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Vcal calculation

Submitted by SinyaWeo on Fri, 27/02/2015 - 11:48

Can someone please explain Vcal calculation?

In source sketch it is defined as 268.97, but on the same line there is another result in comment - (230V x 13) / (9V x 1.2) = 276.9 Calibration.

Which one is the right one then?

And second question is - if I power the unit from 8VAC doorbell transformer, how should I evaluate new calibration value?

Thanks, Milan

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Robert Wall's picture

Re: Vcal calculation

Submitted by Robert Wall on Fri, 27/02/2015 - 13:14.

You can read how the number is derived in Building Blocks > CT and AC power adaptor installation and calibration theory. That should answer both questions.

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SinyaWeo's picture

Re: Vcal calculation

Submitted by SinyaWeo on Fri, 27/02/2015 - 14:09.

I did read the article and it is OK.

One thing remains unexplained - if Vcal formula evaluation is 276.9, why value of 268.97 in the sketch is used?

I know is just 3%, but I do not know why.

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Robert Wall's picture

Re: Vcal calculation

Submitted by Robert Wall on Fri, 27/02/2015 - 16:21.

You'll find a table that I think is correct in Building Blocks > Calibration. The "1.2" in the comment formula is a guess for typical value of the regulation of a small transformer such as is used in plug-top adapters generally (and was indeed close to the actual value for a previous recommended adapter). The accurate figures using the manufacturer's data for our present recommended adapter are in that table.

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