Re: 20 Khz output/true rms?

["Paul Benham" <Paulb-at-xxxxxxxxxxxxxxxxxxxx> (by way of Terry Fritz <twftesla-at-xxxxxxxxxx>)]

When using any meter to measure current you need to be careful about the
meters internal series resistance.  On a lot of meters the internal
resistance varies as you change range, and sometimes as you change to a
smaller range the current reading drops.  It is due to the voltage drop
across the meter going up, so the resulting circuit current dropping.

A meters internal resistance can always be measured by using another,
and the difference between ranges can be quite a lot.  I always try and
use the meter set to the largest range I can.

I hope this is of help,

Paul.

Tesla list wrote:
> 
> Original poster: "harvey norris" <harvich-at-yahoo-dot-com>
> 
> --- Tesla list <tesla-at-pupman-dot-com> wrote:
> > Original poster: MrDirect-at-aol-dot-com
> >
> > Hello
> >
> > I have a radio shack true rms meter that had a DC
> > voltage measurement.  It
> > has a frequency counter up to 2 Mhz.
> > I have used this same meter to record the frequency
> of an AC alternator at 188 hz . I have also scoped
> this, it appears to be accurate for these lower
> ranges.
> However I have taken the meter back Radio Shack for a
> replacement that has not yet arrived. It will not
> record low amperages at all. The 56 Henry coil shows
> .07 amps on full scale reading, .07 ma onthe next
> scale down and the .04 uA on the smallest scale! The
> ordinanry meter reads 5.60 ma with no problem. I went
> to Radio Shack, brought the  80 lb coil to show them
> what was happening, they have no answers except, well
> we dont have a replacement in stock. I have a feeling
> the replacement meter will do the same thing. I have
> had some correspondence with a radio shack engineer,
> which I will resume if the new meter does the same
> thing. I would be cautious with purchasing these new
> auto ranging meters, especially if you are attempting
> small amperage mesurements. To see the possible
> variations in amperage consumption I also series
> resonated the coil at 440 volts, the amperage
> consumption at these higher levels is still markedly
> different on the auto ranging, true rms meter.
> > I am trying to measure the voltage off a DC
> > transformer and it is measuring
> > 10 volts.  It cannot provide an accurate reading
> > because of the differences
> > in frequencies.
> >
> > The transformer is supposedly -at- 20 Khz.
> >
> > Does anyone know a formula I might use to determine
> > what the 10 volt
> > measurement on the volt meter really is?
> >
> > Thanks
> 
> Got me, I never heard of a 20 thousand hz DC
> transformer?   HDN
> 
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