Maker Pro
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Tonghui TH2821A LCR Meter

J

John S

Jan 1, 1970
0
That's good info. Too low to turn on bipolar junctions.

The 10kHz setting produced 217mV while attached to the primary. Still
low enough.

Unloaded output from the Tonghui:

Hz Vrms
100 288mV
120 287mV
1k 274mV
10k 133mV

Some loading is to be expected. But, still low enough even at no load. Good!

But
what is the last line showing 247 volts and 0.66H?

I think it is due to line wrap with all the >'s building up: Original was...

E(source) V(L) XL(calc) L(calc)
5 3 450 1.2H
3 1.5 350 .92H
.1 .038 247 .66H
[...]
You're welcome. I think this is now outside the Tonghui subject
into the subject of magnetics. The lesson, though, is don't trust
LCR meters with their low excitation to give valid results on
large magnetics.

It looks like you have opened a Pandora's box issue. We need to
learn more why a low-level measurement doesn't work on laminated
cores. What is the mechanism that is causing the discrepancies? Are
there any web links that discuss this in greater detail? Does the
same thing happen on toroids?

All good questions. I have my suspicions, but I'll do some research
before I present them.
This is a very important subject for the Tonghui. If you want to gap
a core, you need to know the inductance you should get after gapping
to confirm it is correct. If the Tonghui can't measure it, I think
we're in trouble.


Well, yes, but not just the Tonghui. This seems to apply to any RLC
instrument that uses low excitation. At least, so it seems for now (Two
in a row). I wouldn't shun further experiments and data.

Thank you,
John S
 
A

amdx

Jan 1, 1970
0
Actually that's pretty good.


Indeed! No complaints from this end.

[...]
No. If I measure the primary inductance on the Tonghui (at 100Hz),
I get about 535mH and Q of 10. That would calculate out to about
600ma of unloaded (magnetizing) current at 124VAC, 60 Hz. If I
then apply 124AC at 60Hz to the primary and measure the current, I
get 0.078mA.
This calculates out to about 4H. I'd like to learn why there is so
much discrepancy.

I've done a couple of investigations since yesterday to try to get to
the bottom of this.

First, I checked my Tonghui data against an old HP4260A Universal
Bridge, bought on eek-Bay and long out of calibration. I can produce the
data if you wish, but the crux of it is that they agree with each other.

Well, I tell myself, the transformer must be producing unexpected data.

First, I checked the Tonghui for output voltage when the transformer was
attached. The lower frequency settings (exclude the 10kHz setting)
produced 98 to 141mV RMS.

I then connected the transformer to an HP audio oscillator set for 60Hz
and an HP3400A RMS meter. The results were not only surprising to me,
but they were good support for the believability of the data produced by
the Tonghui.

E(source) V(L) XL(calc) L(calc)
5 3 450 1.2H
3 1.5 350 .92H
.1 .038 247 .66H

Wow! The inductance goes down as the excitation voltage decreases?

Remember, the Tonghui measured .52H even on the 1kHz setting. That's
plenty good for me.

What this tells me is that I cannot trust *any* RLC meter to give me the
inductance of a 60Hz piece of magnetics at low excitation voltage.

I have a lot more to learn about magnetics. But, the Tonghui is not at
fault and I need more education.

Cheers,
John S

It's all in the "Slope of the BH curve".
At low currents the slope of the BH curve is more vertical and turns
horizontal at higher current.
See the link,

http://www.arnoldmagnetics.com/Non_Grain_Oriented_Electrical_Steel.aspx

Click it, it opens to a pdf, then it is large enough to see the slope of
the initial ramp up, ( the line that starts at 0,0) which is what I
think is similar to the slope at the low currents.
Mikek
 
A

amdx

Jan 1, 1970
0
It's all in the "Slope of the BH curve".
At low currents the slope of the BH curve is more vertical and turns
horizontal at higher current.
See the link,

http://www.arnoldmagnetics.com/Non_Grain_Oriented_Electrical_Steel.aspx

Click it, it opens to a pdf, then it is large enough to see the slope of
the initial ramp up, ( the line that starts at 0,0) which is what I
think is similar to the slope at the low currents.
Mikek

Hey, I got the vertical/ horiz reversed in the last post.

Found a couple of better curves.

Oh, this one is good, at least for my explanation.

http://www.electronics-tutorials.ws/electromagnetism/magnetic-hysteresis.html

The graph, note the air line is horizontal (an aircore would have less
inductance)
See the iron line is more vertical, iron will have more inductance than air.
Now if you have low currents the slope is more like air having lower
inductance.



http://kiran111.hubpages.com/hub/CRGO-core-Laminations-Of-Electrical-Transformer

http://vtuphysics.blogspot.com/2008/07/unit-4.html
Mikek
 
J

josephkk

Jan 1, 1970
0
I have seen it before and seen an explanation that seemed reasonable at
the time. I was a LOT better with magnetics back then (25-30 years ago),
but still no great shakes. I think is may be related to effective air gap
due to the laminations meeting up less than perfectly; not that i remember
any such information.

