Below is a suggestion for a schematic showing an ADC input for temperature measurement using a 3‑wire PT100 RTD sensor:

1. Constant Current Source
• Use a constant current source (for example, an LM317 configured as a constant current regulator) to excite the PT100. This ensures a stable excitation current so that the voltage drop across the sensor is proportional to its resistance (and therefore temperature).

2. PT100 Sensor (3‑Wire Configuration)
• Represent the PT100 as an RTD resistor. One lead is connected to the constant current source, while the other two wires are used to sense the voltage drop.
• The additional (compensation) lead helps cancel out the voltage error due to lead resistance.

3. Signal Conditioning and ADC Input
• The voltage developed across the sensor is fed to the ADC.
• Optionally, use an op-amp in a buffer configuration or as part of a differential amplifier (if you need to subtract the extra voltage drop of the compensation lead) to ensure proper signal conditioning before the ADC.

4. Ground Connections
• Use the Ground component to interconnect all circuit ground nodes.

Implementation Notes:
• The current source should be designed to supply a known, low current (e.g., on the order of 1 mA to 2 mA) to minimize self-heating in the PT100.
• The output voltage (across the RTD) will be the product of the excitation current and the sensor resistance (which changes with temperature).
• If additional filtering is needed, you might include a low-pass filter between the sensor and the ADC to reject high-frequency noise.

Would you like to add these components and wire connections step-by-step to your schematic?