1. Put it in a loop. If the sensor has some manner of feedback (such as
adding another transducer to feed back to the sensor, etc.), sufficient
negative feedback will linearize it. Baxandall(?) covered this almost a
century ago (and likely, mechanical engineers even earlier).
2. Construct an inverse function, perhaps out of piecewise functional
blocks (op-amps with lots of diodes and resistors), or components with
specific properties (e.g., FET for squared terms, silicon junction for
exponential terms) to effectively neutralize the sensor's own nonlinearity.
3. Combine 1. and 2., by using a (known to be linear) transducer to excite
an identical isolated sensor, enclosing this in a feedback loop. The error
signal from this sensor feedback loop is the exact inverse function of the
sensor's nonlinearity (within reason). Add the sensor's signal to this
function block and you will get a linear output.
#1 and 3 have relatively slow response time, but can be arbitrarily
accurate (the limiting factor is how much feedback you apply and the delay
time you can allow for it to settle to that accuracy). #1 may not be
practical, especially if your pressure sensor must connect to other things;
connecting pressures "in series" may not be very practical. #2 is the
fastest (effectively instantaneous), but must be tediously adjusted to
accuracy.
If you're digitizing the signal anyway, you might as well calibrate your
own correction table for the sensor, forgoing the analog solution. Sensor
voltage maps to address in memory, which then maps to the corrected value.
What's more, if you have a linear sensor, you could generate the conversion
easily enough automatically. (This of course begs the question, why don't
you have a linear sensor to begin with? I'd assume you have some sort of
standard somewhere.)
Tim
