I'm working on a design for a multi-sensor temperature alarm for a greenhouse.
I plan on using PTC thermistors as the temperature sensors as I have a few 1k PTCs lying around.
Can I connect the PTC to a very long (about 20-30m) cable and then use a capacitor in parallel on my PCB as a low pass filter set to a couple of Hz (i.e. 10Hz or lower) and then feed the signal into a window comparator? Will this work or is the long cable and noise a problem? For the cable I will try to find something like shielded twisted pair, if that's available and cheap.
I have looked around on the internet but have not found any info for more than like 5-10m of cable length, for which the info suggests twisted or shielded cable and a capacitor to form a low pass filter.
Edit: I have not yet created a full schematic or even planned every part of the device. Anyways:
As requested I quickly drew a schematic. This is not in any way final, but it is roughly what I was thinking about. The output would drive some other circuits, but that is not relevant here. Also the parts are not neccesarily going to stay the same, as I am just at the very beggining of this project. The PTC is a KTY 81-110 for which you can easily find a datasheet online and that is the only part that I would like to keep as it is, because I have some of them lying around.