Need Help About Profibus Network

HI THERE

IF I'M USING PROFIBUS NETWORK FOR SCADA AND IF I HAVE TO DECIDE BAUD RATE FOR COMMUNICATION. SO WHAT ARE THE POINT TO BE CONSIDERED WHILE CALCULATING NETWORK LOAD AND HOW BAND WIDTH IS CALCULATED

deshpande_anmol said:

HI THERE

IF I'M USING PROFIBUS NETWORK FOR SCADA AND IF I HAVE TO DECIDE BAUD RATE FOR COMMUNICATION. SO WHAT ARE THE POINT TO BE CONSIDERED WHILE CALCULATING NETWORK LOAD AND HOW BAND WIDTH IS CALCULATED

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The length of network and slowest device will determine maximum baud rate. The number of devices on a segment is limited to 32. A repeater is required with more devices. As more devices are added to the scan list the scan interval will get longer but, Profibus DP usually updates MUCH faster than the control loop or the ability to process the data.

Yes, it is usually faster, but you should at least check the bus update time if the number of nodes approaches 50 or so.

I just worked on a project that had 85 nodes, and the I/O updates took 18ms. My scan time was 9ms, so my process image tables were lagging behind my scan. This is usually not even important, but I had several inputs that were only on for 25ms (I had no control over this), and I would miss them once in a while when the 18ms update and 9ms scan were out of synch just right. S7 gives you a ballpark time for the update by going to the Hardware Configuration, clicking on the ProfiBus network, and then clicking Properties>Network Settings>Bus Parameters.