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Re: Inexpensive LCR-Multimeter



Original poster: "Terry Fritz" <teslalist-at-qwest-dot-net>

Hi,

I just wanted to say that my 27XT does seem to easily measure my primary 
coils to about 5% or 10% when the inductance gets really low.  Far better 
than my LCR meter.  The 27XT seem to use a better chipset or 
something.  Excellent meters.  Everyone sells them for about $120 but there 
are good sales and deals on them.

Cheers,

         Terry


At 05:09 PM 1/9/2003 -0700, Dr.Resonance wrote:

>Jim
>
>Any idea of who has the best price on the 27XT?
>
>Dr. Resonance
>
>
>
>----- Original Message -----
>From: "Tesla list" <tesla-at-pupman-dot-com>
>To: <tesla-at-pupman-dot-com>
>Sent: Thursday, January 09, 2003 11:33 AM
>Subject: RE: Inexpensive LCR-Multimeter
>
>
> > Original poster: "Jim Lux by way of Terry Fritz <teslalist-at-qwest-dot-net>"
><jimlux-at-earthlink-dot-net>
> >
> > With respect to the measurement frequency issue that there is a bit of a
> > concern...
> >
> > If the "box" measures the component at 60 Hz or 1 kHz, there is a good
> > chance that parasitic C or L won't be much of a factor.  For the typical
> > telsa coil running at a few hundred kHz, the parasitic C (particularly of
> > the secondary, where the C is part of the resonant circuit), an "apparent
> > inductance" measurement at 100-200 kHz might be very very different from
> > that measured at 60 or 1000 Hz.  Of course, one could argue that the 60 Hz
> > measurement of the L is actually more accurate, because the error in
> > measurement due to C is much, much less.
> >
> > It kind of depends on what you are trying to measure, I suppose....
> >
> > I would think that as long as the device you are measuring is within the
> > measurement range of the instrument, you're probably ok with the cheap
> > device.  I wouldn't try measuring 0.05 picofarad caps with a $60
> > instrument, both because the reactance is so high at the likely
>measurement
> > frequency that it is hard to make the measurement, and because the "test
> > fixture" is going to contribute a lot of error.  Likewise, measuring the
> > inductance of a 12" piece of wire (about 0.3 uH) is going to be iffy.
>But,
> > in both cases, it's because the instrument isn't suited to the test
> > article, not because the $60 widget isn't a decent meter.
> >
> > I suspect that environmental effects and test fixtures will dominate any
> > but the most careful of component measurements in tesla coiling, and a
> > meter that claims, for instance, 5% accuracy, would be more than good
> > enough. The 27XT claims basic accuracy of 0.5%, capacitance range from
> > 0.1nF to 2000 uF, and inductance from 0.1mH to 20H.  Since the latter has
>5
> > ranges, I'm going to guess that the ranges top out at 20H,2H,200 mH, 20mH,
> > and 2mH.  The 0.1 mH is 5% of full scale on the 2mH and since it is a 1999
> > count device, that reading is 100 counts, so the 0.5% accuracy is
> > consistent (the meter only has a display precision of 1% for that 0.1mH
> > inductor).
> >
> > http://www.metermantesttools-dot-com/downloads/DataSheets/DMM/XTSeries.pdf
> >
> > Looking at the spec sheet (above) in more detail, I see that the
> > capacitance accuracy is 5% +10 (counts?) on the 27XT (interestingly, the
> > 25XT is actually a bit better..)
> > For inducatance, the accuracy is +/-5% + 30/1uH and they use 1000 Hz as a
> > test freq on the two low ranges (2 and 20 mH).. At 1000 Hz, the reactance
> > of 2 mH is about 12.5 ohms, so things like lead resistance shouldn't throw
> > the reading off that much.
> > (I wonder how the meter measures inductance?  If it measures voltage and
> > current, does it also measure the DC resistance, and take that into
>account?)
> >
> >
> > At 04:57 PM 1/8/2003 -0700, you wrote:
> > >Original poster: "Lau, Gary by way of Terry Fritz <teslalist-at-qwest-dot-net>"
> > ><Gary.Lau-at-hp-dot-com>
> > >
> > >Which things are useless, LCR multimeters?  I can't speak for the $60
>unit
> > >offered by Ocean State Electronics, but the experience of myself and
>other
> > >on this List with the Wavetek 27XT has been that it's very accurate for
> > >both primary and secondary inductance measurements, as well as
> > >capacitance, and frequency.
> > >
> > >Why is it necessary to measure inductance at different frequencies?  My
> > >characterizations of different primary coils with a _very_ expensive
> > >HP4194 impedance/gain-phase analyzer showed negligible variation of
> > >inductance with frequency.
> > >
> > >40 years ago, who would have believed that restaurants would give away
> > >digital wristwatches with a hamburger?  Technology advances and what used
> > >to be costly becomes cheap.
> > >
> > >Gary Lau
> > >MA, USA
> > >
> > >
> > >Original poster: "Mccauley, Daniel H by way of Terry Fritz
> > ><teslalist-at-qwest-dot-net>" <daniel.h.mccauley-at-lmco-dot-com>
> > >
> > >In my experience, these things are basically useless for inductance
> > >measurements.
> > >
> > >You should really try to get a dedicated LCR meter which can measure
> > >inductances at a variety of
> > >different frequencies.  There is a place that sells very high quality LCR
> > >meter kits for about $50.00
> > >High quality in that the readings are extremely accurate.
> > >
> > >I'll try to dig up that source.
> > >
> > >Remember the old addage.  You get what you pay for.  Multimeters that
>have
> > >every single function known to man
> > >especially for those prices are usually garbage.
> > >
> > >Dan
> >
> >
> >
> >