Re: Formula for calculating temp in C

Rich Webb wrote: 
On Tue, 28 Jun 2005 20:10:45 +0200, Huub <hdotvdotniekerkathccnetdotnl>
wrote:


Rich Webb wrote:

On Mon, 27 Jun 2005 19:19:58 +0200, Huub <hdotvdotniekerkathccnetdotnl>
wrote:



Hi,

Is there any formula for converting a given resistance of the (Siemens) NTC K164/1K5 into temperature in Celsius? I'm not familiar with components, but I need to use it in software. 


You don't give enough information. How precise does your conversion need
to be? A simple linear approximation works just fine for some ranges and
for some applications. A second order curve handles many others.

For a more precise curve fit, search for the Steinhart-Hart thermistor
equation.


This formula gives 1/T with T in Kelvin. When I rework this to Celsius by (1/(1/T))-273.15 I get a rediculous temperature in Celsius. Hence, I suppose I'm doing something wrong. Can you tell me how I should do it? 


Don't assume that because S-H is the "best" approximating formula that
it's appropriate for real world use. Do you really need (and can you
afford the computational burden) of a 0.1 degree approximation? What's
the spec'd accuracy of the thermistor and associated components?

For A = 1.139456E-3, B = 2.323002E-4, C = 9.579158E-8, and R = 10000
then 1/T = 298.164 and Tc = 25.014. It's just plugging in the numbers.

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?
.

Relevant Pages

  • Re: Formula for calculating temp in C
    ... Is there any formula for converting a given resistance of the NTC K164/1K5 into temperature in Celsius? ... What's the spec'd accuracy of the thermistor and associated components? ...
    (sci.electronics.components)
  • Re: Formula for calculating temp in C
    ... Is there any formula for converting a given resistance of the NTC K164/1K5 into temperature in Celsius? ... A simple linear approximation works just fine for some ranges and ...
    (sci.electronics.components)
  • Re: Formula for calculating temp in C
    ... Is there any formula for converting a given resistance of the NTC K164/1K5 into temperature in Celsius? ...
    (sci.electronics.components)
  • Formula for calculating temp in C
    ... Is there any formula for converting a given resistance of the (Siemens) NTC K164/1K5 into temperature in Celsius? ...
    (sci.electronics.components)
  • Re: Formula for calculating temp in C
    ... >Is there any formula for converting a given resistance of the (Siemens) ... >NTC K164/1K5 into temperature in Celsius? ... NTC thermistor functions are somewhat complex, and it is usually more efficient to use a lookup ...
    (sci.electronics.components)