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DL-06 Modbus

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  • DL-06 Modbus

    A customer of ours is using a DL-06. We are using the on board modbus port to communicate with 4 VFDs (AC Tech). They recently relocated the system to another part of their building. Also - they fried one of the VFDs and got a replacement. It is unclear whether or not the vfd was damaged before or after the move. Reguardless - now we get very spotty communication to those VFDs. It is acting like the port is being bogged down somehow and drops commands. Nothing has changed in the programming, and I have been on the phone with them for hours going over wiring and settings. Is it possible that the VFD that got damaged could have somehow damaged port 2 on the DL-06? I am really scratching my head at this point. Does anyone have any ideas?



  • #2
    If one of the Modbus Slaves no longer exists, but the program still is trying to communicate with it, it could just be an issue in that the retries and timeout settings are kicking in, so it slows down the throughput of all the other "good" slaves.

    Another (worse) scenario could be that the interlocking logic between the multiple Modbus Mastering instructions assumes success and does not monitor the busy or error bits (e.g. using a timer to round-robin the master comms), causing issues. When everything works, everything works - but when 1 comm goes bad, they all tend to go bad.
    There are 10 kinds of people in this world, those who know binary, and those who do not.


    • #3
      it's possible... do you know what exactly happened to the drive?


      • #4
        We have a heat system that has eight Watlow heat controllers communicating over Modbus with a Ethernet/Modbus gateway. With this system we've had two primary Modbus issues.

        1. An apparent electrostatic charge (from demolding a large part) fried the Modbus chip in the gateway. With a magnifying glass you could actually see a small hole burned in the chip. (We found that the MB-GATEWAY from AD was a lot less susceptible to damage from this issue)
        2. A less understood Modbus issue with the Watlow controllers that sounds similar to what you describe. The communication gets bogged down to the point where it barely works. What we've found is that the Watlow controller where the Modbus link seems to still be working is usually the culprit. We've never figured out what's happening or why. We have about 100 of these and it only happens 1-2 times a year.