I wish to make a set of temperature measurements inside a relatively inaccessible box.
The measurements can be made using Pt100 sensors - platinum Resistance Temperature Detectors (RTD) with a resistance of \$100\Omega\$ at \$0^{\circ}C\$. The change in resistance over \$80^{\circ}C\$ is around \$30\Omega\$.
I want to digitize this result within the box. I'm currently looking at microcontrollers like this STM32F373 model, which includes (several) 16-bit ADC.
To minimise the self-heating on the RTD, I want to minimise the current used. To make an accurate measurement, I would seem to need a constant current source. Wikipedia suggests several arrangements, at least one of which is given as an answer to this question - Zener Diode Current Source.
How can I go about arranging a known constant current, with only a constant voltage source?
Should I build a circuit similar to the 'Zener Diode' question, separate from any circuitry near the microcontroller, and then just pass the sense leads to the analogue input?
Is there a simple trick to precondition the voltages to lie within a good range for the ADC? Seemingly a combination of gain to scale the range to fit \$V_{DD} = \frac{30\Omega}{I_{const}}\$ along with a constant offset from another circuit would be appropriate - but perhaps this is just because I'm stunningly ignorant.