PanelView 550 Problem

Tom Jenkins

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Apr 2002
Location
Milwaukee, WI
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We have an application using DH-485 communications. There are six MicroLogix 1200's, each associated with one of six PanelView 550's, a separate seventh panel with one SLC 5/03, and an eighth panel with one SLC 5/04 and one PanelView Plus. The 5/04 is the "master" and initiates all PLC to PLC data exchanges. We are using a separate AIC+ for each device.

When the PanelView 550's are not plugged in the network it is fine. As soon as any of the PanelView 550's are plugged in, the network dies. This is NOT a cabling problem, since the PanelViews communicate just fine with the individual MicroLogix 1200's through the two AIC+ modules when the master comm link is disabled. We have exhausted all of the "quick fixes" and tough choices from our local tech support, and we are getting desparate (not to mention pretty pi$$ed off - I told the customer at the beginning of the project I didn't want to use PanelViews).

We are considering converting the existing ML-1200's with a single com port to new ML-1200's with dual com ports and dedicate the second comm port to the PanelView 550. However, the second comm port will only communicate DF-1 19.2 kbaud. The Existing PanelView 550's will only communicate using DH-485.

A) Does anybody know of a DH-485 to DF1 converter? This would save replacing the PanelViews.

B) Does anyone have a more cost effective solution to this dilemna?
 
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Too much traffic??

Perhaps all the tags in the PV's are scanning at maximum rate. Default rate when creating tags is '1' - the fastest. Rate can be set from 1 to 9, 9 being slowest. I have no idea what the actual rates are, but this might be worth investigating.
 
Tom, the system you have should work, but if you wish to use DF1 comms it is possible to flash a DF1 to DH485 and the reverse. If you search the archives here you will find some info on it. It is not a recommended Rockwell procedure but I have successfully flashed a PV1000 232 DF1 to a DH485 and it is still running happily 18 months later. Regards Alan Case
 
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Alan Case said:
Tom, the system you have should work, but if you wish to use DF1 comms it is possible to flash a DF1 to DH485 and the reverse. If you search the archives here you will find some info on it. It is not a recommended Rockwell procedure but I have successfully flashed a PV1000 232 DF1 to a DH485 and it is stilll running happily 18 months later. Regards Alan Case

Alan: we were told this system should work during design, as well. Unfortunately, reality and theory are in significant conflict! I assume this is the thread you reference: http://www.plctalk.net/qanda/showthread.php?s=&threadid=1759&highlight=flash+DF1

It will take me a day or so to digest it, but it looks like it might do the trick.

Mickey - the DataLink looks interesting - we will check them out too.

Gerry - we have tried changing PLC scan rates, with no success. Note that the PanelView 550 scan rate cannot be adjusted, at least both as far as we could find and per our distributor's (quite good) tech support.
 
Thats the thread. I may not be correct in the next part. Re reading the thread you need to have the PV with the 9 pin 232 style port not the RJ45 style port. If you do have this model then it is swappable on comms protocols. Regards Alan Case
 
Tom you say you have a master controlling PLC to PLC comms.
Does that mean you are using the msg instruction to read data from each ML1200 into the master then MSG write out to each ML1200 with that data.
Regards Alan Case
 
I had a very similar situation recently, except I was dealing with 26 nodes, each with a PV300 and Micrologix 1200.

We quickly realized that DH485 could support a max of 5-6 high traffic devices (PLCs/Panelviews)

In my case, I had to have all of the PLCs communicating to a PC running RSView SE. I also needed the PLCs to message information directly between one another.

What we ended up doing was switching the entire network from DH485 to Ethernet. We replaced the AIC modules with Digi-One IA realport device servers. www.digi.com
The digi modules have two serial ports (set up for DF1) and an ethernet port.

Digi has recently added support for DF1 tunneling over the ethernet network so that messages can be passed from one PLC to another, using the DF1 Message command. We were one of the first to test this, and it worked with very little trouble)

We did have to reflash the panelviews to DF1 as a few people have mentioned.
 
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There's a reason they call DH-485 "Data Sidewalk" ! Although it can reliably transmit messages between up to 31 nodes, it's often overloaded with half that many nodes, or even a handful of "high bandwidth" devices like PanelViews.

