Re: Formula for calculating temp in C

On Wed, 29 Jun 2005 10:41:08 +0200, Huub <hdotvdotniekerkathccnetdotnl>
wrote:

>Still assuming that I can use Steinhart - Hart for all thermistors:
>taken that A (diameter of NTC disc), B (width of NTC disc) and C
>(distance between the legs) are the physical measurements of the
>thermistor (Siemens NTC K164/1K5), I used metrics mm: A = 4mm, B = 1.5mm
>and C = 5.5mm. When I convert these to inches: A = 0.15748031", B =
>0.059055118" and C = 0.21653543".
>
>Tried in my workroom at 19C:
>
>Tc = (1 / (0.15748031 + (0.059055118 * ln(1686.64)) + (0.21653543 *
>(ln(1686.64)^3)))) - 273.15 = -273.139 C
>
>So, where do I go wrong?

They are not the physical dimensions of the thermistor. They are
empirical values determined by measuring at least three resistance -
temperature pairs and then solving the resulting simultaneous equations
for A, B, and C [*]. Modulo manufacturing variations, they are constant
for a given thermistor material and fabrication.

[*] or use a generalized non-linear curve fitting app, like Mathcad,
which makes the number crunching easy and also plots the residuals.

--
Rich Webb Norfolk, VA
.