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[Amps] Muffin Fan on Swan Mark 1

To: <amps@contesting.com>
Subject: [Amps] Muffin Fan on Swan Mark 1
From: 2@vc.net (2)
Date: Fri, 26 Jul 2002 17:57:07 -0700
>2 wrote:
>>An IR thermometer,  a manometer, and some horse sense are more
>>trustworthy  than computer modeling -- i. e., if the thermometer says
>>it's too damn hot, and the computer app says it's not, it is.
>>
>
>They used to say that about antennas too, until MININEC and NEC became 
>available free to anyone who wants them. Certainly there are big 
>pitfalls in computer modeling, but antenna modeling has also shown that 
>"horse sense" isn't always reliable either. In the end, you need both, 
>in order to check each against the other.

So if horse sense yagi-uda design -- i.e., tuning for max fwd gain on an 
antenna test range - with element length/spacing experimentation produces 
more gain than the computer modeling antenna, one should assume that the 
fault is with the test range ?
>
>
>Exactly the same would apply to thermal/flow modeling if we had the 
>tools to try it.
>
>
>Unfortunately IR thermometers are notoriously UNtrustworthy, unless they 
>are calibrated for emissivity and - for this application - also have a 
>very small spot measurement size.
>
The better ones have a light-beam guide spot.

>The temperature readings depend on the emissivity of the surface. Cheap 
>IR thermometers assume a fixed emissivity of 0.95, which is a poor guess 
>for bright metal and even worse for glass. 

Black shoe polish is not costly.

>IR thermometers with a 
>variable emissivity setting need to be calibrated against the same 
>material at a known temperature (otherwise you can change the emissivity 
>setting and make the temperature read whatever you like).
>
>And then there's spot size. Even a good $500+ IR thermometer has quite a 
>large spot size, typically 0.5-0.75in across, and that's much too big 
>for a small object such as a tube pin. Specialized instruments with a 
>smaller spot size  are going to be much more expensive.
>
>Also the covers of the amp affect the air flow pattern, so they need to 
>be in pace for valid temperature readings. You point the IR thermometer 
>at the hot surfaces inside... exactly how?

Drill a hole, make the measurement, and tape the hole with aluminum tape.
>
>Sorry, IR thermometers have their uses, but determining tube pin and 
>seal temperatures probably aren't two of them (unless you're in the 
>giant tube league).
>
I am not a QRPPopath.

>I'm afraid it's back to temperature-sensitive paints, crayons and labels 
>- try Omega Corp in the USA for a very good selection.
>
>
>Earlier,  I'd asked:
>>>> Steve, do you know if there is anything freely available on the net for
>>>> heat and mass transfer modeling, equivalent to the way NEC-2 is freely
>>>> available for antenna modeling?
>>>>
>>>> //Ian, no I don't.  I honestly doubt there's anything very good available,
>>>> or my company probably would not have invested $60K in Flowtherm!
>>>> -WB2WIK/6
>
>Sorry to hear that...
>
>
>-- 
>73 from Ian G3SEK          Editor, 'The VHF/UHF DX Book'
>                           'In Practice' columnist for RadCom (RSGB)
>_______________________________________________
>Amps mailing list
>Amps@contesting.com
>http://lists.contesting.com/mailman/listinfo/amps
>


-  R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K, 
www.vcnet.com/measures.  
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