Source Impedance II

V1 = sL1.I1 + sM.I2
V2 = sL2.I2 + sM.I2 - wrong

V2 = sL2.I2 + sM.I1

John S<Sophi.2_at_invalid.org> writes:

On 1/23/2012 12:41 PM, Jessica Shaw wrote:
Hi,

I read this article

http://www.gps.caltech.edu/~jkirschvink/pdfs/coilPaper.pdf


Is he saying on page 409 that four coils if nested can provide
magenetic field in all three axes?

I want to measure the field strength. Can any one recommend a deivce
to do it at the frequency of 100KHz.

jess


Wind, say, 10 turns of some gauge wire onto a pill bottle or something
like that. Connect it to a oscilloscope or whatever you have that can
show amplitude in the millivolts or less. Experiment by moving it
around in your area of interest. If the amplitude is sufficient, try
to calculate what it means. If the amplitude is insufficient, try more
turns of wire.

No guarantee that it will be successful, but it is easy to try.

Absolutely.

I did this when trying to understand the effects of stray magnetic field
around my "shielded" SMPS inductor. I had a 10mm sided square of wire on
the end of a BNC connector, connected to a scope. (Still have it in my
"probes" drawer.

Quite informative, you could wave it around the board at various
distances and angles from the inductor, see how the shielding effect of
copper groundplane varied with frequency for example. Or how far away a
sensitive circuit would need to be. I used my 7A22 plugin for the lower
signal levels. I could have used more turns instead as you suggest, but
I thought the single turn was nicely representative of a "typical" loop
area of a circuit and had just got the the 7A22...

On 1/24/2012 4:58 AM, John Devereux wrote:
John S<Sophi.2_at_invalid.org> writes:

On 1/23/2012 12:41 PM, Jessica Shaw wrote:
Hi,

I read this article

http://www.gps.caltech.edu/~jkirschvink/pdfs/coilPaper.pdf


Is he saying on page 409 that four coils if nested can provide
magenetic field in all three axes?

I want to measure the field strength. Can any one recommend a deivce
to do it at the frequency of 100KHz.

jess


Wind, say, 10 turns of some gauge wire onto a pill bottle or something
like that. Connect it to a oscilloscope or whatever you have that can
show amplitude in the millivolts or less. Experiment by moving it
around in your area of interest. If the amplitude is sufficient, try
to calculate what it means. If the amplitude is insufficient, try more
turns of wire.

No guarantee that it will be successful, but it is easy to try.

Absolutely.

I did this when trying to understand the effects of stray magnetic field
around my "shielded" SMPS inductor. I had a 10mm sided square of wire on
the end of a BNC connector, connected to a scope. (Still have it in my
"probes" drawer.

Quite informative, you could wave it around the board at various
distances and angles from the inductor, see how the shielding effect of
copper groundplane varied with frequency for example. Or how far away a
sensitive circuit would need to be. I used my 7A22 plugin for the lower
signal levels. I could have used more turns instead as you suggest, but
I thought the single turn was nicely representative of a "typical" loop
area of a circuit and had just got the the 7A22...


This consultant uses single-turn coils to investigate stuff. I
frequently re-read his papers to remind myself of some simple
techniques to get things done.

http://emcesd.com/

Browse the site and look for probes, loops, etc. Quite enlightening.

On Thu, 19 Jan 2012 02:33:20 -0800,BillSlomanwrote:
I'd read everything that I could on transformers for years
before I came across the transformer equation

V1 = L1. dI1/dt +  M. dI2/dt

V2 = M. dI1/dt  + L2. dI2/dt

It's in  every electrical engineering textbook I've read. Even radio
ham books.

EE101 stuff.

Hi,

My first confusion is how can I define my sources. My source is Square
wave of 100KHz frequency. The MOSFETS turns ON for 2.5 usec and stay
OFF for rest of the time(7.5 usecs) . RL series resonant circuit
shapes the input square wave  to sine wave of 100KHz. The inductors L1
and L2 gets 400 Volts peak to peak as shown in the figure

 http://img269.imageshack.us/img269/8108/seriesw.jpg

 So, will it be correct to say that the source is

vL1(t) = 400 sin ( wt + 0)  where w = 2x pi x 100,000   (across L1 )
vL2(t) = 400 sin ( wt + 0)  where w = 2x pi x 100,000   (across L2 )

v1 (t) = 400 sin ( 628.3 x 10 ^3 t ) + 400 sin ( 628.3 x 10 ^3 t )
( current entering form the same direction) or same dot convention)

and v2 (t) is the voltage across the secondary coil placed in the
magnetic field generated by coils L1 and L2 together can be defined

as

v2(t) = 40 sin ( 628.3 x 10 ^3 t )  [ 40 V is peak to peak voltage
across the secondary coil ]

Am I right ?

