Greetings waynb48 ...
we're going to have to know a lot more about your system in order to help you ...
what type of PLC ... what type of input module ... where are you connecting this potentiometer to the module (screw numbers, etc.) ...
big ticket item: there aren't any "relay contacts" associated with an analog input ... best guess: your program is looking at the input signal, making an EQUAL comparison, and using that logic to turn a digital output (relay) on and off ...
if my guess is correct, then you need to understand that the analog input will not be "stable" ... specifically, its numeric value will constantly be shifting by several "points" ... that's just the nature of the beast ...
one step further: since the value is constantly shifting, an EQUAL comparison will constantly be turning on and off ... again, if I'm guessing correctly, an LIM (Limit) instruction might be more in line with your requirements ...
tell us more about your system and we'll try to help ...