Sensor Linearization

[Todd Knighton]

peter paul fenske wrote:
> 
> Hi Folks:
> Tnx to all lending me a hand.
> Been looking through the archives but yet to find a proper discussion
> on sensor linearization.
> The inclination is to accept the Map sensor data as well as the Tps
> as they are linear even though there is a loss in range.
> One problem remaining is the MAT and the Coolant Temp Sensor.
> Going by service manuals and using a 1.2 K pullup this gives quite
> a nonlinear temp vs voltage.
> The question I have for the good folks is how do you linearize the
> sensor. Or is it necessary?
> One tacky piece of hardware is to switch in two resistors one for
> each range which would tend to give some linearization.
> Software wise one could use a lookup table. This would require close
> to 255 entries. Not really but quite a few. The other way is a search
> through a table and pick the data closest to the value measured.
> And the third is to use a smaller table, say 15 values for a search
> or a lookup and then interpolate.
> What I am trying to get is linear numbers between 0 and 255 for
> a temp range of about -40 to 250 degrees.
> Tnx again everybody: peter
> 
Peter,
	Bosch uses a cute little 12 position NTC sensor linearizeation 
table that does a real good job, I've checked it.  It ends up running 
linearly from -30F to 275F from 0 to 255 A/D. If it helps its:
(04 0C 	- 04 07 08 0F 1A 35 1C 1C 10 07 03 16	Position
	- 02 13 25 34 48 5F 89 A2 C3 E0 F3 FB   Correction)

Plotted out, it looks like a straightened out "S" curve.  The way Bosch 
reads it's maps is kind of strange though, from the top down on this 
one.

Good luck,
Todd Knighton
Protomotive Engineering
Email: knighton at concentric.net

P.S.	Also working on Idle stabilization routines for Bosch stuff, 
what a pain, any insight on what you've tried might help.