Sensor Linearization

[FIScot at aol.com]

In a message dated 96-06-13 05:26:24 EDT, you write:

>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?

If you have lots of PROM space, one fast way (cpu cycle wise) to linearize
the MAT or CTS is to have a 256 byte look up table representing the complete
temp range of the sensor.  Get the A/D result for the sensor, and move it to
ACC B.  Point the INDEX to the start of the table, add ACC B to the INDEX,
and get the value at the new INDEX loc that represents the temp of the
sensor.  Quick and easy once you establish the table.

As far a the MAP sensor, I have plotted the output of several MAPS, using a 5
volt ref, a voltmeter, and a hand held vacuum pump.  These things are amazing
linear!   They don't go all the way to 0 volts, or all the way to +5 V, so
the output only uses a portion of the available range.  Just subtract a
nominal minimum position from the output to get to zero, then scale what
would be the max range of the sensor to be the max output that fits in '00'
to 'FF'. 

Scot Sealander  FIScot at aol.com