 35%. The signal never goes outside the 4-20mA range.

I am not sure if the problem lies in the positioner (DVC6020) or the HART Tri-loop converter.

Still frustrated. Does anyone have a clue?
Thank you for your response. After contacting this phone number we tracked down the problem and a potential solution. Apparently the solution is to upgrade the firmware for the field device to revision 4. The only problem is that it seems it is not possible (yet) to buy the ValveLink software with the functionality to upgrade to firmware revision 4. Has anyone elese been able to gain access to this software???
Try to install a HART FILTER, this have been helpfull for us. We have solved a similar problem with that solution.
I am experiencing the same problem. I clipped in an amp meter to confirm, replaced the triloop 333U, rechecked config of DVC6010 & 333U, still not sure. I am suspecting the protocol.
The problem that we were experiencing was a problem with the update of the internal memory address in the DVC6000. The memory address dould only partially update before sending the signal via HART communication. When the position got close to 0FFFFFFFFF (hex) and was about to change to 1000000000 (hex) it would partially update (e.g. 1FFFFFF000). This position corresponded to approximately 32% (or 68% if reversed). Solution was to upgrade the DVC6000 firmware.
You should try out a Masoneilan SVI-2AP Digital Positioner as Chevron Refinery at Burnaby, BC, Canada.

Masoneilan SVI-2AP has an optional integral feature which provides 4-20mA valve position output and 2 limit switches.

Fisher representative had recommended HART Tri-Loop to Chevron, but their project coordinator felt the Masoneilan SVI-2AP is superior to that external set-up and also would avoid any possible unforeseen problem.

These Masoneilan SVI-2AP's had been running for about 2 years without any problem. They were supplied with exact mounting kit to fit FieldQ actuators in various sizes.
DO NOT WASTE YOUR MONEY! Valvelink is a total failure. We wasted tens of thousands on equipment and support, and it still not functional, and the manufacturer is giving up on us as well.