I have a resistance thermometer that outputs 4–20mA over 0–100°C. I can convert this to 1–5V with the use of a 250Ω resistor. My aim is to measure the voltage and scale it to the temperature and log it every 5 seconds to plot a graph. Would this be a project suitable for a beginner? Where do I start?
I think this is an ideal project for starting up with RPi.
I would buy an Analog-to-Digital converter (ADC), which can sample your voltage, and transmit the value to your RPi via a digital line (typically SPI or I2C).
For starting, I would recommend an SPI bus compliant ADC chip. For example, the product below has a nice tutorial for getting started with it on RPi:
A similar chip from another reseller: https://www.sparkfun.com/products/8636
If you prefer I2C bus (again, with a detailed tutorial): search for ads1015 in Learn section on Adafruit
Periodic logging & plotting I would do with Python, since it's fast to learn and a lot of tutorials/support is available throughout the web (e.g. instructables).
Sorry, i had to remove my web-links beyond the first two, due to my fresh account.
To convert 4-20mA values into read data values you will need readings at two known points, using these two points you will be able to calculate the slope (m). using this slope you will be able to calculate your real word readings at any given point of time. Here is an excellent article you can checkout https://ncd.io/how-to-convert-4-20ma-current-loop-to-voltage/