A method of installing a temperature measuring device inside a reactor tube while filling the tube with catalyst is provided. The method includes inserting a positioning system, including a single inflatable bladder connected at a central location to a centering ring, into a reactor tube, the reactor tube comprising a distal end and a proximal end. Then inserting the centering ring around the temperature measurement device. Then locating the positioning system at a first predetermined distance from the distal end, and inflating the single inflatable bladder, thereby centering the centering ring and the temperature measurement device within the SMR tube. Then introducing catalyst into the SMR tube, thereby enclosing the temperature measurement device in catalyst.