[R-390] DMM bounce

[Dan Merz]

Hi Joe and others,   I confirmed that the problem was due to autoranging
bounce combined with the high inductance of the secondary of the
transformer.  There's too much inductance for the meter to settle down
and make a reading of resistance.  I confirmed this with a small pocket
RS multimeter that has only autoranging.  On the secondary winding,  it
just keeps flipping from 0 to OL reading when trying to read the
secondary resistance.  On the primary,  which is lower inductance,  it
flips once or twice then stabilizes on the correct 400 ohm resistance
reading.   As I mentioned,  I had no problem reading this with my BK
average quality,  non-autoranging meter and I checked it with the $4
meter I bought from Harbor Freight,  which of course is not
autoranging.  The guy I sent the transformer to was using a Fluke meter
on autoranging,  which was the start of this escapade.    The moral:
never send in a man to do a boys job,  and of course if you have a
Harbor Freight model,  you can send in a baby.   And the Fluke can be
trained for the job by turning off the autoranging.     Thanks for the
comments.  I far as I know there are no inductances in a 390a that are
large enough to cause this problem .  But I have only a smattering of
knowledge about the various ways that today's exotic meters perform all
their magic.  Dan.

Joe Foley wrote:

> --- Dan Merz <djmerz at 3-cities.com> wrote:
> > Hi Joe,  my DMM is BK 2905 calibrated with dc and
> > for ac with 400 hz.  I
> > have no idea yet of  details on the other guy's
> > meters except I think
> > they are autoranging type for ordinary dc and 60 hz
> > measurements.  I'll
> > try to get more details on his meter but I don't
> > think they are types
> > for measuring much above 5 khz.  I use my meter
> > occasionally for
> > measuring up to 5 khz,  though I have no idea how
> > accurate it really is
> > up there but I use it to get voltage ratios for
> > evaluating audio
> > transformers.   I have checked it  against my HP
> > 403B meter and decided
> > for what I was doing it was good enough.   It reads
> > about 3% low at 12
> > khz and close on up to 7 khz.    Thanks for any
> > thoughts on my
> > question,  best regards,  Dan.
> ++++++++
> I just took a stab at it, you're more experienced at
> this than I am, I'm surprised its that close at audio
> levels.  But I guess that wasn't the problem anyway.
>
> Still, though, it IS the frequency that determines the
> impedence, so I might not be far off.
>
> 73
>
> Joe
>
>
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