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A very interesting approach! Great story, Roy!

Brian, I understand that some Modbus/TCP<->Modbus/RTU device servers cache the Modbus/RTU responses, so I'm assuming that you are trying to detect whether you are getting good data or old cached data. Am I correct? If so, the DOIAP (Digi One IAP) (see www.digi.com) forwards each incoming...

Gayatri, 1. What make/model PLC are you working with?... and are you sure that the PLC you are using supports Modbus/UDP? Modbus/UDP is not an official standard, as far as I know, so I wouldn't assume that every PLC will support it. 2. Wireshark is a good program for monitoring master and...

Tan, If you have an Allen-Bradley PLC that communicates via DF1 or EtherNet/IP, that will work fine, also.

Tan, No, the EtherMeter doesn't have programmable logic for controlling a valve. But if you link it with a PLC via Modbus, the PLC could take care of the valve control. If you already have a PLC, then great... otherwise any inexpensive PLC with Modbus should do (eg Automation Direct DL-05).

Paul, For flow measurement, I would recommend two Sensus SR flow meters equipped with ICE registers. The 5/8" size is rated for 1 to 20 GPM, so it should be the right size for your application. Here is a link to the Sensus meter... http://na.sensus.com/Module/Catalog/File/water?id=24...

Ayman, My experience using butterfly valves to control flow is limited to water applications, but my first thought was along the lines of something that Jonas mentioned above... that flow-control is difficult when the butterfly valve is near to being fully-closed. So in those cases, we use...

How about a little 3" Modbus/RTU Master LCD/keypad connected to a Modbus/RTU slave 4-20mA output module? 4-20mA Output Module... ADAM-4021 or ADAM-4024: http://www.advantech.com/products/ADAM-4021/mod_1-2MLDDH.aspx 3" Modbus Master LCD/Keypad...

I'd also recommend plugging the GPRS modem into the same hub that I mentioned above... so that its LAN traffic will also be visible to Wireshark.

Since the problem is at the master, I'd suggest inserting a hub (an old switch) into your working network. Connect the master premium PLC and a PC/notebook to the hub and run Wireshark on the PC/notebook to snoop the Ethernet traffic to see what is happening. Wireshark has the ability to...

Angela, I have experience with a different option to solve your problem... I've used the Digi One IAP, which can convert back-and-forth between Modbus and Rockwell protocols (both serial and Ethernet). I've used them for applications in the field, and as components within test equipment on...

After the system stops communicating, can you get it to start working again by restarting the master?... or the slaves? Your answer will give the forum an idea of whether the problem relates to the device(s) reaching their limit of open sockets.

Count me among those who recommend an off-the-shelf solution. Dataforth (www.dataforth.com) makes several 4-20-->0-5V converter modules. One that I'm familiar with is the 8B32-01, but I believe they have other models, also. They have a very knowledgeable outside national sales engineer...

Ritika, First, before using your custom software to interrogate it, I would recommend that you try to talk to the ADAM-5000 device using the ADAM-4000/5000 utility (download from Advantech). This utility program features auto device discover, and it will help you find it (in case its...

outacontrolman, What make/model of meter are you using? Depending upon the make/model, you may be able to adapt it so as to collect Modbus serialized data (total and flow) from the meter rather than having to deal with pulse and milliamp signals.

Raj, I was not able to tell whether you need 3-phase or single-phase and whether this is for your own personal use or to be offered for sale. But there is a power metering device that already does all of what I understand you are looking for (Metering, Data Logging, Modbus, 100BaseT...

Miroslav, If your slaves (servers) support Modbus/UDP, then you could use Modbus/UDP as an alternative. Since UDP is an unconnected (no open sockets) protocol, you can eliminate the overhead of 15 open sockets. I don't think that Modbus/UDP is a formal standard, but many devices...

QVS.COM P/N CC342 : RJ45F to DB25M P/N CC343 : RJ45F to DB25F P/N CC438 : RJ45F to DB9M P/N CC439 : RJ45F to DB9F

Roy, that was my question, too. Regarding the protocol used by the DCS, 'Ethernet' just isn't enough information.

If you can load a different/simple ladder logic program into the c*logix (preferably an example program from AB), and if it runs OK for an extended period of time, then I'd start to get real suspicious that the problem is based in the logic that you have written.