@Dodo88 said in Reed Contacts with Distance?:
can i find out wich resistor is build in
Well, possibly you can measure it if you have multi-meter at hand. Anyhow, you can also try to connect a resistor as described above. Did you try this already? Btw, I don’t think the sensor has a built-in resistor, however, you want to try with a small value first, say 1K. Also the capacitor might help as suggested. Moreover, you could also try a different cable, e.g. use a shielded cable (connect shield to ground in case).
"It always takes longer than you expect, even when you take into account Hofstadter's Law.", Hofstadter's Law