PLC data monitoring

[riscoh]

Hi Guys, I need some advice on PLC data monitoring.... I have built a java based web application to monitor registers on a Modicon TSX Micro PLC. Jamod API is used to communicate with the PLC. The application is up and running for a couple of months and ran as expected. Currently the program would query the PLC every 20sec(live mode) and every 3 minutes for historical data. And the program would also query multiple times for some of the registers are far apart. ex. %MW600 - %MW680 and MW%700 - %MW750 My questions are: 1. Would it be better to just query like %MW0 TO maximum WORD and let the program select which words needs to be monitored? 2. Can this cause too much traffic that it affects communications between the PLC and the HMI(Magelis...)? 3. How often does a SCADA/HMI system communicate with the PLC? I mean time interval between grabbing information from the PLC? Thanks for your time and help...