[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

*To*: tesla-at-pupman-dot-com*Subject*: Re: New formula for secondary resonant frequency*From*: "Tesla list" <tesla-at-pupman-dot-com>*Date*: Sat, 03 Feb 2001 20:54:15 -0700*Resent-Date*: Sat, 3 Feb 2001 21:13:13 -0700*Resent-From*: tesla-at-pupman-dot-com*Resent-Message-ID*: <MmiKdC.A.avC.WbNf6-at-poodle>*Resent-Sender*: tesla-request-at-pupman-dot-com

Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>" <paul-at-abelian.demon.co.uk> Kurt, Your measured coil results and evaluation of this proposed formula are very much appreciated. Kurt's table: Coil PN-CW PN-half TF-big MM turns 725 365 1001 1700 h 1.6 0.8 0.762 1.07696 m d 0.58 0.58 0.2606 0.1081 m b 0.15 0.15 0.025 0.3302 m awg 12 12 24 24 Fres,cal 91.1 152.9 147.6 279.6 kHz Fres,exp 90.9 150.7 148.4 276.9 kHz Diff 0.2% 1.4% -0.5% 1.0% cal-exp Kurt Schraner <k.schraner-at-datacomm.ch> wrote: > As obvious, there is a difference in the results, relative to > yours, Your figures are correct - mine wrong. Many thanks for pointing out my error - I pasted in the frequencies and percentage errors from an earlier iteration. I prefer your figures :) > As a next, 4 of my own coils are compared: [Kurt - I shrunk the table a little to avoid 72 char wrap] > Coil Sk-B&W Sk-Long Sk-12cm Sk-20cm > turns 821 1950 921 979 > h 1.768 1.41 0.585 0.68 > d 0.4013 0.1633 0.1207 0.2 > b 0.7 0.5 0.2 0.5 > awg 17.162 22.053 22 22 > > Fres,cal 131.4 157.3 409.0 209.3 Paul's formula > Fres,exp 119 147.7 368 202.7 > Diff 10.4% 6.5% 11.2% 3.2% cal-exp > > Fres,cal 123.1 139.6 372.9 200.0 Wheeler/Medhurst > Diff 3.4% -5.5% 1.3% -1.3% cal-exp I concur with your calculations. > It seems, my coils are yet more happy with Wheeler/Medhurst, > however the precision of the experimental data have to be > considered. Regarding the instruments, I believe to be quite > precise (specifics can be supplied). The most of error probably > stems from the spacial situation, present, when measuring the > coils: capacitive influence of the surroundings! The B&W coil, > i.e., was tested in my living room, which is one floor above > ground level, and the top of my big coil only ~0.4m from the > ceiling. Agreed. In the case of the B&W coil, the lack of a well defined ground surface provides an ambiguous termination of the external E-field, so the coil is outside the domain of the formula. My attempts to model coils at high elevation have all failed dismally, due possibly to the poor definition of the return path for the external field - all were measured indoors. I'm still hoping that someone will setup a coil outdoors and high up over a good ground plane, so that I can see if the problem persists. Meanwhile I can only model reliably for b <= 1.0 and the formula is only regressed against data for 0.033 < b <= 0.5. The Sk-12cm which is a smaller coil, low down, should be quite accurate. However, for Sk-12cm, something is wrong: 22 awg = 0.6438 mm diam, so 921 turns spans 593 mm, this is longer than your coil. Perhaps you can look into this? Your coil Sk-Long is particularly interesting, as it falls into the large h/d category in which modeling predicts a resonant frequency some 10% higher than Medhurst. Your measurement falls in between the two, and I suspect that it may suffer some of the problems similar to the Sk-B&W, in that it is quite a large coil to be measured indoors. If it becomes possible to measure this coil in a large room or outdoors, over a reasonable ground plane, the result would be interesting. My prediction is that the absence of nearby walls and ceiling will reduce the external capacitance and raise the frequency to nearer that of the formula. I just ran Sk-Long through the precision model to obtain the following predictions for operation in an open space at b=0.5 over a ground plane radius at least 2m: Ldc=67.6 mH, Cdc=35.3pF f1: 155.9 kHz (Lee=45.7mH, Les=52.6mH, Cee=17.2pF, Ces=19.9pF) f3: 383.7 kHz f5: 544.9 kHz which unsurprisingly is close to the formula prediction. I also ran Sk-Long with walls introduced at radius 2m, and a ceiling at height 2.3m. The result is f1: 147.2 kHz which is close to your measured value. Clearly, the presence of walls and ceiling may well be responsible for the discrepancy with the formula. The Wheeler/Medhurst estimates seem to do OK at predicting your resonances. This must be accidental, since it takes no more account of the environment around the coil than my formula does. The large h/d regime, in which Wheeler/Medhurst errs on the low side, may be offset to some extent by that fact that the larger h/d coils are inherently more sensitive to the external capacitance, so that nearby walls and ceiling will depress the actual frequency somewhat more than for lower h/d coils. Hopefully as further measurements become available, this situation will be clarified. > BTW: Would you have perhaps at hand, a version of your function > fa = -94.6683*awg*awg*awg + 9000.55*awg*awg - 301175*awg + > 3.64056e+6 > beeing currently a function of awg, made a function of wire > diameter instead, like f(wd[m])? Measured values of wire diameter > could more easyly be introduced that way. You can use awg = 1 + log(7.348e-3/wd)/0.115943 and use this awg in the formula for fa above. Regards, -- Paul Nicholson, Manchester, UK. --

- Prev by Date:
**Re: Ancient Rectifiers** - Next by Date:
**Re: Spark Dissipation** - Prev by thread:
**Re: New formula for secondary resonant frequency** - Next by thread:
**Re: New formula for secondary resonant frequency** - Index(es):