From: "Terrell W. Fritz"
Date: Thu, 15 Feb 2001 19:43:11 -0700
Subject: Re: [TSSP] Top voltage testing
Hi Paul, At 06:55 PM 2/15/2001 +0000, you wrote: >Terry wrote: > >> Winding length = 26.125 inches >> Diameter = 4.25 >> #24 wire = 0.0201 diameter >> Turns = 1180? >> Rdc = 34.0 >> Ldc = 22.1mH >> Height off ground plane = 0.35 inches > >Putting these dimensions into the model gives > > measured modeled error >Rdc: 34.0 ohms 34.2 ohms +0.6% >Ldc: 22.1 mH 22.54 mH +2.0% > >(I used the measured Ldc, rather than the calculated, in what follows. >Are we seeing reduced Ldc due to eddy current coupling to the foil?) > >f1: 358.3 kHz 357.3 kHz -0.3% > >> Using the Tek 5100 probe on the top I get: >> F1 = 311.3kHz >> Iin = 0.20815mA >> Vtop = 7.9465V >> >> I calculate that the H/D is 6.1471 >> Vtop / Iin = 38168 ohms >> Zes = 19.5135mH or 88.3% of Ldc > >OK, I find that 3.11 pF of probe capacitance is necessary to reproduce >this f1: > > measured modeled error >f1: 311.3 kHz 311.3 kHz 0.0% Ctop adjusted to match >Zft: 38168 ohms 34903 ohms -8.6% >Les: 19.5135 mH 17.8 mH -8.6% > >Roughly speaking, the model predicts Les at 80% of Ldc, and you're >splitting the difference at 88% Ldc, > >Can you check that you have an f3 lurking at around 871 kHz for the bare >coil and 829 kHz in the probed coil. > >How come the base current dropped so much between the bare and probed >readings? > >Cheers, >-- >Paul Nicholson, >Manchester, UK. >-- I repeated the tests tonight and got the same results. Here are the answers to your questions. The pictures show the base current but you have to divide the vertical scale by 1000. The f3 of the bare coil is 883.1kHz. http://hot-streamer.com/temp/1-11noProbe.jpg The f3 of the Tek 5100 probed coil is 847.8kHz http://hot-streamer.com/temp/1-11yesProbe.jpg The reason the current is dropping with the probed coil is due to the Q of the coil dropping with the probe in place. Without the probe. http://hot-streamer.com/temp/3-4noProbe.jpg With the probe. http://hot-streamer.com/temp/3-4yesProbe.jpg The probe is rated at 10Mohm 2.75pF. Three factors may affect the coil's Zft. http://hot-streamer.com/temp/SmallCoilSetUp.jpg 1. The top terminal is a wire to a bolt with large steel washers 2. The ground plane is split but not perfectly, and it too uses large steel washers for the grounding stud. 3. The sensor box is near the base and may cause some distortion. I will play around with this stuff tonight and see if I can track down which one. Cheers, Terry
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.