Latency in Modbus Devices


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I am reading multiple Modbus RTU devices through Modbus TCP on the DAQFactory system. I use devices that convert Modbus RTU to Modbus TCP, with each TCP device containing a maximum of 10 devices. I have around 60 devices in the system, and I read multiple register addresses of these devices. I should note that when I perform individual readings through DAQFactory and Modbus pool for all devices, I can see the data. However, when I try to read all devices through a single program, some data does not arrive initially, and the reading box displays a cross sign. After a few hours, these crosses disappear, and only the unit I specified is displayed. Furthermore, even after a few more hours, the refresh of the received data takes a considerable amount of time. I am looking forward to your response. Thank you in advance.

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This sounds to me like a hardware issue.  Personally I would never use a ModbusRTU -> TCP converter unless I needed to connect from a tool other than DAQFactory.  DAQFactory supports ModbusRTU over Ethernet so you can use a simple Serial->Ethernet converter and avoid the issues created by having a protocol translator in the middle.  If you do use a normal Serial->Ethernet converter, I recommend the ones from SeaLevel which have a "RAW" port you can connect to.  This port eliminates the need for any intermediary software or virtual comm port drivers.

So do you have 60 RTU devices connected to 6 TCP devices,  or 600 RTU devices connected to 60 TCP devices?  Are you seeing timeout errors?  Are you using Channels exclusively?  If you are using channels, you should set it up so that all the input channels on all the RTU devices connected to a single TCP device have the same Timing and Offset, and that ones connected to a different TCP device have a different Timing/Offset combination.  This will tell DAQFactory to query the TCP devices simultaneously.  Note that you should not use different timing parameters for RTU devices connected to the same TCP device as I would imagine that TCP device only supports one communication line at a time. 


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