Need array to hold data for Information Manager Calculations service

I am using PLC Connect to bring analyzer data in via modbus TCP/IP. I need to calculate a 24 hour rolling average for the data and believe using Information Manager server Calculation service is the only option to manipulate PLC Connect data. However I need to use an array so as to drop the first in value from the calculation when a new data point is captured. How can I access an array in 800xA that will persist between executions of the Calculation?

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dgriffin1 Rank: 4967

Asked 1 year ago

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I think for rolling average calculation you can use functions of Data Direct in Excel reading samples from Basic History. So all you need is to define Log Configuration for each monitored value and to create excel with using Data Direct Average function over defined time interval. Sure you can find some Data Direct examples in AKS forum.
If you need to use Calculations, try to use General properties aspect as a "external memory" for the Calculation.
Other options could be reading/writing values to text files (aka last century style) or to use external database through ODBC.

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by dgriffin1 Rank: 4967 on 5/6/2020 4:38:35 AM | Like (0) | Report

Thank you for the info. I am trying to keep the result available within the 800xA system for display via faceplate and alarming to the operators. I can use general properties, but even if only taking a sample every 5 minutes I am needing 288 variable values and a line of code in the calculation for each variable to determine if it is time to renew it. Makes for a very long code without an indexed variable. Sad to have the ability to use VBA, but no array available that retains the values from execution cycle to execution cycle. I may try accessing Excel as a data holder from within the calculation code.
In playing around with Calculation (did I mention this is my first time using Calculation) I also found that the Calculation service will not accept data values from MOD300 as input variables in my ver 5.1 system. PLC Direct and AC800M data seem to work fine, The values from all three sources show up in the online values column of the Calculation, but the MOD300 sourced values are treated as a zero value in the calculation. I can set the offline value to exactly what the online value is showing and set to use offline value in Calculation and the equation resolves correctly. Don't understand why because the MOD300 value is a VT-R4 datatype just like the AC800M value.

by kamil.herman Rank: 17 on 5/6/2020 5:29:49 AM | Like (0) | Report

I think using Calculations for average over longer period is Dead end.
I have another idea. What about to create hierarchical log in Log Configuration aspect using Aggregate option = Average over 24h period ? I never used that option, anyway it should work. Refer to manual 3BUF001092-610_A_en_System_800xA_Information_Management_Configuration.pdf at page 228.
You can display average result in Trend display then.
Regarding problem reading values from MOD300 likely it has something to do with scan time. MOD300 data pass through RTA board which is sensitive to scan intervals. I am not specialist for MOD300 but rather for AC450 . RTA of AC450 accepts scans 1, 3 and 9sec only.

by kamil.herman Rank: 17 on 5/7/2020 12:05:37 AM | Like (0) | Report

Next morning brings another idea. I am thinking about using Calculation output variable as string in record format like sample1#sample2#.... where # is delimiter between particular samples (or use any other rare character). Calculation output value is available for reading on next scan.
VBA offers powerful functions Split and Join. You can use Split in the beginning of the calculation to split the string record to an Array of samples. Build the string record from Array by Join function and store it to any output variable at the end of the calculation.
However length of string record may be several thousands chars. Here I am not sure what is the maximum string length of output variable. I don't find any limit in the manual.

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kamil.herman Rank: 17

Answered 1 year ago

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Need array to hold data for Information Manager Calculations service

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