Abstract: An apparatus and method for mounting a sensor with strict orientation and insertion depth requirements in a process vessel or pipe section. The apparatus includes a lock block having a socket for receiving a plug disposed around a sensor inserted through an inner bore of the lock block. Reception of the plug in the socket controls insertion depth of the sensor in the process vessel. The lock block also includes a cam bore for receiving a cam used to rotationally orient the sensor and the attached plug. The cam is locked into position within the cam bore of the lock block by inserting a retaining pin through a retaining pin bore in the cam. During insertion and removal of the sensor through the sensor mounting apparatus, process isolation is maintained by an integral seal mechanism of the lock block and an internal isolation valve that fits within the lock block.