Fail detection is inherent to 4-20mA. When the input sensor is at minimum value, you should see 4mA. If there is a fault (broken wire, broken sensor, etc), you should see 0 mA. Your V200-18-E2B module has 10-bit resolution, so you should see a value between 204 and 1023 in the MI assigned to the analog input. In your ladder code, just look for a value that is outside of that range to trigger your fault detection action. I would give it a little margin for error (maybe 190-1030) and also include a short timer to avoid false positives.