On Tue, 7 Dec 2004 21:06:24 +0200 (IST), you wrote:

>
>
>On Mon, 6 Dec 2004, Eric Smith wrote:
>
>> Paul wrote:
>>> transfer my pid control into my solding iron and found
>>> such a good try.  With my solding iron been pid controlled, the
>>> temperature goes within 3 degree and give such perfect, small sodling.
>>> It is much better perforomance than expensive Weller products (it gives
>>> 20C deg moving normally). By the better controlling, I now can set my iron
>>> at 197 C and get all kind of benefit with this temperature.
>>
>> I don't know, but perhaps PID control is used in Metcal soldering
>> equipment.  They certainly seem to have much better temperature
>> regulation than anything else I've used.
>
>Afaik they use the same Curie effect as Weller/Cooper do, but unlike 
>Weller the sensor *and* the heater is the bit itself. This means that 
>temperature regulation depends on the Curie point (very sharply defined) 
>at a very small distance from the work (fractions of a millimeter 
>probably). F.ex. it should be possible for the left half of a 0.8mm bit to 
>be colder by 0.1 degrees C than the right and it to receive power from the 
>rf heater source, while the other half doesn't.

Once you have used a Metcal you won't want to use any other iron again. 

There is no control other than the curie effect in the tip heater - this is a slug of metal welded
to the back of the tip, surrounded by a coil excited by RF. The heater absorbs as much energy as
needed to maintain the temperature, and being a lump of metal has very low thermal resistance to the
tip.  
Most people don't need ultra-precise temp control, but what you do need is power on demand, quickly
without overshoot and this is exactly what the Metcal gives you - even relatively small bits can
solder large-ish terminals and groundplanes, and with the bigger bits you can do stuff like
soldering a TO220 tab to a groundplane easily without damage (OK you don't often need to do this but
it illustrates the capability).
There are 2 other major side-benefits- you can change a tip and be up to temp again in about 15
seconds, and the very compact heating arrangement means that you are holding the iron very close to
the hot bit, so control is very good, and the handle stays stone cold.
 
 

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