Average Value

MrCyrax · Oct 27, 2014

How would I average a reading in a M340 over a period of time?

I'm reading amps from a power meter but the reading I think is too erratic.
I would like to make it more stable change gradually.

GeoffC · Oct 27, 2014

Unity has 2 moving average function blocks available. One uses a fixed number of samples the other is a weighted average
Not sure of the function names I think the names start with MAV
If someone else doesn't jump in with the names I will post again tomorrow

MrCyrax · Oct 27, 2014

Thanks I looked for MAV* but nothing

Tom Jenkins · Oct 27, 2014

MrCyrax said:
How would I average a reading in a M340 over a period of time?

I'm reading amps from a power meter but the reading I think is too erratic.
I would like to make it more stable change gradually.

It sounds like you really want to implement digital filtering. Search for that term on this site and you'll get lots of results.

I usually use the method attached, and use a timer to implement periodically. The period varies with the process variable fluctuations, but starting at 0.3 seconds works well often. The number of readings to averages also varies, but 10 is a good place to start.

Note on the downside that the increased stability comes at the price of slower response.

Brendonh · Oct 27, 2014

GeoffC said:
Unity has 2 moving average function blocks available. One uses a fixed number of samples the other is a weighted average
Not sure of the function names I think the names start with MAV
If someone else doesn't jump in with the names I will post again tomorrow

AVGMV and AVGMV_K

Lare · Oct 27, 2014

Tom Jenkins said:
It sounds like you really want to implement digital filtering. Search for that term on this site and you'll get lots of results.

I usually use the method attached, and use a timer to implement periodically. The period varies with the process variable fluctuations, but starting at 0.3 seconds works well often. The number of readings to averages also varies, but 10 is a good place to start.

Note on the downside that the increased stability comes at the price of slower response.

Filtering methods have discussed many times, here is couple where code is converted to ladder which Tom mentioned:

http://www.plctalk.net/qanda/showthread.php?t=47235
http://www.plctalk.net/qanda/showthread.php?p=298656

MrCyrax · Oct 28, 2014

Tom Jenkins said:
It sounds like you really want to implement digital filtering. Search for that term on this site and you'll get lots of results.

I usually use the method attached, and use a timer to implement periodically. The period varies with the process variable fluctuations, but starting at 0.3 seconds works well often. The number of readings to averages also varies, but 10 is a good place to start.

Note on the downside that the increased stability comes at the price of slower response.

Thanks This is exactly what I need. Just need to figure out how.

Brendonh said:
AVGMV and AVGMV_K

Thanks

Brendonh · Oct 28, 2014

MrCyrax said:
Thanks This is exactly what I need. Just need to figure out how.

Thanks

Have a Read of the help file in unity for the avgmv block, it does exactly what Tom and Lare are describing and explains it in quite good detail.

Lare · Oct 28, 2014

Yeah, it is same function:

http://www.schneider-electric.cn/downloads//85257689000007EE/All/0F15DC90FEAAD05A852576B2006BB1B5/$File/12-Unity-EN.pdf

page 227

I have earlier programmed my own filter block for Unity fot this.

I could use avgmv block also, but then I would need int_to_real and real_to_int conversion in my program...

grnick50 · Oct 31, 2014

I dont know if you are using an AI to measure the amps but if yes then in the configuration of the analog card you can set a filter (See attached).
If the amps come from a fieldbus then I agree that the above mentioned blocks should be used.

grnick50 · Oct 31, 2014

Further to my previous post pls find attached part of the manual discribing the filtering method used in the AI module. I think it is the same method proposed in the previous posts.

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