MWD Sensors Used in Directional Drilling Guide
All MWD sensors used in the downhole tool must be rugged enough to withstand the harsh environment. Only one of the systems currently available has the facility to change-out damaged components (sensor package/electronics) without tripping the whole bottom hole assembly out of the hole. The failure of one sensor may not necessarily mean that the tool has to be pulled out.
https://www.drillingmanual.com/mwd-sensors-directional/