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DeltaV Modbus RTU - Dataset status (Uncertain, Reason Unknown)

Hi,

We are communicating with the gateway by using Modbus RTU. We are reading Input registers (30000+) and have matched the register values at DeltaV end, everthing looks good except the status of the values which is continuously 'Uncertain, Reason Unknown' for all values. If anyone has faced similar kind of problem, please share your experience.

Thanks 

• DeltaV Modbus RTU

Syed Zaidi

• 26 Jun 2020 4:40 PM
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8 Replies

• Akash KA

  

  • 6 Jul 2020 12:33 AM

  Hi All,
  
  I am also facing the same issue except for the fact that we are using Modbus RS485 Serial here. Somehow, the values are getting 'Uncertain, reason unknown status'.
  
  Regards,
  Akash

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• MPHymel

  

  • 6 Jul 2020 1:20 PM

  In reply to Akash KA:

  We have had things like this happen with different interfaces. We often try setting up the dataset to grab an address before and/or an address after the actual space you want to read. We have also tried different Modbus data type settings for similar data types.

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• Jason.Brumfield

  

  • 6 Jul 2020 10:22 PM

  If your datasets are setup including status and the sending system is not transmitting status, I have seen this error. I have also seen it if the comm settings don't match on both ends.

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• Akash KA

  

  • 6 Jul 2020 11:08 PM

  In reply to Jason.Brumfield:

  Thanks for your suggestions. But all datasets in delta V comes with status. I have configured delta v as slave and m2m device as master.

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• Michael Krispin

  

  • 7 Jul 2020 4:29 AM

  In reply to Akash KA:

  DeltaV Modbus as Slave? Since which DeltaV Version this can set? I know only that the serial card is always master. To connect two master devices, you need an interface between. Check out from Hilscher. I have good experience with that.
  How many nodes you drive from DeltaV? Redundant Bus? Speed? Timeout, retry counter, amount of register in one dataset, cable shield etc.
  Those information where helpful to get a better picture.
  In general can say, if everything is ok from hardware and software side, the status is good. I did a lot of modbus/rtu connection.

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• Akash KA

  

  • 7 Jul 2020 10:36 AM

  In reply to Michael Krispin:

  Yeah. Delta V serial card is used as Modbus slave and MTN router as master. Comm parameters are Baud rate:9600, data bits:8, stop bit:1, parity:none. Delta V version is 14.1. 30 registers are pulled from delta V. Timeout is 300ms. Modbus RS485 half duplex . Shield cable is connected to earth.
  
  We solved this issue. The issue was with the opto isolator inbetween delta V card and MTN router. We had to connect the D+ cable from delta V to D- of optoisolator and D- cable from delta V to D+ of optoisolator. In addition to that, there are 2 termination resistors in optoisolator. Just 1 termination resistor at the downstream end of optoisolator has to be ON.
  
  Switching the polarity at MTN router side(modbus master) didnt work. Switching the polarity at Optoisolator side + turning 1 termination resistor has solved this communication issue.

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• Syed Zaidi

  

  • 7 Jul 2020 2:27 PM

  In reply to Jason.Brumfield:

  Thanks Jason.

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• Syed Zaidi

  

  • 7 Jul 2020 2:46 PM

  In reply to Akash KA:

  Thanks Akash for sharing your experience

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