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    Modbus Communication require enhance stability

    Hi all, I am having a system which using PLC to read 3 weighing indicators with Modbus.
    but some times the reading that is send from indicator seems like hanging and causing system to overweight.
    The reading hang is only happen to one of the indicator instead of all 3 together.
    the baud rate using now is 19200 and we are using shielded cable for Modbus communication.
    The total length of looping is not more than 2m.

    Is there any recommendation on how I can improve my system?

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    Re: Modbus Communication require enhance stability

    Hi,

    The first thing you should do is to debug your system....to find the cause of the problem.

    There is:
    * the sensor hardware
    * the sensor bus
    * the bus communication
    * the calculation within the microcontroller (several steps)
    * the output to the human interface

    But you don't give those details, thus we are not able to give detailed assistance.

    Klaus
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    Re: Modbus Communication require enhance stability

    Quote Originally Posted by KlausST View Post
    Hi,

    The first thing you should do is to debug your system....to find the cause of the problem.

    There is:
    * the sensor hardware
    * the sensor bus
    * the bus communication
    * the calculation within the microcontroller (several steps)
    * the output to the human interface

    But you don't give those details, thus we are not able to give detailed assistance.

    Klaus

    Hi Klaus, thanks for your prompt reply
    The sensor hardware and sensor bus that you mentioned is input of PLC?
    while for the calculation, my PLC is using instruction function to read the modbus, then convert the reading from decimal to hex.

    The current issue is that, in my PLC, i can see 3 indicators reading is running, while there is some times which the reading is stuck in PLC register even the indicator display is still running, this only happen to either 1 of the indicator at 1 time.

    there is no HMI in this system.

    - - - Updated - - -

    Quote Originally Posted by KlausST View Post
    Hi,

    The first thing you should do is to debug your system....to find the cause of the problem.

    There is:
    * the sensor hardware
    * the sensor bus
    * the bus communication
    * the calculation within the microcontroller (several steps)
    * the output to the human interface

    But you don't give those details, thus we are not able to give detailed assistance.

    Klaus
    Click image for larger version. 

Name:	Modbus.PNG 
Views:	5 
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ID:	154430


    This is how my connection looks like, the modbus wire is looping between indicator.



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    Re: Modbus Communication require enhance stability

    Quote Originally Posted by alpha91 View Post
    Hi all, I am having a system which using PLC to read 3 weighing indicators with Modbus.
    but some times the reading that is send from indicator seems like hanging and causing system to overweight.
    The reading hang is only happen to one of the indicator instead of all 3 together.
    the baud rate using now is 19200 and we are using shielded cable for Modbus communication.
    The total length of looping is not more than 2m.

    Is there any recommendation on how I can improve my system?
    Hello,

    did you declared exactly the same transmision parameters for three slaves?

    What Modbus function is your master using to get values of reading values? What memory addreses your slaves using for returned variables?
    One I can reccomend is to use "software Modbus master simulator" instead of your PLC.
    BTW: what model and vendor of PLC are you using?

    Kind regards



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