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Re: 37XR inductance range
Original poster: Terry Fritz <vardin@xxxxxxxxxxxxxxxxxxxxxxx>
Hi Steve,
Ferrites have hysterysis curves too. Any core that can get hot
does. However, "in general", it is low enough not to mess up low
power measurements if there are lots of turns and the core is not too
big. But you really need to find the material specs and check it all
out if you really need to trust a meter measurement.
www.ferroxcube.com and others have such info if you dig hard enough:
http://www.ferroxcube.com/prod/assets/sfintro.pdf
Our ferrite inductor suppliers checked their work with simple meters,
but in some cases we did have to 'fudge" the reading they checked to
because of their low power meters and the core's hysterysis, size,
turns gave skewed readings...
So, it probably is a worry...
A nice low-Z amp (or a stereo audio amp) and a signal generator with
the usual toys can beat any L meter all to heck, it is just more
complex to setup... But then you can often go right to your currents
and frequencies of interest and scan around on the edges for any
possible problems. You just have to be able to measure current,
voltage, and frequency. The signal general and power amplifier are
not terribly critical and can be picked up off e-bay for a song if
you don't already have them. A GenRad 1630AV high power inductance
meter used to run $38,000.00 but they are cheaper used at like $3000:
http://www.used-line.com/c5008261s1723-G_R_1630AV.htm
http://teknetelectronics.com/Search.asp?p_Var1=GENERAL%20RADIO%20-%20QUADTECH%201630AV&pDo=DETAIL
But 1250V to 20 amps over 20 to 20,000Hz... I think the little audio
players kids carry around in their pockets do that nowadays
:o))) Apparently, some kid's cars are now "propelled" by 200 HP
"audio systems"... %:D But if you can find an audio amplifier that
puts out the current you need, your pretty much set!! I think they
still sell audio generator "CDs" for testing too if you don't have a
signal generator but want very accurate signal sources... A computer
sound card could do that too with the software we discussed a while
back... If you series a cap in there too with maybe a little
resistance, you can resonant the voltages way up too if you wish...
Fact is, almost all such measurements are done with odd things laying
about the lab rather than a fancy single machine to do it. The next
step up in needed equipment is a technician that will do it all for
you :-))) Once you get used to using a core material like 3C8, then
you will sort of "know" anyway. Often the inductors are "gapped" too
which adds another twist to it all...
Cheers,
Terry
At 01:43 PM 1/6/2006, you wrote:
Does anyone know if LCR meters are also incompetent for measuring
ferrite based inductors? This could be very bad since the large power
supply ive been developing strongly depends on my LCR meter
measurements.
Anyone know of a good high power home-brew L-meter?
Steve Ward
On 1/6/06, Tesla list <tesla@xxxxxxxxxx> wrote:
> Original poster: Terry Fritz <vardin@xxxxxxxxxxxxxxxxxxxxxxx>
>
> Hi Mike,
>
> What are you measuring? In general, any LCR type meter us useless on
> iron cored inductors or inductors that have a core with a significant
> hysteresis. Since you inductance is relatively high, I assume your
> inductor is cored.
>
> The core needs a certain minimal amount of energizing current to
> reach its normal magnetization curves. Typical meters use very small
> currents that can't energize the iron and such properly. The meter
> uses different current levels for different ranges so the readings
> vary, but the readings are probably far off anyway.
>
> Probably best to run 60Hz AC voltage across it with a variac and
> measure the current. Then you get L = V / (I x 2 x pi x 60).
>
> If you graph the inductance vs current, it starts out very low,
> reaches a long flat area and then drops again as the core saturates.
>
> Cheers,
>
> Terry
>
>
> At 11:51 PM 1/5/2006, you wrote:
> >I recently purchased the Meterman 37XR per the list members
> >favorable use. I was just measuring the inductance of my variable
> >ballast, and a few hig power isolation xfmr I have laying around.
> >One measured 365 mh. When I changed ranges to henrys, it
> >dramatically changed to 0.260H ! Does anyone else notice this vast
> >discrepincy? Can I trust the meter?
>
>
>