ABB AC500 CS31 bus failure

[grnick50]

Dear All,

I have build and HVAC control system for a big shoping mall, based on ABBs AC500 and using the CS31 bus.
The air handling units (AHUs) are split into two groups.
Each group has an AC500 PM573-ETH CPU and 7 RIOs (CI592) on CS31 bus.
Each CS31 network is about 600m so a repeater from phoenix contact was used in the middle of the bus. The cable used is a profibus cable and it is properly terminated at each end (R1->B1 & R2->B2). There are no VFDs around nor any other equipment that would produce electrical noise.

The system was commisioned (without the repeaters) and it seemed that all is ok but after a few days the client copmlained that the system is down. I visited the site and I read the errors from the PLC. The problem was that the PLC could not see the RIOs through the CS31 bus. On the RIO modules(CI592) the CS31 LED flashed indicating that the module is in diagnosis mode. The problem only went away after a power cycle of each RIO. I left and the system failed again after a week or so. At that point I thought that the problem was the bus length exceeding the mark of 500m. So today I went on site and installed the repeaters thinking that this was the root of the evil. The repeaters worked straight away without any issues. I left and then after a couple of hours I get a call from the client that the system cannot see two of the RIOs.
I asked him to reboot them and the problem went away.

In the past we did that 1000 times with Siemens & profibus and had no issues whatsoever. The ABB rep convinced us to give the AC500 a test drive but now it pays us back with hard time.
As you understund I am in the spot and at the moment I dont know what the problem may be. So any help is highly appreciated.

Regards Nik

 

[Friedrich]

Hi Nik

I'm not exactly familiar with the 500-series, but I use the 800-series on a regular basis.
The first thing I noticed is the amount of remote IO's you are using on a single bus. You should check if it's supported. I know from the 800-series that depending on the type of IO's (analog or digital) there's a restriction on how many of these you can use on a single bus/cluster modem.
From what I read in the manual; If you double click the "COMX_CS31_Bus" in the tree-view you should get a configuration window, with a diagnostics-tab telling you if there's too many IO's connected, and if the connected IO's sum up to a cycle time that exceeds the set limit of 65535ms.
Even if there's too many it won't stop you from downloading the project.

I can't find anything in the manual that explains what this "diagnostis mode" is, and why it enters this mode. Give ABB a call and ask.

If you find the problem, let us know!

Regards Friedrich

 

[grnick50]

Friedrich,

The Number of RIOs is checked against the limitations. I think that control builder will complain if you exceed that. The ABB rep is already planning a visit on site.

Where is the COMX_CS31_BUS? In Codesys?

Thanx

 

[Friedrich]

I thought you were using control builder plus. I don't know if CoDeSys has the function to check the configuration of the CS31-bus.
Open "PLC configuration" in the tree-view to the left. Then under "Interfaces" you should see the comports. Check if it has the same tool there.

Control builder plus manual: http://www05.abb.com/global/scot/sc...ffdc1257c2100539ee5/$file/3ADR025078M0203.ZIP

Check 2.4.2 if you want to see how it looks in control builder.
If you have control builder, and CoDeSys can't tell you if there's too many RIO's, make a new project and just add the cpu and RIO's in control builder and check there. Or even better, make ABB do it for you

This is just a hunch, but it's worth checking atleast.
Just remember that there's almost always some tinkering with stuff you use for the first time, so don't give up on ABB just yet.

 

[grnick50]

Friedrich,

I use control builder. I did the check you recommended and all is good. I am planning to go on site and double check terminations, earthing etc.

To be honest, I liked the 500 a lot and I also like Compact HMI 800. I think it is good value for money. The thing is that I believe that somethings are not explained very well.

For example:
The CS31 LED flashes on the CI592 modules, and in the manual says that this means that the module is in diagnosis mode.! Thats it! nothing about what it means and what is recommended to fix it!

 

[grnick50]

Sometimes you learn the solution to some problems the hard way and you would not wish this to happen to your worst enemy, so I post the solution to the problem.

For some reason I had set the PLC task to be freewheeling and not cyclic. Because of that the PLC had longer cycle times and CS31 did not like that. The task was changed to cyclic and all is good now. The bad thing is that IMO this was not well documented in the manuals and we were searching in the wrong direction (EMC, repeaters etc).

 

[Friedrich]

Nice to hear that you fixed it. If you learn the hard way, you tend not to make the same mistake twice
I agree with you from what I've seen regarding the 500-series documentation, they really need an extreme makeover and give it some depth of what the system is doing and why.