My first confusion is how can I define my sources. My source is Square
wave of 100KHz frequency. The MOSFETS truns ON for 2.5 usec and stay
OFF for rest of the time(7.5 usecs) .

RL series resonant circuit
shapes the input square wave to sine wave of 100KHz. The inductors L1
and L2 gets 400 Volts peak to peak as shown in the figure

You are applying a square wave voltage drive to an inductor in series
with a capacitor; if the square wave was high and low for equal amounts
of time, it would allows the square wave to decomposed into the sum of a
sine wave at the same frequency as the square wave and a series of the
odd harmonics of that sine wave (three times the frequency, five time
the frequency and so forth) of ever-decreasing amplitude (one third of
the amplitude of the fundamental, one fifth and so forth) up to an upper
limit set by the switching times of the MOSFETs (typically some tens of
MHz)

Since your MOSFETs are are on for 2.5usec and off for 7.5usec - which
ones, and in what relationship, you've yet to tell us - this isn't what
is happening. But it does tell me enough to let me answer your question
below in the negative.

The current going through the "resonant" circuit is going to depend on
its impedance - which is going to be different at the fundamental and
each of the harmonics - and you probably ought to measure it to get some
idea of what is actually going on.

Note that if the voltages applied across the bridge don't have a 50%
duty cycle, you will get even harmonics as well.

On Tue, 24 Jan 2012 10:58:11 -0800, Jessica Shaw wrote:

My first confusion is how can I define my sources. My source is Square
wave of 100KHz frequency. The MOSFETS truns ON for 2.5 usec and stay
OFF for rest of the time(7.5 usecs) .

Are you sure? Don't you mean 2.5us on, 2.5us off? The H bridge should
reverse every 5us.

oooh you stepped on yourself; t-period is 10 us. ?-(

RL series resonant circuit
shapes the input square wave to sine wave of 100KHz. The inductors L1
and L2 gets 400 Volts peak to peak as shown in the figure

I think you mean *LC* resonant circuit.

I don't see where you're trying to go with the rest. If you're trying to
derive the coupling coefficient of your "search" coil, forget it, it will
alter with position and alignment within the field.

If what you're trying to do is plot the field, the best you can hope to
achieve is *relative* measurements.

oooh you stepped on yourself; t-period is 10 us. ?-(

If you do the right first year electronics course - "The Art of
Electronics" was written as the text-book for the "electronics for
physicists" course at Harvard, so you can't rely on students being
exposed to it.

On Wed, 25 Jan 2012 00:37:28 -0800, Bill Sloman wrote:
If you do the right first year electronics course - "The Art of
Electronics" was written as the text-book for the "electronics for
physicists" course at Harvard, so you can't rely on students being
exposed to it.

I suspect physicists are expected to know it from physics. It's in
"Electricity and Magnetism" (Bleaney & Bleaney). Remember that? It used to
be Holy Writ on your side of the Pond.

On Thu, 26 Jan 2012 21:18:57 -0800, josephkk wrote:

oooh you stepped on yourself; t-period is 10 us. ?-(

Guess I sorta did. The way I defined the sources in my model was:
period=10us, Ton= 5us-Td, Tdelay=5us on opposing diagonals. Td (dead time)
made steppable. I tend to think in terms of dead time when describing
bridge excitation.

PULSE(0.85 11.05 0 25n 25n {5u-Td} 10u)

PULSE(0.85 11.05 5u 25n 25n {5u-Td} 10u)

To me, that's 5us minus dead time on, 5us plus dead time off, reversing on
alternate half cycles.

I used to worry about it, until I started having to supervise
university trained electronic engineers

On Fri, 27 Jan 2012 15:16:42 -0800, Bill Sloman wrote:
I used to worry about it, until I started having to supervise
university trained electronic engineers

Robots?

I think you mean *electronics* engineers