The terms 'police inspector' and 'constable' are used in connection with the police in England, Canada, Australia and New Zealand (and possibly other countries. A constable is a police official of the lowest rank, while an inspector is of the middle rank. [Someone from England can correct me on this - this is what I remember from living there, but I could be wrong.]

police inspector is a senior officer （比较有经验的警察叔叔） constable is a police officer of the lowest rank (等于中国巡警或者黑猫警长的小弟)