Controllogix with SST Profibus card

Christoph

Member
Christoph
Join Date
Sep 2003
Location
Indiana
Posts
345
I have a tank farm, approx 20 tanks. These tanks each have a E&H PMP75 profibus sensor the sensors are on 2 nodes of profibus PA which comes from a P and F converter And a SST DP profibus card in a controllogix rack. that we use for ultimatley tank weight. 75 percent of the tanks weights are fluctuating
some by 5000 lbs some by 500 lbs and all at the same time
and the change is gradual and cyclic. I have had Turnkey in to verify the sensors and the profibus integrity and they say all is well there. Any ideas on what to look at next?? or what could be going on??
 
What makes you think that the Profibus and Control Logix has anything to do with this? Did you try using a current or voltage reference at the sensor to see if the signal steadies out. I would check the signal from the sensor first to make sure there is no noise. I would look at the sensor first to verify it is working correctly. If the sensor has a local read out of voltage or current output I would get a scope and look at that first.
 
The sensors are profibus not an analog signal but digital. Turnkey is Endress & Hausers factory sevice company, The sensors have been given a clean bill of health and so has the profibus network That they sit on.
 
We use what I thought was a very well thought out caculation I have a good team of 3 Engineers and they made the calcs for me and I can find no issue with them. Just strange how they all change at the same time.
 
Look at the data you already have.

What is different between the 75% that are giving cyclic readings and the 25% that are not?

Are all of the tanks the same? Is a tank that varies by 5000lbs any different than a tank that varies by 500lbs?

Wild, uninformed guess, sunrise and sunset is cyclic and gradual too. Any correlation?

Shawn
 
When I say cyclic it is on roughly a 24 hour cycle. There are differences in diameter but all tanks are the same height. The sensor is an inches of water column device. The tanks do have agitators but run constantly and at a very slow speed 8-RPM. The difference in data between stable tanks and the ones changing is just that. Stable ones are rock solid and don't vary and the ones with variation are all over the place.
 
Last edited:
Shawn, may have it with daily cycle. Do you monitor pressure in the tanks? A few degree in temp culd cause what you are seeif if the tanks are not vented.

If you could, one quick test would be to put a constant signal on one of the level instruments and see if holds....if it does you know the profibus is not the problem.
 
The tanks are vented to atmosphere. I think I will put 1 of the sensors in test mode and put out a constant value and see what happens!
 
Well I placed 1 of the sensors in test mode with a midrange ouput. I
tested it for 24 hours and it was rock solid stable. So now I am really stumped!
 
How the sensors are installed? I think this is indeed case of variating reference pressure (tanks air pressure is not same as sensors reference pressure).
 
Sensor is mounted to bottom of tank with an isolating ball valve, it hangs straight down and is the 4 bolt flange style.
tanks are vented to atmosphere. so there is no pressure building inside the tanks. At least I know this is not any kind of plc related issue.
 

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