Re: Inexpensive LCR-Multimeter

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Dr.Resonance by way of Terry Fritz <teslalist-at-qwest-dot-net>" <resonance-at-jvlnet-dot-com>


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
 >
 >
 >
 >