Maybe someone here who does know something about magnetics can help us out
here.
It looks like you have opened a Pandora's box issue. We need to
learn more why a low-level measurement doesn't work on laminated
cores. What is the mechanism that is causing the discrepancies? Are
there any web links that discuss this in greater detail? Does the
same thing happen on toroids?

Magnetic material is also part of the mess, maybe more important than core
shape. Certainly laminated and tape wound cores may be the most
problematic.
 
J

josephkk

Jan 1, 1970
0
It's all in the "Slope of the BH curve".
At low currents the slope of the BH curve is more vertical and turns
horizontal at higher current.
See the link,

http://www.arnoldmagnetics.com/Non_Grain_Oriented_Electrical_Steel.aspx

Click it, it opens to a pdf, then it is large enough to see the slope of
the initial ramp up, ( the line that starts at 0,0) which is what I
think is similar to the slope at the low currents.
Mikek

In the hysteresis curves please not that there is a small low slope part
just coming off 0,0. That is part of where it is coming from.

?-)
 
T

Tim Williams

Jan 1, 1970
0
josephkk said:
Maybe someone here who does know something about magnetics can help us
out here.

Quite simply, magnetic domains are "sticky". Down at low levels, buried
in the hysteresis loop of the material, small-signal loops are flatter
because few domains are responding.

I'm sure this effect has a strong tempco, since higher temperatures free
more domains (much like dithering a balance to get it to the equilibrium
position despite bearing friction). It's present in all metallic
materials I know of, though you'll have a hard time measuring it in
super-high permeability materials due to the extremely small hysteresis
loop, and in powdered materials, since they have a lot of gap in the
matrix already.

Still, powdered materials yield a fair amount of change:
http://www.micrometals.com/materials_index.html
Mix 26 is the familiar yellow/white toroid used in just about every power
supply, quite cheap and lossy, but high permeability (mu = 75).

I'm trying to remember if I've seen an analogous curve for ferrites. If I
have, I don't remember which manufacturer had the curve...

The tempco is more easily observed in ferrites than metals, since the
curie temperature is lower (which is like a magnetic "melting point"; it
loses all order and ceases to be ferro/ferrimagnetic at that temperature).
Permeability almost always rises on approaching the curie point (which, I
suppose, is like water becoming less viscous as it approaches the boiling
point), which means more domains are being more easily moved; meanwhile,
saturation flux goes down, which means fewer and fewer are staying in
their polarized positions. At curie, Bsat suddenly drops to air-cored
levels.

Well, a gapped core doesn't depend on the core very much, so you're okay
on that one. I'd worry more about the expansion tempco of whatever the
core spacing material is!

Tim
 
A

amdx

Jan 1, 1970
0
In the hysteresis curves please not that there is a small low slope part
just coming off 0,0. That is part of where it is coming from.

?-)
Sorry, can you rephrase that, I don't understand what you wanted to say.
Mikek
 
J

John S

Jan 1, 1970
0
It appears that the proper frequency range is called for to begin
with. Not a big surprise, I guess, considering how hard it must be
to measure 300pF at 100Hz. Not bad, huh?

Actually that's pretty good.


Indeed! No complaints from this end.

[...]

No. If I measure the primary inductance on the Tonghui (at 100Hz),
I get about 535mH and Q of 10. That would calculate out to about
600ma of unloaded (magnetizing) current at 124VAC, 60 Hz. If I
then apply 124AC at 60Hz to the primary and measure the current, I
get 0.078mA.

This calculates out to about 4H. I'd like to learn why there is so
much discrepancy.

I've done a couple of investigations since yesterday to try to get to
the bottom of this.

First, I checked my Tonghui data against an old HP4260A Universal
Bridge, bought on eek-Bay and long out of calibration. I can produce the
data if you wish, but the crux of it is that they agree with each other.

Well, I tell myself, the transformer must be producing unexpected data.

First, I checked the Tonghui for output voltage when the transformer was
attached. The lower frequency settings (exclude the 10kHz setting)
produced 98 to 141mV RMS.

I then connected the transformer to an HP audio oscillator set for 60Hz
and an HP3400A RMS meter. The results were not only surprising to me,
but they were good support for the believability of the data produced by
the Tonghui.

E(source) V(L) XL(calc) L(calc)
5 3 450 1.2H
3 1.5 350 .92H
.1 .038 247 .66H

Wow! The inductance goes down as the excitation voltage decreases?

Remember, the Tonghui measured .52H even on the 1kHz setting. That's
plenty good for me.

What this tells me is that I cannot trust *any* RLC meter to give me the
inductance of a 60Hz piece of magnetics at low excitation voltage.

I have a lot more to learn about magnetics. But, the Tonghui is not at
fault and I need more education.

