Measurements using field probe

From:  John H. Couture [SMTP:couturejh-at-worldnet.att-dot-net]
Sent:  Tuesday, June 30, 1998 2:21 AM
To:  Tesla List
Subject:  Re: Measurements using field probe

  Terry, Bert -

  Please excuse the error in giving credit for the light bulb tests to the
wrong person. Regardless of who did the tests I believe we are making
progress in accumulating the information needed to develop an improved
program for designing Tesla coils. Keep up the good work. I will be
interested in seeing more data on the efficiency of your coils.

  John Couture


At 10:50 PM 6/29/98 -0500, you wrote:
>From:  terryf-at-verinet-dot-com [SMTP:terryf-at-verinet-dot-com]
>Sent:  Monday, June 29, 1998 12:46 PM
>To:  Tesla List
>Subject:  Re: Measurements using field probe
>Hi John,
>        The experiments were done by Bert, not me.  Many of the original
>numbers were pulled out of the air to show the I^2R problem.  Bert has since
>posted a much better analysis of his coil measurements that are probably
>very close the truth.  The new numbers are much closer to what we would expect.
>        Bert's note that his halogen light bulb varies in resistance by a
>factor of ten raises some concerns about the accuracy of this type of test.
>A good calorimetric meter would be better but I am not sure it would
>survive.  They are very expensive!!  The fact that Bert is getting such good
>values is due his very good understanding of what his measurement setup is
>doing.  It should be noted that we need to consider that these measurements
>need to be done at perhaps 50MHz signal levels so there are many high
>frequency things that also need to be considered.  Obviously, my antenna
>system vastly simplifies all this but experiments like Bert's provide the
>very important "second opinion".
>        Many my not realize just how far we have come in efficiency
>measurements in the last month.  We can now measure energies and losses in
>output arcs in real time to fair accuracy!  Some of the crosschecks on
>accuracy suggest only a few percent error!  Unfortunately, the output is not
>a simple resistor but is deeply involved in dynamic electrostatic field
>behavior.  Still very manageable, but not easy.  When Q and resonant rise
>were removed from the list of factors, many of the theoretical
>considerations were vastly simplified.  We now pretty much know were all the
>power is going except in two areas.  The spark gap and the secondary arcs.
>Many tests are showing that the energy lost in a well-constructed spark gap
>is fairly low.  Probably not a major concern.  The quenching and good RF
>design are very important but once that is done the gap does a good job at
>not loosing much power.  Hopefully, I will be able to get the fiber probe to
>give better current measurements now that I understand the saturation
>problem.  In many ways the output arcs are very similar to the gap arcs.  It
>appears that good RF design is also important here as well.  I suspect that
>a large, smooth, highly conductive top terminal will perform much better
>than the opposite.  I have not sat down and gone through all the
>efficiencies for my coil, but I suspect well made coils are very efficient
>in that they are not wasting heat.  Much more can be done to translate the
>energy into sparks, however.  
>        Terry Fritz
>At 11:23 PM 6/28/98 -0500, you wrote:
>>From:  John H. Couture [SMTP:couturejh-at-worldnet.att-dot-net]
>>Sent:  Sunday, June 28, 1998 7:42 PM
>>To:  Tesla List
>>Subject:  Re: Measurements using field probe
>>  Terry, All -
>>  Congratulations on your "light bulb tests" experiments. Your tests are
>>very important to me and all the other coilers. The lamp meter is an
>>excellent method of measuring currents in an operating TC.  The TC RF
>>currents in the secondary are random pulses at high frequency. Ordinary
>>meters cannot accurately measure these currents. Even hot wire and
>>colometric meters have limited use because they are calibrated for only
>>special conditions.
>>  Using a variety of lamps and suitable shunts and properly calibrated you
>>can measure TC currents for any condition. I made many of these tests
>>several years ago on some of my small coils as I show in my Tesla Coil
>>Construction Guide. Note that the lamp gives an RMS output instead of an
>>average output. Average is 63.7% of peak while RMS is 70.7% of peak. The
>>lamp output is non linear and limited but that can be taken care of by using
>>several different lamps  with appropiate shunts.
>>  I not only measured the TC secondary currents but also was able to find
>>the overall efficiency of some of my coils. This is also shown in the Guide.
>>The efficiency was found to agree closely with the TC efficiency graph (Fig
>>7) I shown in the TC Notebook. As I have not found any coilers who have
>>duplicated the overall efficiency tests I have not been able to verify my
>>results. Hopefully more coilers like you will help me make verification
>>  It is interesting to compare your estimate of 950 KV (at 100% eff) in the
>>secondary with the 462 KV in the JHCTES program. This gives a secondary
>>voltage efficiency of
>>  (462/950) x 100 = 48.6 percent for sec cir, not overall.  
>>  The program shows 8.6 Inst peak amps in the secondary circuit. This gives
>>  462 x 8.6/1000 = 3.97 Inst megawatts in the secondary.
>>  I have not been able to verify your 31.62 amps. Could this current be 
>>  8.6/.486 = 17.69 amps??   and
>>  sqrt(313) = 17.69?
>>  For your toroid and coulomb calcs giving 47.43 uCoul.
>>  The JHCTES program gives for   Q = C x V
>>  (50^-12) x (462000) = 23.1 uCoul   and
>>  (23.1 / 47.43) x 100 = 48.7 percent as above
>>  The sec voltages, uCoul, and eff seem to work but not the sec currents. 
>>  Some experiments appear to agree with calcs but we have a long way to go.
>>We need more coilers to build, test, and do the calcs with more coils to
>>verify the above results. This can be done with small coils and does not
>>require big sparks!!  
>>  John Couture