Two different issues, Corey. The clock isn't wobbling. It's just that the granularity on loading measurements is the granularity of the clock. We can't tell if the machine is busy for those 20ms or idle hence the error. The clock runs on schedule, the BPCs are predictable, but the STATION block cannot see how full a 20ms interval is. In 500ms system, a 20ms interval is only 4% error, but it is 10% of a 200ms interval and that is a big difference. Make sense? Alex Johnson Invensys Systems, Inc. 10707 Haddington Houston, TX 77043 713.722.2859 (office) 713.722.2700 (switchboard) 713.932.0222 (fax) ajohnson@xxxxxxxxxxx For the latest information on ArchestrA, go to www.invensys.com/Archestra.html. -----Original Message----- From: Corey R Clingo [mailto:clingoc@xxxxxxxxxxxxx] Sent: Wednesday, June 25, 2003 2:04 PM To: foxboro@xxxxxxxxxxxxx Subject: Re: [foxboro] CPU loading Accuracy in STATION block (was CP Load ) Yes, but it raises an interesting point: does control block processing also have a 20 ms jitter (20%) when the BPC is 0.1 s? Or is the control timing done by a different mechanism? Corey Clingo BASF Corp. |---------+----------------------------> | | "Johnson, Alex | | | (Foxboro)" | | | <ajohnson@Foxboro| | | .com> | | | Sent by: | | | foxboro-bounce@fr| | | eelists.org | | | | | | | | | 06/25/2003 12:23 | | | PM | | | Please respond to| | | foxboro | | | | |---------+----------------------------> >--------------------------------------------------------------------------- ---------------------------------------------------| | | | To: foxboro | | cc: | | Subject: Re: [foxboro] CPU loading Accuracy in STATION block (was CP Load ) | >--------------------------------------------------------------------------- ---------------------------------------------------| All, I have learned from a highly placed source inside the company that due to the resolution of the real-time clock (20 ms), the accuracy of each loading calculation is as follows: BPC Max. Error Usefulness 0.1 s 20.0 % not very 0.2 s 10.0 % marginal 0.5 s 4.0 % OK 1.0 s 2.0 % OK 2.0 s 1.0 % OK Thus, it is not that the STATION block does not work at faster BPCs, but that the measurement accuracy degrades substantially when the BPC is less than 0.5s (500ms). Does this make sense? Regards Alex Johnson Invensys Systems, Inc. 10707 Haddington Houston, TX 77043 713.722.2859 (office) 713.722.2700 (switchboard) 713.932.0222 (fax) ajohnson@xxxxxxxxxxx For the latest information on ArchestrA, go to www.invensys.com/Archestra.html. _______________________________________________________________________ This mailing list is neither sponsored nor endorsed by Invensys Process Systems (formerly The Foxboro Company). Use the info you obtain here at your own risks. Read http://www.thecassandraproject.org/disclaimer.html foxboro mailing list: http://www.freelists.org/list/foxboro to subscribe: mailto:foxboro-request@xxxxxxxxxxxxx?subject=join to unsubscribe: mailto:foxboro-request@xxxxxxxxxxxxx?subject=leave _______________________________________________________________________ This mailing list is neither sponsored nor endorsed by Invensys Process Systems (formerly The Foxboro Company). Use the info you obtain here at your own risks. Read http://www.thecassandraproject.org/disclaimer.html foxboro mailing list: http://www.freelists.org/list/foxboro to subscribe: mailto:foxboro-request@xxxxxxxxxxxxx?subject=join to unsubscribe: mailto:foxboro-request@xxxxxxxxxxxxx?subject=leave