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Author Topic: MEMM  (Read 82770 times)

MeggerMan

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Re: MEMM
« Reply #105 on: November 18, 2006, 08:13:59 PM »
Hi Paul,
Yes I did just change it, something a bit different I suppose.

The meter consumes 40mA according to the manual but I guess that I would need to couple it to a scope in case they are charging up a capacitor to give it a wallop of say an amp for 1 ms.

Regards

Rob

PaulLowrance

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Re: MEMM
« Reply #106 on: November 19, 2006, 04:23:01 PM »
Hi Rob,


Wow! That's really saturating. :)  I quickly counted 42 turns on your MEG.  Might be off a few.  Is that close?  I did this in FEMM using my core material, which requires about 1.7 times less applied field to saturate than your core. A few weeks ago I created a FEMM model for my material.  At 42 turns my core saturates at just 8 mA.  Although it only requires 2 mA reach half saturation.

These cores are awesome! I'm convinced there's enough stray 60 Hz current to saturate these cores just by touching one of the winding wires. Anyhow, even if an induction meter generated say 0.5 mA the core would still be saturated unless you first degauss the core because these cores have high coercivity-- square BH curves.  So first, the L meter would have to degauss the core and then apply the 0.5 mA AC.

You bring up a good point about a possible cap in meter that might generate an initial current surge. Personally I wouldn't spend any time on measuring the cores inductance and Q for now. If for some reason you cannot replicate Naudin's scope shots then it might pay off to build a simple degasser.  I built one out of a 10 turn high precision pot and a 60 Hz AC voltage source. You only need to make sure the initial current, depending how many turns on your core, is enough to fully saturate the core, and the final current is definitely low enough after turning the pot all the way.  The idea is apply 60 Hz AC current and then slowly decrease the current.  You could do the same with a fancy circuit, but I'm always in a hurry.  Although, given that these cores are ridiculously sensitive it is very difficult to keep these cores degaussed.  As you know, the human body is a big capacitive antenna. Just getting close to the wires generates AC current. And what about radio signals?  There are dozens of radio stations near by. So the wires could pick up these signals.


Regards,
Paul Lowrance

MeggerMan

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Re: MEMM
« Reply #107 on: November 20, 2006, 12:32:49 AM »
Hi Paul,

Bit off topic, but I have just finished fitting a blue LED illumination disc between the fan switch and the ceiling in the bathroom.
Made it from a GU10 LED lamp (18 blue LEDs) and some 10mm acrylic sheet (shaped using a table router). Had to break all the glass away from the PCB boad using a drill vice, desolder each LED and then shaped the PCB to fit into the back of the switch.
Looks very good (bright blue glow) when you switch on the fan now.

I have to agree with you about the low current saturating the core, from all my FEMM sims it was nearly always around the 10 to 20mA of current at 500 turns for this size of core even for silicon steel.

I am fosusing on building the pulse circuit now and I need to work out the capacitors required to create the overlapping freqencies.
I have log and lin 10K pots, so one of them should provide a linear sweep over the frequency, not sure which so I ordered both.

Regards

Rob

PaulLowrance

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Re: MEMM
« Reply #108 on: November 22, 2006, 04:50:25 PM »
Quote from: kingrs
I have to agree with you about the low current saturating the core, from all my FEMM sims it was nearly always around the 10 to 20mA of current at 500 turns for this size of core even for silicon steel.
Supposedly your core has permeability of 600000 as compared to like 5000 to 10000 for SiFe. :-)



Quote from: kingrs
I am fosusing on building the pulse circuit now and I need to work out the capacitors required to create the overlapping freqencies.
I have log and lin 10K pots, so one of them should provide a linear sweep over the frequency, not sure which so I ordered both.
You're still replicating the Naudins MEG?  I think the MEGv2.1 is a good start since that seems to be the only Metglas MEG that Naudin shows all the necessary voltage and current scope shots.


Regards,
Paul Lowrance

MeggerMan

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Re: MEMM
« Reply #109 on: November 23, 2006, 01:40:34 PM »
Hi Paul.

I may try this to build this after the MEG is complete:
http://www.ee.surrey.ac.uk/Workshop/advice/coils/BH_measure.html

Then I can plot the curve for the frequency that JLN came up with.

It would be very interesting to see how the ferrite magnet in place alters the relative permability of the core compared to a vacumm.
In theory the permeability should increase dramatically.

Regards

Rob

MeggerMan

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Re: MEMM
« Reply #110 on: November 27, 2006, 01:02:43 AM »
Hi Paul,

Just working out the frequencies now.
You can roughly calculate them but there is no pattern that I can work out to calculate the exact result.

TL494 push pull breadboard testing pics:
(http://i100.photobucket.com/albums/m25/kingrs/DSCN4768.jpg)
(http://i100.photobucket.com/albums/m25/kingrs/DSCN4769.jpg)
(http://i100.photobucket.com/albums/m25/kingrs/DSCN4770.jpg)

Fan light I was telling you about.
(http://i100.photobucket.com/albums/m25/kingrs/DSCN4766.jpg)
(http://i100.photobucket.com/albums/m25/kingrs/DSCN4767.jpg)

Regards

Rob

MeggerMan

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Re: MEMM
« Reply #111 on: November 28, 2006, 04:08:37 AM »
Hi Paul,
According to a write up for the TL494 the frequency for push-pull setup should be:
http://focus.ti.com/lit/an/slva001d/slva001d.pdf

f = 1/(2 * R * C)

But as usual it does not quite work out correctly.

It is possible that there is some capacitance on the breadboard itself but I cannot see this being more than 100 pf.
Its out by about 35% on the larger capacitance (88nf) and gets better, 27% for 10nf, on the lower the capacitance so that rules out the stray capacitance idea.

