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Re: Measuring Coupling Coefficients


From: 	John H. Couture[SMTP:couturejh-at-worldnet.att-dot-net]
Sent: 	Wednesday, November 26, 1997 10:45 PM
To: 	Tesla List
Subject: 	Re: Measuring Coupling Coefficients

At 04:17 AM 11/26/97 +0000, you wrote:
>
>From: 	terryf-at-verinet-dot-com[SMTP:terryf-at-verinet-dot-com]
>Sent: 	Tuesday, November 25, 1997 4:23 PM
>To: 	Tesla List
>Subject: 	Measuring Coupling Coefficients
>
>Hi All,
>        I have been playing with measuring coupling coefficients lately.  I
>was just wondering if anyone has a relatively easy way to accurately measure
>this elusive factor?
>        I have tried measuring the coils in series so that the inductances
>add and then subtract and then applying the formula M=(La-Lb)/4.  However,
>due to the large difference in the primary and secondary inductances (two
>orders of magnitude) this formula can introduce substantial error.
>        I have been able to load the output with a 10K ohm resistor and use
>a 50 ohm voltage source to determine K.  However, the frequency needs to be
>carefully selected to insure an accurate reading, the math involved in the
>calculation is very complex (the compter does all the work:-)), and it takes
>substantial test equipment to perform.  So far this is the best method I
>have found and it seems to work very well but I just want to be sure I
>haven't missed some simpler method.
>
>Any thoughts / comments welcome.
>
>        Terry
>        terryf-at-verinet-dot-com

---------------------------------------------------------------------

  Terry -

  I agree the method you are using to find the coupling coefficient is not
very good. There are two tests that are much better and easier to implement.
One is shown in my Tesla Coil Construction Guide. The other is shown in a
sheet that is in the Tesla Coil Notebook.

  If you want to find the coupling coefficient before the coil is built and
tested the JHCTES TC computer program will determine it for you. It is the
only TC computer program that can find this parameter at the design stage.
It is accurate to +/- 10% and has been used successfully by many coilers.
You can find the hundreds of Tesla coils possible with .05 to .70 coupling
coefficients.

With this program you can find the coupling coefficient of dozens of
combinations of Tesla coil parameters without having to build the coils and
test them. For example you can find the critical coupling (Rp = Rs) of a
Tesla coil before it is built and be the first person in the world to find
this parameter for a particular coil assuming it has never been built and
tested. This isn't boasting, it is just  coordinating and calculating the
many parameters involved using a computer.

  I am sending you a flyer with more information on the books and the
computer program.

  John Couture