[Amps] Centurion cooling improvement ideas for AM service

[R.Measures]

On Aug 26, 2004, at 12:18 AM, Ian White, G3SEK wrote:

> Will Matney wrote:
>
>>> The Fluke Model 61 is $109.  It shines a laser beam where it is 
>>> measuring the temp.
>>> http://www.newark.com/product-details/text/CD121/49571.html
>>>
>> Will miracles never cease! I never thought I would see the day a 
>> Fluke instrument would be that cheap. I figured that being a Fluke 
>> would have been $350 to $450 dollars. Thanks for the info on this 
>> Rich, I may just get one of these myself! The model 65 is only $289 
>> and has memory with temp conversion. The 61 is really all ones needs 
>> without getting extras. That would come in handy around the house 
>> checking for heat or cooling leaks around windows and doors. I would 
>> like this for not only checking tube temperatures but the temps on 
>> transformer coils and cores.
>
> Sorry, but miracles are still in short supply. IR thermometers have 
> several weaknesses, and all the cheaper models (including the Fluke 
> 561) have an additional major problem: they assume a fixed value for 
> the thermal emissivity of the surface they're looking at. If that 
> fixed value is incorrect, the computed temperature reading will be 
> incorrect too.
>
> The Fluke 61 assumes 0.95, which is good for many kinds of dull 
> surfaces, but the emissivity of bright metal surfaces can be 
> significantly lower than that, so the meter will read low too.

Ian -- Agreed, however, the solution is:   do not have the dull-gray 
anode stem chrome-plated on the 3-500Z.
>
> You can of course calibrate the meter by pre-heating a similar surface 
> to a temperature that you're also measuring some other way, but on a 
> fixed-emissivity instrument the temperature error will not be constant 
> - the error itself will vary with temperature. With a more expensive 
> variable-emissivity instrument, you still have to do the same 
> calibration, but there is an emissivity setting that you can adjust to 
> make the meter show the true temperature; it will then read true 
> across the whole range.
>
> However, the three types of measurement that we're most interested in 
> happen to be the three very worst cases for any kind of IR thermometer 
> - even the most expensive.
>
> 1. Air temperature: you can't measure it with an IR thermometer - 
> you'll always see the temperature of the surface behind the air 
> current. Alternatively, you have to put some small object into the air 
> current so it takes up the same temperature as the air, and then 
> measure that object.
>
> 2. Shiny objects: anything that looks like a mirror has a very poor 
> emissivity. It also *is* a mirror, so the IR energy may be coming from 
> something else, reflected by the object you're trying to measure. (I 
> guess a laser pointer might be a good warning that this may be 
> happening.)
>
> 3. Glass - even worse than metal!
>
> All these weaknesses come together if you're trying to measure the 
> anode temperature of a 4-Something or a 3-500Z. *You* can see the 
> anode glowing behind the glass, but what the IR thermometer sees will 
> be anybody's guess.

The Fluke 61 has a laser beam pointer.
end
>
Richard L. Measures, AG6K, 805.386.3734.  www.somis.org