From: Greg Leyh
Date: Sun, 20 Oct 2002 11:28:17 -0700
Subject: Re: [TSSP] F A N T C: - It's NEW! - and needs some TSSP input
At 03:35 PM 10/19/2002, Bart wrote: >Hi Greg, > >With a single turn primary, the top and bottom heights can be equal as >long as the single loop is given a radius of r2 larger than r1. I had to >find some way to prevent impossible dimensions from running. When this >happens, geotc will cause a bailout, thus, I was writing validation for >every "possible" configuration. I ran into this very situation with single >turn loops, where we would want to make r1=r2, but this causes problems >elsewhere if h1=h2 at the same time. In order to run the single turn loop, >I wrote the validation to prevent an r1=r2 if h1=h2 situation. Thus, to >run the single turn loop, make r2 slightly larger than r1. Check the >single turn loop demo. There you'll find r1 = .5, r2 = .500001, h1 = 0, >h2 = 0. > >That's the way to do this at this time. I'll look into seeing what I can >do with the validation to allow this and still prevent bad inputs from >getting into geotc. I figured this would come up and glad it did. It just >confirms that I need to spend more time in that area. The r2=r1+ypilson rule seems reasonable. I'm not sure that anything really needs to be done, other than perhaps adding it as a footnote in the help window for 'Define Primary'? I'm trying out some impractical coil dimensions now, and I was wondering what the limits on physical dimensions should be for this algorithm, if any, to maintain accuracy. In particular I'm interested in calculating the inductance of a single turn coil, where the conductor diameter is small compared to the coil diameter. For this case, Wheelers' equations for a flat spiral and for a solenoid boil down to: L(uH) = R^2/8R and L(uH) = R^2/9R, respectively. For a single-turn coil 20ft in diameter with a 0.1" dia conductor: The Wheeler formulas yield 30uH and 26.6uH respectively. The Maxwell 3D 9.0 field simulator yields 51uH. Given the following inputs for the coil dimensions: Inside = 240 Outside = 240.1 Bottom = 0 Top = 0 Turns = 1 FANTC yields 66.44uH for the primary calculator, and 0.07mH for the secondary calculator. (BTW, the algorithm appears to not yield any results if the primary and secondary have identical dimensions; a silly case though, I'll admit.) To resolve the wide range in calculated results, I set out a 20ft diameter circle of RG-174 coax cable in the parking lot and measured the inductance of the outer jacket (~0.1" dia). The inductance meter gave 32uH, measured at 1kHz. Perhaps the measurement is skewed by physical factors, such as random bits of metal under the asphalt, although the test was done over a recently laid patch of asphalt with no metal remesh. Does this coil have proportions that incur high calculation errors?
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.