Detection methods for locating obstructions in blown optical fiber ducts

Currently obstructions in blown optical fiber (BOF) tubing (microducts) are found using the ball bearing test (BB test) as described in test method 6H1 of MIL-STD-2042. A 4.5 millimeter (.17 inch) BB is launched down the entire length of the tubing (6 mm ID) with air pressure ranging from 50 to 100 psig. The BOF tubing is considered obstruction free if the BB can traverse the entire length of the tube. If the BB does not pass through the BOF tubing, there is an obstruction at an unknown location. Determining the position of this obstruction is time consuming, and if unsuccessful the entire BOF tube has to be scrapped. There would be a cost saving benefit if an accurate way of determining the location of the obstruction was found.