Cheers,
John S

It's all in the "Slope of the BH curve".
At low currents the slope of the BH curve is more vertical and turns
horizontal at higher current.
See the link,

http://www.arnoldmagnetics.com/Non_Grain_Oriented_Electrical_Steel.aspx

Click it, it opens to a pdf, then it is large enough to see the slope of
the initial ramp up, ( the line that starts at 0,0) which is what I
think is similar to the slope at the low currents.
Mikek

Thanks for the links, Mikek, and for your comments, josephkk.

I spent all morning researching the question. The best answer I could
find was here:

http://www.magmet.com/lamination/pdf/Superperm49.pdf

Note that the AC permeability (page 1) increases with increasing flux
density. A crude estimate of the B involved with my measurements gives
about 60 gauss (.1V @ 100Hz) for the Tonghui and about 600 gauss when
the HP audio oscillator was set for 5V.

The AC permeability would therefore go from about 6000 to about 30,000
for about a 5 to 1 increase in inductance. My actual measurements were
about 2 to 1, but, as I said, this is a very crude estimate.

This doesn't answer *why* the permeability changes, but does point out
that the inductance of cored inductors will change with B. So, I think
we can expect usually lower inductance readings from the Tonghui,
especially for the power magnetics cases.

Here is another shot showing powdered iron core changes of inductance
with flux density:

http://www.micrometals.com/material/AC60HzDsgntxt.html

Cheers,
John S
 
J

josephkk

Jan 1, 1970
0
Sorry, can you rephrase that, I don't understand what you wanted to say.
Mikek

Tim Williams explained it soo much better. At very low flux levels there
is a lower proportion of domains responding (per Ampere Turn) to the
impressed flux, thus lower effective Mu(r) and lower inductance.

?-)
 
A

amdx

Jan 1, 1970
0
Tim Williams explained it soo much better. At very low flux levels there
is a lower proportion of domains responding (per Ampere Turn) to the
impressed flux, thus lower effective Mu(r) and lower inductance.

?-)

That's very good. I have ask a couple of times about this phenomena
and could not generate any interest.
My line of questioning had to do with transformers at the RF input of
a radio. The signal can be as low as 1 uV.(less than a picowatt) I'm
sure when you look at the spec's for *Mu(r) it was measured at much
higher power levels. So the transformers used at these low levels should
have many more turns than the spec's would lead you to believe.
Yet, I have not seen any references to support this.

*Mu(r) I'm assuming this symbol is for initial permeability, I have
not seen it put this way.
Ok, I Googled Mu and got μ.
Ya, I had to copy and paste the symbol.
Thanks, Mikek
 
J

John S

Jan 1, 1970
0
Quite simply, magnetic domains are "sticky". Down at low levels, buried
in the hysteresis loop of the material, small-signal loops are flatter
because few domains are responding.

I'm sure this effect has a strong tempco, since higher temperatures free
more domains (much like dithering a balance to get it to the equilibrium
position despite bearing friction). It's present in all metallic
materials I know of, though you'll have a hard time measuring it in
super-high permeability materials due to the extremely small hysteresis
loop, and in powdered materials, since they have a lot of gap in the
matrix already.

Still, powdered materials yield a fair amount of change:
http://www.micrometals.com/materials_index.html
Mix 26 is the familiar yellow/white toroid used in just about every power
supply, quite cheap and lossy, but high permeability (mu = 75).

I'm trying to remember if I've seen an analogous curve for ferrites. If I
have, I don't remember which manufacturer had the curve...

The tempco is more easily observed in ferrites than metals, since the
curie temperature is lower (which is like a magnetic "melting point"; it
loses all order and ceases to be ferro/ferrimagnetic at that temperature).
Permeability almost always rises on approaching the curie point (which, I
suppose, is like water becoming less viscous as it approaches the boiling
point), which means more domains are being more easily moved; meanwhile,
saturation flux goes down, which means fewer and fewer are staying in
their polarized positions. At curie, Bsat suddenly drops to air-cored
levels.


Well, a gapped core doesn't depend on the core very much, so you're okay
on that one. I'd worry more about the expansion tempco of whatever the
core spacing material is!

Tim

Your explanation makes a lot of sense, Tim. Thanks very much.

John S
 
J

josephkk

Jan 1, 1970
0
That's very good. I have ask a couple of times about this phenomena
and could not generate any interest.
My line of questioning had to do with transformers at the RF input of
a radio. The signal can be as low as 1 uV.(less than a picowatt) I'm
sure when you look at the spec's for *Mu(r) it was measured at much
higher power levels. So the transformers used at these low levels should
have many more turns than the spec's would lead you to believe.
Yet, I have not seen any references to support this.

Not that i claim to really understand this (let alone well), i am pretty
sure that much of this is a material dependant property. Laminated core
power transformers would be rather bad about this (they normally would
have plenty of magnetizing current). And ferrite RF materials would be
very nearly independent of this. But that is just a guess.
*Mu(r) I'm assuming this symbol is for initial permeability, I have
not seen it put this way.

Relative permeability, (Mu of the material/Mu of space).
 
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