There are two reasons why the health code turns yellow. The first reason is that you move and stay near the key places where confirmed cases and asymptomatic infected people stay, and you may have contact with confirmed cases and asymptomatic infected people, so your health code is included in the yellow code range. The second reason is that if you have been to or passed through an epidemic-prone area and stayed for 4 hours, the health code may change and turn yellow or even red.
Whether the health code for going to Xi 'an and returning to Linfen on the same day will change depends on the epidemic situation at the destination.