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How to slow down the polling rate of an EIOC

Hello All,

I am dealing with an issue where I have an EIOC communicating with a ROC over a radio network and the EIOC is polling the ROC too fast for the radio network causing occasional communication issues. I was wondering if anyone knew how to slow down the polling rate of an EIOC. I have found no settings in the EIOC configuration that will allow me to control this.

I have already tried to add extra bogus LDTs to one of the PDTs I am having issues with, but this only increased the communication rate due to the EIOC sending extra messages trying to request register information that did not exist. ( I have been looking at the communication rate using wireshark to look at the packets being sent from the EIOC to my device and from my device back to the EIOC).

Any ideas or information anyone has about this would be greatly appreciated.

Mathias Whitworth

• 10 Jun 2020 3:33 PM
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7 Replies

• Lun.Raznik

  

  • 10 Jun 2020 3:54 PM

  What version of DeltaV? There was a version of DeltaV (EIOC) where scan rate was fixed. What is ROC?

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• Mathias Whitworth

  

  • 10 Jun 2020 7:12 PM

  In reply to Lun.Raznik:

  It is DeltaV 13.3.1. What version was it that the scan rate was fixed? A ROC is a Remote Operations Controller sold by Emerson. www.emerson.com/.../emerson-roc800-series

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• Andre Dicaire

  

  • 10 Jun 2020 7:43 PM

  In reply to Mathias Whitworth:

  The EIOC was released in v13.3.1 supporting Modbus TCP, EthernetIP and IEC61850 protocols. You must therefore be using Modbus TCP protocol.
  
  The configuration dialog asks for a Time out Period and a retry count. There is no setting for scan rate. The polling is sequential. The more LDT's there are, the longer it takes to gather their data.
  
  We do not know how long the EIOC waits after it receives a response before it sends the next poll. But if the TIme out is too short, the EIOC may send a retry too soon.
  
  Have you tried increasing the Time Out period and confirming that the EIOC is waiting for each response? If you are seeing the EIOC request before a response, this would indicate need to increase the Time Out.

  Andre Dicaire

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• Lun.Raznik

  

  • 10 Jun 2020 7:44 PM

  In reply to Mathias Whitworth:

  I am mistaken :(... I thought v14.3.1 EIOC would have polling rate settings.
  
  How about you create bogus PDT? I am guessing it is doing a round robbin poll of the devices.

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• JoshC

  

  • 10 Jun 2020 8:45 PM

  I have 14.3.1 EIOC running Modbus/TCP and there is no way to adjust polling rate that I've found. Mine is generating 300-400 messages a second for 6 devices (11 LDT's). Hopefully they will get this fixed and add a way to slow it down. I have issues too with servers (slaves) getting overwhelmed with all the polls.

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• Mathias Whitworth

  

  • 12 Jun 2020 8:32 PM

  In reply to Lun.Raznik:

  Thank you for the suggestion. I do not think this will help though because the polling rate for each PDT is independent of the other PDTs. The EIOC handles communications with each device separately so adding another device I do not think will help.

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• Mathias Whitworth

  

  • 12 Jun 2020 8:41 PM

  In reply to Andre Dicaire:

  Yes I am using Modbus TCP protocol. I was informed by one of my coworkers that when he talked with an application engineer from Emerson he was informed that the time out period parameter does not really work unfortunately.
  
  I did discover though that adding the extra LDTs did slow down the polling rate a little. I found that I was including some communications between the EIOC and ROC that I should not have when I was calculating my polling rate. I am going to try adding more LDTs to the PDT to see if this decreases the polling rate even further. I will let you know my results.

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