Tonghui TH2821A LCR Meter

On 1/16/2012 4:16 PM, Mike wrote:
John S<Sophi.2_at_invalid.org> wrote:

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

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

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?

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.

Cheers,
John S

Thanks,

Mike

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

low level inductance

Maybe someone here who does know something about magnetics can help us
out here.

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.

On Tue, 17 Jan 2012 17:50:47 -0600, amdx<amdx_at_knologynotthis.net> wrote:


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


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.

On 1/17/2012 3:27 PM, John S wrote:
On 1/16/2012 4:16 PM, Mike wrote:
John S<Sophi.2_at_invalid.org> wrote:

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

On 1/17/2012 9:38 PM, josephkk wrote:
On Tue, 17 Jan 2012 17:50:47 -0600, amdx<amdx_at_knologynotthis.net> wrote:


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


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

On Wed, 18 Jan 2012 06:40:57 -0600, amdx <amdx_at_knologynotthis.net> wrote:

On 1/17/2012 9:38 PM, josephkk wrote:
On Tue, 17 Jan 2012 17:50:47 -0600, amdx<amdx_at_knologynotthis.net> wrote:


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


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

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.

?-)

On Wed, 18 Jan 2012 06:40:57 -0600, amdx<amdx_at_knologynotthis.net> wrote:

On 1/17/2012 9:38 PM, josephkk wrote:
On Tue, 17 Jan 2012 17:50:47 -0600, amdx<amdx_at_knologynotthis.net> wrote:


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


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

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.

?-)

"josephkk"<joseph_barrett_at_sbcglobal.net> wrote in message
news:ruech7leag4uj6kv30qqs99r3a4tk7tub2_at_4ax.com...
low level inductance

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.

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, 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

josephkk wrote:

On Wed, 18 Jan 2012 06:40:57 -0600, amdx <amdx_at_knologynotthis.net> wrote:

On 1/17/2012 9:38 PM, josephkk wrote:
On Tue, 17 Jan 2012 17:50:47 -0600, amdx<amdx_at_knologynotthis.net> wrote:


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


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

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.

?-)

Sort of like a magnetic version of crossover distortion.

Cheers

Phil Hobbs

On 1/18/2012 10:07 PM, josephkk wrote:
On Wed, 18 Jan 2012 06:40:57 -0600, amdx<amdx_at_knologynotthis.net> wrote:

On 1/17/2012 9:38 PM, josephkk wrote:
On Tue, 17 Jan 2012 17:50:47 -0600, amdx<amdx_at_knologynotthis.net> wrote:


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


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

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 ?.
Ya, I had to copy and paste the symbol.
Thanks, Mikek