DH+ monitoring/troubleshooting


Thread Starter

Jett, Darin

Hi all,
Are there any programs available for monitoring DH+ activity or troubleshooting slow networks other than unplugging one node at a time?

I have one DH+ network that normally runs fine with quick access (using RSLogix as my indicator) but occassionally slows down such as today. I'm currently down to about 1 update/sec in RSLogix and that is hard to work with.

The network is properly terminated at both ends, daisy-chained, running at 56K with 3 SLC5/04's, 2 RSView stations (with ~250 tags each and scan rates dispersed quite well), and 3 other RSLinx
stations for my computer and the logging apps.

Thanks for any tips/help.
Darin Jett

Greg Meister

Some of the best DH+ diagnostics software I've seen comes packaged with the SST 5136-SD card. I don't suppose any of your RSLinx stations have one of these cards in it? If not, it may be
worth considering one for your computer. You can find out more at http://www.mySST.com .

Greg Meister
NAC Northern Automation Controls Inc.
[email protected]

Kirk S. Hegwood

Mr. Jett,
We've found that the number of nodes, baud rate and distance are normally the problem with update time. Have you tried lowering the baud rate? That's what we've had to do with several projects. The more technical people on this list may have some calculations you could use.

Good luck,

Kirk S. Hegwood
Signing for Hegwood Electric Service, Inc.
[email protected]
You could limit your max packets to a lower number, this would decrease the amount of information on your network at any one time.
(Done in the topic configuration menu)


Dave Ferguson

I have spent a significant amount of time exploring this issue.

How well are your HMI's optimized. For instance, alarms and trends are being accessed at all times as well as possibly VBA applications.

By optimized I have repaired many vendor HMI'S that were gathering data from all over the place (PLC data tables). I will only speak concerning PLC 5's and anyone can note if there are differences in slc's.

When data is gathered via DH+

1. Each different PLC that you access creates a packet
2. Each data table that you access creates a packet
3. Data within 100 words create a packet. (Note timers/counters are 3 words each so each 33 timer and counter is a packet)

So if you gather from PLC1 data from N11:0, N12:0 and N11:100 and from PLC2 N7:0-N7:50 you created 4 packets right off, 1 for N11:0, 1 for N12:0, 1 for N11:100 (0-99=1 word) and 1 for the second PLC single word.

So if you have alarms all over the data table or trends, then you have what I call background noise of many packets all the time. This data is
gathered all the time when your HMI runs.

Now each screen you access may gather data differently so if you access many different data tables in your processor you will vary how
many packets are gathered on each screen + the background noise. If I have a screen that has 15 packets plus 10 packets of background noise, then I am getting 25 packets at the poll rate.

You could have a screen that has tons of packets because they are being gathered all over the PLC.

This is the reason to "data concentrate" all of the data to the HMI screens into very few data tables. I usually use an Integer register and a floating point and do file moves or individual moves or bit moves if it is scrambled enough.

The old Advisor MMI which became Controlview DOS and the Windows and then RSView had a tool to do traffic analysis. Now there is a tool in RSLinx to see DDE optimizations and I beleive OPC optimization but not native mode tags. E-mail me and I can expand on this further.

Dave Ferguson
Blandin Paper Company
DAVCO Automation
[email protected]

Steve DiGrazia

I was wondering if you've found a way to watch the traffic levels(volume) over the data highway. I think the bandwidth of the Data Highway is too small for the information we exchange from all of the nodes. I'm looking for a way to test, any ideas?