thermistor III

Martin Czech martin.czech at intermetall.de
Fri Jan 9 10:34:54 CET 1998


Using the said NTC from my last mail "thermistor II" with parallel res
1950 Ohm (for adjusting "steepness") and serial res 3900 Ohm (for
adjusting resistance "offset") as uper leg and 100 Ohm as lower leg
gives about five times smaller temperature error of the exponentiator
current over a temp range from 10C to 90C chip temperature.  This
includes 2% error of NTC curve, and 5DEG mismatch of NTC and actuall
chip temp. An ideal matched pair is assumed, and other sources of error
are neglected.

I can confirm : As Rene said, it would  help a lot.  

I don't know how good a number of NTCs will match. Farnell offers some
with specified matching. (They also have PTCs thickfilm resistors with
+3000ppm/DEG, has anybody measured these ?).

I'm really thinking about compensating my exp/lin VCA with such 
devices (expo as well as log circuitry).

m.c.

------------------------------------------------------------------------
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