is voltage constant like calibration

Submitted by giuseppean on Sat, 04/07/2015 - 14:33

Hi all,

is calibration == voltage constant ?
can you explain What are the values taken from

voltage constant = 230 × 11 ÷ (9 × 1.20) = 234.26

I guess:
230 = AC input transformer
11 = partition ratio?
9 = out voltage adapter
1.20 = ??

Thank you very much

Re: is voltage constant like calibration

Submitted by calypso_rae on Sat, 04/07/2015 - 17:21.

My guess is that the RMS output from the unloaded transformer will be approx 20% higher that its nominal value of 9V. This signal is then divided by a 10:1 pair of resistors so only 1 eleventh reaches the ADC. So the RMS signal at the ADC's input will be (9V * 1.2) / 11 = 0.9818 Vrms.

The actual voltage on the mains is nominally 230 Vrms, so the cal factor needs to be 230 / 0.9818 = 234.26.

Re: is voltage constant like calibration

Submitted by Robert Wall on Sat, 04/07/2015 - 20:17.

That page was written before the change to Ideal as the supplier of ac adapters. If you look at the Ideal data sheet, the actual output voltage under no-load conditions is specified, so there is no need to guess a value for transformer regulation.

But there are in fact three constants that affect calibration. All the details are in Building Blocks.

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