composer 30 day rolling average

I was ask with the task in programming several 30-day rolling avereages. i figure the easiest way to complete this was using the MOAVG FC 165, how ever 30 days is to large for the FC. i was asking if anyone else has done this before and how??

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Cprice Rank: 1135

Asked 1 year ago

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Hi,
The MOVAVG block will average up to 255 samples, so for example, for a 30 day moving average you could configure 240 x 8 hour (28800 second) samples. For a better resolution you can cascade the MOVAVG blocks. A MOVAVG block with 240 x 2 minute (120 second) samples will give you an 8 hour moving average using 2 minute samples. Feed this into a MOVAVG of 240 x 8 hour samples and you have a 30 day moving average calculated from 2 minute sample data. Consider storing the data to restore blocks or possibly recipe blocks to avoid losing your your moving average in the event of controller failure / offline download. The restore block will load the moving average data set on power failure but will not tolerate an offline download. The recipe block will tolerate an offline download but will only capture the output of the MOVAVG block rather than the entire moving average data set. If the data is really important consider duplicating the MOVAVG logic in multiple nodes and then selecting the data from the node with the longest uptime or doing the calculation in a historian and writing back to the DCS.

Cheers,
Alan

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by Cprice Rank: 1135 on 7/24/2017 6:33:22 AM | Like (0) | Report

Thanks a lot Alan this is work much appreciated!

by Cprice Rank: 1135 on 7/24/2017 6:34:21 AM | Like (0) | Report

Thanks Alan this will work. Much appreciated!

by Cprice Rank: 1135 on 7/24/2017 8:36:02 AM | Like (0) | Report

Hey Alan, I do have a question. the second moving average block you said S2 would be 240 and S3 would be 28800. im assuming if you multiple those number together that would give the amount of time of your moving average in seconds. so if you multiply those number together that would give you an 80 day moving average. so if I would change the S2 from a 240 to a 90 that would give me a 30 day moving average?

by Alan Rank: 37 on 7/24/2017 12:36:01 PM | Like (0) | Report

Hi, Yes, you are correct. In my example I started out with a 3 hour and 30 day average and then changed to 8 hour without adjusting the samples of the 30 day average. Cheers,
Alan

by RickW Rank: 46 on 9/20/2018 10:50:42 AM | Like (0) | Report

A few things to understand: The sample interval of the final FC165 will determine how often the final moving average will update. The moving average is usually not set up to average all data points so it is an 'estimate' of the average.

by Cprice Rank: 1135 on 10/11/2018 9:45:42 AM | Like (0) | Report

if you wanted to save the data coming out of the FC165 but interlock it. to where you choose when to average and when not to average. would you use adapt blocks to increase Spec 3 or is there a better way?

by Alan Rank: 37 on 10/12/2018 2:57:52 AM | Like (0) | Report

Hi, adapting S3 with a large number will effectively halt sampling and the average calculation as well as retain the existing sample set used to calculate the average for later use. Whether or not the retained sample set is still valid for the new average calculation depends on what you are trying to achieve. Another way is to feed the output of the average block back into the input and put the average block into track. This loads the average block with the last average value, again this may or may not suit what you are trying to achieve.

Regards,
Alan

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Alan Rank: 37

Answered 1 year ago

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