[Homeroast] heat gun method

Bill S. wsmailmagnet at gmail.com
Wed Nov 24 13:30:27 CST 2010


I like your (PID) thinking, but you are miles ahead of me technically.  It
seems that you would want a temperature reading that doesn't fluctuate
rapidly, to keep the PID's output constantly moving in the right direction
(versus the PID trying to correct for a temporary temperature reading in the
wrong direction).  I have found that a probe for a contact thermometer,
buried in the roasting beans is consistent, even with manual bean
agitation.  One problem that you can have with non-contact thermometers
(depending on the roaster) is chaff accumulating on the bean surface you are
shooting.  That will dramatically throw your temperature reading off.

The S.M. digital thermometer probe that I use came with a bare bulb attached
to high-temperature wire.  I epoxied this inside an empty stainless steel
ball point pen refill, with both ends off.  When mounted with a rigid
fitting inside the roaster, this remains in the center of the bean mass, and
the SS probably provides some temperature stability giving constant
readings.

BillS.

On Fri, Nov 12, 2010 at 4:03 AM, Allon Stern <allon at radioactive.org> wrote:

>
> On Nov 11, 2010, at 12:30 PM, Bill S. wrote:
>
> > At about the same point at which you are, I decided to buy a non-contact
> > infrared thermometer. Most are good to 1000F, and I have found mine to be
> > accurate in any roasting method where you can see (shoot at) the roasting
> > beans.  It has also been useful for home projects where I needed to know
> the
> > temperature of a surface.
> >
> > I addressed the air-vs-bean temperature issue by putting the probe in the
> > center of the bean mass (using SM's digital thermometer, in a homemade
> air
> > roaster, using a HG).  This way, the hot air hitting the probe has been
> > through half the beans, the beans are contacting the probe, and the
> airflow
> > over the probe is "average".  I compared readings from my non-contact
> > thermometer with the probed thermometer, and found that the tempeatures
> were
> > consistent enough for me to rely on the probe.
>
> I've thought about setting up a heat gun with PID, using an infrared
> thermometer as the temperature input (linear voltage or current).
> I just wonder how well the PID algorithm, as implemented in the industrial
> controllers I have, will deal with the variations induced by a hand-operated
> method, whether it will compensate adequately for them, or will be thrown
> off the rails.
>
> Heck, I could just get one of these
> http://www.sparkfun.com/commerce/product_info.php?products_id=9813
> and implement the PID algorithm on the microcontroller, plus an LED output
> to show process and measured temperatures.
>
> PID library here: http://www.arduino.cc/playground/Code/PIDLibrary
>
>
> -
> allon
> _______________________________________________
> Homeroast mailing list
> Homeroast at lists.sweetmariascoffee.com
>
> http://lists.sweetmariascoffee.com/mailman/listinfo/homeroast_lists.sweetmariascoffee.com
> Homeroast community pictures -upload yours!) :
> http://www.sweetmariascoffee.com/gallery/main.php?g2_itemId=7820
>


More information about the Homeroast mailing list