Hi Wagner,

Ah, I see. I didn't realize that they shot up in resistance so much as
temperature decreased. Thanks for the explanation. :-)

Sean


At 08:31 PM 12/2/99 -0500, you wrote:
>Sure, you are correct, it can also be done without any resistors. 
>
>The use of voltage dividers, mainly a resistor in parallel to the NTC is
>to help to flat the curve and reduce the peak of high resistances in
>very low temperatures, so you can gain in resolution.  Without any
>parallel resistor, the high resistence span is very high, you have a
>curve like this:
>
>*
>*
>*
> *
>  *
>   *
>     *
>         *
>                     *
>                                            *
>
>with a parallel resistor, you have something like this:
>
>*
> *
>  *
>    *
>       *
>           *
>               *
>                      *
>                               *
>                                           *
>
>and then, with the voltage divider, you can accomodate the exactly
>voltage span you need to your ADC circuit, without using any other
>front-gain amplifier, or something like that.
>
>By the way, if your software can do nice calculations rather than use a
>look-ahead table, you can use this formula:
>
>12th Degree Polynomial for NTC 44006 10k@25¡C.
>Functional range from -40¡C to +150¡C.
>X = Celsius Degree.
> 
>NTC_Ohms = a + bx + cx^2 + dx^3 + ex^4 + fx^5 + gx^6 + hx^7 + ix^8 +
>jx^9 + kx^10 + lx^11 + mx^12
>
>Legend:
>-------
>a = 28059.557
>b = -1358.1528
>c = 41.513538
>d = -0.77551934
>e = 0.005170511
>f = -1.999025e-006
>g = 2.345903e-006
>h = -7.3344661e-008
>i = 8.6221767e-010
>j = -4.3167639e-012
>k = 2.6210006e-015
>l = 5.3463809e-017
>m = -1.4179029e-019
>
>
>

|
| Sean Breheny                   
| Amateur Radio Callsign: KA3YXM 
| Electrical Engineering Student  
\--------------=----------------
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