I will add a supply capacitor across the chips supply rails just in case its that.
Last thing I need is an unstable push-pull pulse circuit.
Its lower limit looks like to be about 365Hz where the spec. tells you that its 1kHz.
Pity, I was hoping to get down to about 10Hz.

Regards

Rob

gyulasun

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Re: MEMM
« Reply #112 on: November 28, 2006, 11:56:09 AM »
Hi Rob,

I suggest using a 1uF timing capacitor at  Pin 5 of the TL 494 to get to the lower 10Hz frequencies.
From the writings of your link, Page 8, in Fig. 6 you can see the 1uF value for the lower 10Hz operation and this goes with a 200-300 kOhm timing RT resistor, preferably a potentiometer of 220 kOhm. With these two values you can go up to maybe 1kHz from the few tens of Hz, so you have to switch in a lower value timing capacitor to reach higher frequencies. A good solution at the potmeters to connect a 22kOhm one in SERIES with a 220kOhm to get fine tuning possibility and to avoid switching the potmeters when higher frequencies are needed.

If you cannot get near to the lower 10Hzs with the 1uF/220kOhm, then I suggest bending out Pin 5 and Pin 6 pf the TL494 horizontally to disconnect them from the board and solder directly the cap and potmeter wires to these pins.

rgds
Gyula

PaulLowrance

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Re: MEMM
« Reply #113 on: November 28, 2006, 05:49:46 PM »
Hi Rob,

That's odd.  Are you sure your cap isn't 88 pF? What's your timing resistor value?  My datasheet shows the TL494 having the following range -->

minimum 0.47 nF and maximum 10000 nF for timing cap
minimum of 1.8 Kohm and maximum of 500 Kohm for timing resistor.

That should give a range of 0.1 Hz to nearly 600 KHz, but that's probably not the valid frequency range.  I don't see how your circuit could have anywhere near a few nF stray capacitance.

What's your Vcc?  Valid ranges is 7 to 41 V. 

http://focus.ti.com/lit/ds/symlink/tl494.pdf


Regards,
Paul Lowrance

MeggerMan

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Re: MEMM
« Reply #114 on: November 29, 2006, 01:41:25 AM »
It looks like the value of the discharge resistor causes some issues if it is too high for the larger caps. 20k or above with 0.47uf and it jumps all over the place.
At the higher frequencies like 1kHz and above it is not so much an issue.
With testing I can get down to about 10Hz but I have to use a resistor of about 1k + 10k pot.(big frequency swing though).
Also I have managed to get the duty cycle working, 47% down to 0% (off), although the meter flakes out at about 5% and then shows it as 99.8%???
I can see on the scope that it is about 2% but the meter tells me different.

24khz on the scope with storage so I could get a photo, sorry for the poor quality.
Notice the alternating pulses, it does work so far!
(http://i100.photobucket.com/albums/m25/kingrs/IMG_1413.jpg)

734kHz scope trace, maxed out with no caps.
(http://i100.photobucket.com/albums/m25/kingrs/IMG_1414.jpg)

Regards

Rob

MeggerMan

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Re: MEMM
« Reply #115 on: December 16, 2006, 11:42:28 AM »
Pulse output results so far:
12 ranges tested with the capacitor leg lifted off the breadboard and coupled direct to the capacitors. Some of the capacitance values where I combined 2 or more capacitors have been measured with a TENMA 72-960 LCR meter.

Resistance swing is 9.95kR - 52.8kR using a 47kR trimmer and a 10kR resistor.

1. 200kHz - 533kHz 22pF,
2. 80kHz - 300kHz 110pF,
3. 25kHz - 110kHz 468pF,
4. 12kHz - 35kHz 1200pF,
5. 6kHz - 20kHz 2200pF,
6. 3.5kHz - 12kHz 3.9nF,
7. 1.2kHz - 5kHz 10nF,
8. 600Hz - 2kHz 22nF,
9. 300Hz - 1000Hz 47nF,
10. 155Hz - 500Hz 89nF,
11. 100Hz - 290Hz 146nF,
12. 40Hz - 132Hz 386nF

Other ranges I also tested that will not be included in my 12 frequency range pulse unit:
25Hz - 80Hz 600nF
13Hz - 40Hz 1.1uF
5.7Hz - 17Hz 2.5uF

Note that the ranges 11 and 12 and the 3 above all had a some level of double pulsing:
Example, the first output of the TL494 - Q1 would show two pulses widths together and the output for Q2 would at the same period show two spaces, which is fine, except that the frequency is now altered slightly.
It is quite rare, only occurring once every 2-3 seconds or so.
This is not bad going considering the chips minimum frequency is specified as 1Khz and I am pushing this down to 5Hz.
I think I have improved the stability by applying a 0.1uF capacitor across the GND and Vcc.

Next step is to test a MOSFET coupled to it and then design a PCB for it all.

The front panel will have:
12V in (pulse supply)
power LED
0-30V in (MOSFET supply)
A out
B out
f Range select (1-12)
f fine tune
duty adjust
output control switch(push-pull / push)
I will leave a space in the top left of the panel for a 2-line LCD display for future expansion. (frequency and duty info display)

So far so good.

Regards

Rob
« Last Edit: December 19, 2006, 07:15:20 PM by kingrs »

eldarion

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Re: MEMM
« Reply #116 on: December 20, 2006, 10:49:56 PM »
Count me in on the replication project! :)

I ordered my Metglas C-cores today, hopefully they will come in the next couple weeks.

Excellent work Paul!

Eldarion