Enable/ disable modbus Device


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I’m looking into the best way to disable a modbus device (multi-function power meter) to prevent timeout errors and data reading issues. Currently when a power meter is disconnected (circuit switched out) the data being pulled from other devices displays incorrectly. 

What I’m looking to do is condition a device being “enabled” by a digital input from the distributed I/O.  So effectively when a power meter is shut down it doesn’t effect any other data? Is this possible?


thanks. NHL

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First, a Modbus device that has is not connecting should not affect the data coming from other devices.  If it is, then you have other issues, probably related to Modbus IDs (are you using 0 or 255?).  Timeouts will affect other devices on the same Timing interval of the channels, but won't affect the actual number received from working devices, just how often it is able to poll.  This you can fix by putting each device on a different Timing / Offset setting.  But that only really works if each device is on its own serial port, or Ethernet IP.  If you are doing multidrop, then you are limited.

That all said, you can use the SetBypass() function to essentially disable a particular device, or a particular id on a device.  This is described in detail in 6.13 of the user's guide.  It can be used to disable a device, or to create a simulation when you are offline.

But, do take the time to figure out why one device's status affects the data being received by another device.  Simply bypassing the offending device is chasing the symptom and not the cure.  Once you figure this out, then you can implement the bypass to make your system run more efficiently.

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