We're assuming that by "the network dies" you mean that timeout errors occur in other traffic on the network, specifically MSG instructions in the SLC.

I like jimbo3123's idea of using DF1 full duplex bridged across another network. I'd do the same thing with DeviceNet and 1761-NET-DNI modules if I were designing such a thing from scratch.

The first goal, though, should be to try to optimize the system as-is.

First, set all the DH485 node addresses contiguous to each other. Next, set the "Maximum Node" vale for each device to the highest node number on the network.

Then investigate a little-known PanelBuilder feature called "Update Frequency". You need to turn on visibility of the Extended Attributes (under the View menu in the Tag Editor) to see that parameter.

There's some information in the Knowledgebase about PanelView Standard update rates that is better than the Help file:

Knowbase G16029
 
Post the exact part number of your PanelView 550 to be certain about whether or not it can be converted to DF1 protocol. I suspect that it's the proper RS-232 hardware because you mentioned "AIC+" interfaces and not "1747-AIC" interfaces to the MicroLogix 1200 controllers.

If the PV550's can be converted, then you can use them with 1200R or MicroLogix 1500 LRP controllers, or with Ethernet or DeviceNet encapsulating devices like the Digi boxes or Net-DNIs.
 
Panelview adresses

Another thing to do to optimise panelview communications is to use contiguous blocks of addresses. The panelview will get a different packet for each address block (for RS232 this is 40 words) so if your panelview is looking all over for different PLC addresses then it will use a seperate packet for each address.

i.e N7:0 to N7:39 is one packet but N7:0 and N7:2 are two packets.

I transfer all of the program data into dedicated data files for panelview communications, this keeps the PLC-PV communication to a minimum.
 
Thanks to all for your help. We have implemented some of the suggestions (contiguous blocks of data and so on) already, but there are many of these suggestions that we can try. Ceratinly re-flashing the comm link to DF1 is appealing. I'll check the exact part number and let you know. The project is in Idaho, and we are in Milwaukee, so it will be a few weeks before we can check out the options. I will certainly let you guys know the outcome.

And, to answer Alan's question, yes, we use one read and one write MSG in the master SLC to get process data from and write commands to the 1200's and the other SLC. We've used this architecture successfully in the past, but not with PanelViews.
 
More info

I just talked to Tim. He infomred me that he did change the update rate on three of the PanelView 550s - 200 tags on each of three PanelViews. With only these three of the six total PanelView 550s pluged in, and with all the PLCs plugged in, the DH-485 comm link still crashed.

When I say the comm link "died" I mean the message instructions on the SLC master all showed errors continuously, and no data exchange occurred. I don't know if the errors were time outs or not.

The sticker on the PanelViews identify them as part CAT # 2711-T5A5L1
 
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Tom,

I hate to say it, but I think you're really in a pickle. I've been here with DH+. I would've expected to "update frequency" to work.

Here are some thoughts, though:

1) Going to a second port (as you suggested) might work, assuming you can network the PLCs on DF-1. I don't know if you can set unique addresses on that port.

2) DH-485 is RS-485 (of course), so you might try something totally wild: use RS-485 isolators with a transmit enable (you might already have them installed). You could "schedule" periods where each Micrologix/Panelview pair is available to the master. That should reduce the traffic on the network. You're not looking to get data every millisecond, so you could set up some good-sized time slices. I realize that this would be different than your usual communication routines, but desperate times... The ladder logic will, of course, be interesting but not too difficult.

Good luck!

AK
 
STRANGE BUT TRUE!

Our local A-B distributor kept pounding on this one, and he finally found a guy at A-B with an answer. Apparently it is NOT a good idea to use the standard Allen Bradley manufactured (and I believe recommended) cable for an application like ours. The power connection on either the AIC+ or the PanelView is connected through this cable, and this conection pulls down and the network.

We replaced one of the cables with a custom built, 2---2, 3---3, 5---5 with female DB-9 on both ends of the cable. Our test cable was installed by the contractor today, and the network is still up and running.

We will get five more like this out there and final test, but it looks like this one is solved!

Thanks to all for their help.
 

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