>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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