DeltaV Ff communication problem

[bernouli]

I have a DeltaV system running ~70% Foundation Fieldbus. I had a question regarding diagnosing Ff segment communication problems. I have a segment that has been in service trouble free for several years. Recently I have been getting communication errors from all of the devices on the segment. The DeltaV diagnostic software clearly indicates that there is a segment problem with the missedviewscan, tokenpasstimeouts, etc. The wiring terminations are tight and appear to be good. I am assuming it is a device problem. The devices are Rosemount 3051 PTs and Fisher DVC5000’s. In the past I have de-powered 1 device at a time and checked the DeltaV diagnostic software to determine which one is incrementing the errors. Is there a better and easier way to find the problematic field device?

[rezabejd]

The first and easiest thing would be a physical inspection of the devices - if you haven't already done that. In the past when we've seen this, I'd estimate maybe 3oo4 we find a device with water in it. That is, we unscrew the cover and it pours out.

Do you have a Relcom FBT-6? When we see "low frequency noise" issues, it usually means a bad segment power conditioner. An oscilloscope would detect this as well, I think (low Hz sinusoid superimposed on the 31.25 KHz).

Maybe P+F will come out to your site and demonstrate their diagnostics for you. I think their software can filter by device / transaction and MAYBE that will lead you to the culprit. I would not necessarily classify that as "easy" though.

Please - let us know what you find and how you found it, if you don't mind.

John Rezabek
ISP Lima LLC

[aagostin]

The majority of problems (in my experience more than 80%) are related to installation problems: terminals not properly tightened, water inside devices, cable not properly grounded, etc.
Since your application was running for several years, you can do the following: take a MTL/RELCOM FBT-6, this fieldbus multimeter can provide you detailed information about your installation dows to device level. It is most easy to use, and since it is Ex ia IIC certified, can connect to any application, including potentially explosive areas Zone 1 or 0.
If it is a device problem, the FBT-6 will give you a high reading of retransmissions on this particular device. If it is a general problem (e.g. fieldbus terminator missing), it will give you high readings on all devices. You can contact my colleague Tom in USA at tgerrity@mtl-inst.com for assistance. One possible problem could also be the cable as such: cable resistance increased, shielding degraded, terminals corroded. Using the FBT-6 directly at the device will check whether sufficient voltage is available (at least 9V); if not, the whole segment can behave strange. Something you can also check with a "normal" multimeter.

[sachinsbendre]

Dear Bernouli,

The best way is to use P&F -Mobile advance diagnostic module in one the sites in india it has helped to zero in the problem & here it was again Eemrson system.

Best Regards

Sachin Bendre

[bernouli]

Update,

Purchased a Relcom FBT-6 to aid in troubleshooting. Found that there were high signals readings on all the devices, indicating a fieldbus terminator issue. We use MTL 5995 power conditioners which have dip switchs to enable/disable the terminator. Found that the terminator was turned off on the MTL. Once the terminator was turned on the device signal readings dropped down to the 800 range. Can not explain why it only recently began having intermitten failures, but I am sure that it has been that way since the install.

Chris

[tfanget]

Dear Bernouli,

MTL has designed a new fieldbus diagnostic module. Plugged into its carrier, this module continuously monitors the performance of eight fieldbus segments, providing information on the network health and capturing retransmissions between the fieldbus devices and the control system.

MTL has implemented all Relcom FBT-6 features in this module. This is a fieldbus foundation device and communicates with the host control system via the segment.

This product has been approved by Emerson.

http://www.easydeltav.com/keytechnologies/fieldbus/devicedownloads/manufacturer.asp?mfg=MTL+Instruments