MEMM

[MeggerMan]

Hi Paul,
Sorry, don't get too excited yet, it looks like the meter takes time to give an accurate reading.
I tried it again and it is not conclusive, in fact placing a ceramic magnet into the core has little effect on the inductance and Q value.
I placed the core onto a 1' cube polystyrene block in the middle of the kitchen floor away from metal objects and found that even after waiting for the meter to settle the reading barely changed when the core was rotated though the 360 deg.


They are as follows:

Inductance = 11.04mH
Q value = 42.0

Coil = 42 turns of 0.56mm enamelled copper wire wound on the middle on one of the "C" halves.

Things may look different when the core is operating at 25kHz.

Regards

Rob

[PaulLowrance]

Rob,

That's why I was surprised that simply changing the orientation changed the inductance that much. A few percent sounded like a lot from just simply rotating, but whatever. :-) Rotating just changes the transverse alignment, but the Earths and stray fields are still there. Now you say it _barely_ changes ... that's fine. I have been focusing on nulling out Earths magnetic field and stray radio fields. They do indeed make a difference when performing the MCE experiment. :-(

Regards,
Paul Lowrance

[PaulLowrance]

I tried it again and it is not conclusive, in fact placing a ceramic magnet into the core has little effect on the inductance and Q value.

Rob,

If that's your final conclusion then there must be something wrong with your meter. I don't think there's a core on Earth that remains unchanged by placing a magnet on it.

I'm curious what the problem is.

Regard,
Paul

[PaulLowrance]

Rob,

I had a thought why you are getting varying results.  As previously stated many times, these Metglas cores have square BH curves. Also the cores require very little stray fields to saturate. I've seen even slight 60 Hz stray fields cause the core to saturate. Once the core is saturated then it doesn't matter if you remove all the stray fields-- the core remains saturated unless you degauss it. The Metglas BH graphs show the proof how sensitive these cores are to transverse fields. BTW, my metglas core is more sensitive to transverse fields than yours ... lucky me.

If your core is already saturated then that could easily explain why even a PM has less affect on inductance. I have been fighting with these Metglas cores for several weeks now. They are so pernickety it's a nightmare as far as MCE experiments go. As far as inductance measurements ... I'll leave that task up to you. ;-)


Regards,
Paul Lowrance

[MeggerMan]

Hi Paul,
The Ceramic magnets have now arrived, and they are a perfect sliding fit, a single turn of pvc tape around the center magnet and they form a tight fit.
I did a re-test on the meter and it looks as if it may be the pvc tape binding the core is relaxing, so this may explain the gradual changes.
Certainly placing a magnet in the core is now changing the Q and inductance.

Q Value	Inductance mH	Mag Centre	Mag on Leg
39.1	11.75	N	N
38.5	10.73	Y	N
36.0	11.25	N	Y

"Mag on leg" means the magnet stack is attached to the left leg pointing in towards the core centre.



Regards

Rob