New to forum process problem

working on a type k thermocouple to an older acro mag then out 0-5 vdc into an older plc5.
this is monitoring in/out water temp from a chiller to process.
would like to make a filter or signal conditioner for the 0-5 vdc out to plc5.
we are getting a once in a while spike that looks like high process water temp.
have put scope on signal but have not been able to capture the problem, or see any noise.
Thank You Dean Downs