Best way to Communicate

OK! Where to start. I have several sites online with a DSL or Dial up close by I need to send the data from the PLC to my server from several states. I would like real time data but 2-3 minute updates will be fine. I have read about some HMI software companies that allow you to publish HTML files and send them. (is this a data stream or snap shots?) I also feel that HTML's file has tons of graphs and the file is quite large I will also need a PC at every site. I may be limited on the amount of data I can view at one time from some of the other sites.

Is it possible to send the data directly from the PLC across DSL or Dial up into the server, I will then put the HMI software on the server and write my graphic screens there to view several sites, data trend, alarm notification.


Will this work or do I have my head somewhere it doesn't belong!

Hello awilken;
We have used SCADA-based modem polling (we used Citect and Sixnet industrial modems in our projects, but you can probably adapt your own soft/hardware combination)with good results, especially since we allowed time-based polling of the PLCs from the SCADA, and emergency dial-up from the PLCs (that's where the autodial functions of the Sixnet modems came in handy).
We also have used Siemens CP343-1-IT Ethernet processors over the Internet; they host Java applets that allow you to configure the data you want to be available over the Ethernet link. Other manufacturers must have modules that do the same.
Hope this helps,
Daniel Chartier

How hard is it to set up this type of system? I am pretty new at this. I have a modbus controller that is going to send most of the data, some level switches and pressure switches.

Click to expand...

Hello, all;
awilken replied to my earlier post through a PM, but I feel everyone should be invited to help him out.

Now, the hard parts for the serial modem comms were of 2 levels:
1)determining the polling structure of the data (what data is needed, at what ratte to call them, how to interpret the data and bring it into the SCADA pages);

2)setting up a robust comm link through the modems, and determining the "Problem protocol": what to do when you cannot access the PLCs at specified time intervals (redial immediately, wait for the next polling sequence, generate alarms and warnings, etc...).

Once you have specified your working standards, generally ebverything falls into place. Of course the details of the comm links must allow for the specific SCADa package and comm link contriol you choose, and for the protocol you are using to exchange (Modbus RTU is different from ASCII, for example).


Hope this helps,
Daniel Chartier