On 4/25/05, Peter <plp@actcom.co.il> wrote:
> 
> Hi all, I have a small problem. I have a new thermistor and a new 
> thermostat I am working on. The thermistor is paired with a standard 
> thermometer. As I cycle the thermistor (between about 20 and 50 deg C) I 
> can see it does not go back to the original value. Just how much is a 
> new thermistor supposed to drift (in percent). It's a low cost unit but 
> not that low. I have worked with thermistors before and this one seems 
> way out of line. I see a 4% difference after a cycle from 20 to 50C, 
> coming back to 20C, and it takes ages (~10 minutes ~) to return to the 
> original value for the last 5 degrees (way more than the reference 
> thermometer glued to it). 


  I think you've got the answer already by a previous poster. The
thermometer is not a perfect measuring tool. It "eat" the heat.
 However I suggest you a trick: use cheap termistors. If you need one
then buy 20. Aging them by keep all at 100C for one week or more into
an oven. Then choose one and calibrate it. Will be perfect. When
calibrate, use a thermostat and do not expect
miliseconds in reaction time if a huge thermometer is glued on the
thermistor or if the thermistor is huge.

best regards,
Vasile 



That is enormous imho. I think that I have a 
> faulty part, but I would like to know if someone has seen such problems. 
> My circuit dissipates less than 1mW in the thermistor so that cannot be 
> the reason.
> 
> tia,
> Peter
> -- 
> http://www.piclist.com PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>

-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist