roc364,
What I have done before is to set up 12 PLC memory locations. Then I save a reading every 5 minutes for a 1-hour "rolling" average. At the end of 1-hour, I drop the oldest reading and add the newest one. I sum all twelve and divide by twelve. Before the first hour has passed, I only divide by the number of readings taken so far. In your case you could create a 6-hour rolling average by using 72 memory storage locations. This method works for data that is not changing very much. If your data is changing rapidly, you will need to shorten the averaging cycle time, say from 5 minutes to 1 minute. However, the more data, the slower your PLC will be--the scan time will increse proportionaly.
As for RS-Trendx, if a program doesn't have a specific funciton built into it when it was written, then there is not much you as a user can do, except talk to Rockwell and ask them to add that function in the next software revision.
