I'm looking for a little direction or recommendations in how to select and implement a low-pass filter in software as my background in signals and systems is quite weak. In particular, I'm interfacing to an analog input that accepts either a standard 0-10 V or 4-20 mA signal (circuit can be physically switched) and am concerned about noise that can be expected from running the signal wires over 100 ft adjacent to wiring for lighting systems and other power electronics. The initial idea was to simply have an adjustable window size for averaging samples, but it appears that the time period needed to effectively combat noise in some scenarios also introduces significant lag as well.
Ideally, I would simulate the scenario above with a physical setup and take extensive measurements before starting this, but time constraints make it difficult. I did a quick search for a web tool that generates coefficients and the first thing that Google brings up is http://t-filter.engineerjs.com/. Is this a good place to start or is guess and test a waste of my time without doing more research? Is there a particular type of digital filtering topic that I should direct efforts to researching?