>>
I'm hoping to use an AD592 temperature sensor to *accurately* measure
temperature (+/- 1 degree C).  The device outputs 1uA/K and has a rated
accuracy of (+/-0.5 degree C).  Now, to measure the current produced by the
AD592 I am measuring the voltage over a known resistance value (~10K) using
a PIC.  Unfortunately, I didn't account for the fact that the PIC AtoD
really gives you a relative voltage (i.e. what percentage is the measured
voltage compared to Vref+).  I'm using a LM2940 to achieve +5V from a 9V
source, but the LM2940 actually outputs 5.4V (beyond the maximum value
specified in the datasheet) and will decrease as the 9V battery voltage
decreases.  Thus, I am left with no accurate way to measure the absolute
value of the voltage across the resistor connected to the AD592.
<<

You could use a zener or two to create a reasonably accurate Vref for the
A/D converter.  A better but costlier approach would be to use a voltage
reference chip to feed Vref.


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, olin@embedinc.com, http://www.embedinc.com

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