Actually sampling theory, ie. Nyquist, says that you should sample at least twice as fast as the fastest frequency that is present in the data. Doing otherwise opens you up to the possiblity of aliasing. Care should be used when using sampled data for troubleshooting unless you are sure that the proper anti-aliasing has been done of the front end. Alan D. Weldon Sr. Process Control Engineer Hunt Refining Company -----Original Message----- From: Johnson, Alex (Foxboro) [mailto:ajohnson@xxxxxxxxxxx] Sent: Wednesday, December 11, 2002 8:48 AM To: foxboro@xxxxxxxxxxxxx Subject: Re: [foxboro] FOXAPI Configuration for Foxhistory Ver 2.0 The fastest_rsr value controls the period that is used by the OM in the remote station. The period controls how often the OM checks a list for changes. So, a 10s fastest_rsr will cause the CP to report changes on the list once every 10 seconds. The historian will record the value it receives based on the recording period of the point. Sampling theory says that you want to sample your data at least twice as often as you want to record it. If FoxHistory is recording data at 30s intervals a 10s fastest_rsr is appropriate. If you have FoxHistory configured to record values every 0.5s, obviously a 10s fastest_rsr is in appropriate. If you are really interested in recording spikes that last 2 seconds you would need to configure FoxHistory for 1 and should set the fastest_rsr to 0.5. (A case could be made for 2s in FoxHistory and 1.0 as fastest_rsr; it sort of depends on how important the problem is.) Also, please note, that the fastest_rsr setting applies to all FoxAPI using applications on the machine, e.g., APC packages and PI. You can also tune your change deltas so that insignificant changes are not reported. Regards, Alex Johnson Invensys 10707 Haddington Houston, TX 77063 713.722.2859 (office) 713.722.2700 (switchboard) 713.932.0222 (fax) ajohnson@xxxxxxxxxxx <mailto:ajohnson@xxxxxxxxxxx> For the latest information on ArchestrA, go to www.invensys.com/Archestra.html <http://www.invensys.com/divisions/Archestra.html> . -----Original Message----- From: F.Foxreseng@xxxxxxxxxxxxxxxx [SMTP:F.Foxreseng@xxxxxxxxxxxxxxxx] Sent: Tuesday, December 10, 2002 10:53 PM To: foxboro@xxxxxxxxxxxxx Subject: [foxboro] FOXAPI Configuration for Foxhistory Ver 2.0 Dear All We have IA series 4.3 System having three nodes. The nodebus traffic of two nodes are very high (800 Packets/Sec). We have Foxhistory Ver 2.0 having around 4000 points configured on each node. Now during analysis of nodebus traffic, I found that foxhistory is major contributor. I checked FOXAPI configuration as Foxapi is used by Foxhistory to get real time data.(What I understand). I found that in foxapi.cfg file ,fastest_rsr (read scan rate) is not configured so foxapi is reading all the points at 0.5 Sec regardless of foxhistory configuration. One more point ,In foxhistory all points have fast freq=20 Sec and Read delta as per process requirement. Now suppose I put fastest_rsr = 20 (10 Sec) ,Now FoxAPI update table at every 10 Sec for foxhistory points , * Will it affect foxhistory data collection ? * suppose one point change it's value more than define read delta in 2 Sec, will get updated in foxhistory ? * what other thing I have to do ? Because above exercise help me to reduce node bus traffic . If somebody know other way to reduce traffic,Please also suggest. Regards Foxboro System Engineer SASREF _______________________________________________________________________ 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 _______________________________________________________________________ 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