There's no need to linearize, calibrate, etc., all that matters for a
thermostat is that is keeps the same temperature (or close enough).
I don't think it could be reasonably done with a rheostat without
waiting a long time for things to settle. Would be just as worthless
as those soldering irons without temperature control.
I always say closed loop controls greatly improve the value of any
tool. We'd see them more often if people still knew how to make them
without an over-engineered approach that'll be way to expensive ;-)
If you have as much as $30 to throw at this you may as well save
yourself the bother and just buy the full-blown ready made PID
controller on ebay:
<
http://cgi.ebay.com/Dual-Digital-PID-Temperature-Controller-Kiln-Furnace_W0QQitemZ110475096602QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item19b8d4321a>
ST
On Wed, Dec 30, 2009 at 5:11 PM, RDHeiliger <rdheiliger@...> wrote:
> When I looked into using thermistors for laminator temp control, I looked at the maximum temperature spec of the thermistor. Few of them can withstand 170 ∗C. The glass bead type seem to be the only thermistors capable of going that high. They then get expensive and hard to find. Believe that is why Steven suggested pulling one out of an old laser printer fuser unit. Also, one needs to calibrate and linearize the thermistor output. Meaning, one needs to have some other accurate instrument to develop a lookup table. The same goes for using a thermocouple and an opamp. I personally decided that $30 for the AD595 and a thermocouple was worth not hassling with other methods.
>
> One could always just buy a rheostat and keep turning up the heat until one gets a good transfer and not worry about the actual temperature. Since a good transfer is the desired end result. Perhaps we some times over engineer things????????????
>
>
> RD
>