[time-nuts] Re: My AC measurement project & question

[Jeremy Nichols]

A transformer may distort the waveform but that distortion should be
constant, whereas a person monitoring line voltage at a particular location
will be looking for changes with time. Effects of the transformer could be
ignored, in that case.



On Sun, Jan 23, 2022 at 8:33 AM Bob kb8tq <kb8tq at n1k.org> wrote:

> Hi
>
> On a similar note:
>
> If the transformer works well up to 600Hz, isn’t that high enough to
> capture
> anything that actually is grid related (as opposed to local to your home /
> neighborhood )?
>
> One could easily argue that the other end is the pinch point. There may
> well
> be interesting things going on well below the main frequency. Of course
> you
> then get back to all those other transformers upstream of you …
>
> Bob
>
> > On Jan 23, 2022, at 5:55 AM, Andy Talbot <andy.g4jnt at gmail.com> wrote:
> >
> > But do you want to measure anything other than mains frequency?   IF not,
> > waveform distortion in immaterial.
> > Or am I missing something here?
> >
> > My mains monitor uses an old wall wart with 9V rectified but unregulated
> DC
> > out - 5V regulator on the display board.  I added an extra wire to one
> side
> > of the transformer winding which goes via a DC block capacitor and
> resistor
> > of a few kΩ to the Schmitt timer input of the PIC microcontroller.   At
> > several volts peak to peak, it's more than sufficient to take the Schmitt
> > well beyond its two switching thresholds.  Clamp diodes to Vdd and GND
> > within the PIC keep it to safe limits.
> >
> >
> > Andy
> > www.g4jnt.com
> >
> >
> >
> > On Sun, 23 Jan 2022 at 10:44, Dave B via time-nuts <
> time-nuts at lists.febo.com>
> > wrote:
> >
> >> On 23/01/2022 08:30, time-nuts-request at lists.febo.com wrote:
> >>> Stick with the transformer. The use of a capacitive divider is
> >> predicated on the line waveform always being a sine wave. Dream on! All
> it
> >> takes is one good spike down the line, maybe only 20-30V amplitude, and
> >> your capacitive divider passes it right on to that ADC that has a much
> >> lower (3.3V?) limit. Guess what goes poof?
> >>>
> ------------------------------------------------------------------------
> >>
> >> Transformers distort the waveform, unless specifically designed for that
> >> need.
> >>
> >>
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-- 
Jeremy Nichols
Sent from my iPad 6.