[AMPS] more resistor measurements

[Rich Measures]

>Dang it, now you got my curiosity about this resistor thing...
>
>I measured 3W metal oxide film resistors from DigiKey, cause I happen to
>have some. These values were measured on the Hp4193A vector Z meter, with
>about 3/16 inch leads on each side to the fixture. Sorry to you metric (SI)
>readers. I measured 5.1, 10, 15, 20, 30, and 51 Ohms. If someone sends me a
>higher value or different brand, I could add it to my data. This is the
>kind of stuff I wish Digikey, Mouser, Newark, Allied, Farnell, and all
>should publish in their catalogs, instead of saying "non-inductive design".
>That's pure BS, sure they are not wirewounds, but certainly NOT non
>inductive.
>
>I put together the data in a 6 page spreadsheet, with the formulas to
>convert impedance |Z| and phase (A) to Rs and Ls, which should be the model
>for a resistor I think. Rs = |Z| x cos A,  and Ls = |Z| sin A /(2 x pi x F)
>
>If you want a copy, it is in Excel worksheet format, for Office 98 (from a
>Mac). However, I can also send it in the older Excel formats. 

I use the Mac version of Excel 3.  I would appreciate receiving a copy of 
your worksheet, John.  
-  thanks

>In this worksheet are 6 plots of the Resistance and Inductance for each 
resistor,
>for every 5 Mhz from 1 to 100.  The lowest value had the highest
>inductance. But as they increased, the L always showed a dip at 5 Mhz. And
>were higher at 1 Mhz. I am suspect that it is a systematic error of the
>4193A probe residual L and R. They are published and in the range of the
>low measurements. Also, I could probably look up the error specs and find
>that it is worse off at low impedances, like 5 to 10%. So that could
>explain why 5.1 Ohms is SOOOO different. Any other explanations to hear?
>
5.1 ohms could be the highest value of metal film [MF] resistor that they 
make.  Higher values may be made of metal oxide film [MOF].  (note:  MF 
typically has a shiny surface, while MOF typically has a dull surface.)
  
>For those who cannot bring up the spreadsheet or don't care, but want to
>know how it compared to N5JA or W8JI's measurements (different techniques),
>here is a summary of my Rs/Ls in that order (Ohm/nH):
>              5.1 Ohms    10              15                20
>30                   51
>1 Mhz     5.6/60     10.8/27     15.6/26      20.4/28.3       30.8/25.7
>50.9/28.3
>10         5.7/59      10.8/24    15.6/23.9    20.4/23.9       30.7/22.2
>50.7/19.7
>30         6.13/58    11/24.6     15.7/24.4   20.6/24.2       31/22.8
>51.1/19.4
>50         6.6/57.4   11/24.2     15.9/24.2   20.7/23.8       31.2/22.4
>51.3/18.9
>70         7.1/57.1   11.1/24.1  16/24.2      20.9/23.8       31.5/22.6
>51.4/18.7
>100       8.2/56.8   11.3/23.9   16.1/23.7   21.1/23.4      31.6/22
>51.6/18.2
>
>The reason it is nice to sweep the whole range for each R, is to observe
>that it is indeed flat and doesn't exhibit some resonances, in this case
>all behave as inductive resistors up to 100 Mhz. You can also see the
>variation (mostly increasing) of the high freq resistance. Wish I could go
>higher but....
>
>By the way, this compares to the ballpark values posted yesterday, and
>these are the 3W smaller resistors.
>
>Please let me know if you want the data/plots emailed. Also, I haven't
>forgotten the folks that inquired for a paper copy of the old Philips
>article on pondermotive bending of filaments when arcs occur. It's just
>that I've been slightly swamped with getting an amplifier finished and
>trying to get one up on old Murphy.... (impossible)
>
>I remember doing an experiment in Radio Engineering Lab at Va Tech, under
>Dr. Herb Krauss (he cowrote the book Solid State Radio Engineering), in
>which we found that 100 Ohm carbon comp resistors were the most purely
>resistive resistors. Now I cannot remember if it was 1/2, 1 or 2 Watt! 

The shortest ones would be the 1/2w size.  

>But we just built a power resistor ourselves (2 weeks ago), and wanted a 
really
>low L or C 0.1 Ohm resistor, that can handle about 35 Amperes at 5% duty
>factor at 5600 KHz. We started with Cesiwid (globar/carborundum types),
>with 10 each of 1 Ohm units in parallel. They were not good, very
>inductive. 

However, the Cesiwid rep told me thay could slice off short lengths of a 
tubular extrusion and come up with sub-9-nano-H  resistors.  

>We settled on buying 100 real 1/2 watt carbon comp resistors at
>10 Ohms each, and soldering them between two pieces of copper punched at
>0.1 inch spacing like vectorboard. It was time consuming to build, but it
>is one sturdy and fairly good resistor. I realize that I could have located
>some power chip resistors to do this, and soldered them in parallel, but
>the leaded R's (which cost me almost 50 cents each!) seemed to be fine and
>quick to get. Didn't even consider the Metox film types, as we prototyped
>it with carbon comps. Wonder how the 3W guys would have worked?
>
depends on the value.  The Matsushita MOF 3W-rated, 10 ohm R appears to 
have fairly low-L.   In free air at room temp., it will dissipate 12w for 
one-hour. [11v] 
-  later

>John
>K5PRO



Rich...

R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures  


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