Let me give you an example, a thermal resistor, always give him a current of 1mA.
When the temperature is 80 degrees, the resistance is 1k ohms, and his voltage is 1V.
And then we know that 1V corresponds to 80 degrees.
If the AD converter is 12-bit, its value is 0-4095. If the input range is 0-5v, then 1V corresponds to 819.
At this time, we know that the voltage corresponding to 819 is 1V, and the temperature corresponding to 1V is 80 degrees.
Can this process be understood?
To complicate matters, the actual parameter x is measured, such as the temperature value. Through the sensor principle and design circuit, the voltage of the circuit can be obtained as u=f(x), and then the output of AD can be converted to n=g(u) through AD.
And once we actually get n, we can find the inverse function all the way to x.
U =g '(n),x=f' (u)
In general, g is just a linear stretching relationship, and finding the inverse function is very easy. If you don't understand, do the math yourself.
f is a bit complicated, and the circuit part will master the bridge circuit and the operational amplifier. The sensor itself may also be nonlinear, which is generally fitted by polynomials of finite order, or by algebraic interpolation. You get a simplified formula and then you find the inverse function.