The Arnold Engineering Development Center (AEDC) testing complex includes more than 50 wind tunnels, test cells, arc heaters, and other specialized test facilities. Of these, 27 units have capabilities that are unmatched in the United States, and 14 are unmatched in the world. These unique facilities create equally unique operating environments for instrumentation used for monitoring and control of test conditions. Several high flow-rate, supersonic wind tunnels utilize off-the-shelf angular displacement transducers (ADTs) for monitoring the position of 90° valves (i.e. butterfly valves) used to control the air flow-rate and bulk pressure during testing. Due to the high air flow rates in supply and exhaust ducts, there are significant structural vibrations to which the ADTs are subjected. These ADTs have experienced an unacceptably high rate of failure during testing. In the event of an ADT failure, alternative flow paths may, in some cases, be utilized. If an alternative path cannot be found, however, test operations must be suspended while the faulty sensor is replaced; leading to significant cost and schedule impacts associated with the down-time. This paper discusses an effort to understand the root cause of the ADT failures based on design information, and experience in the field. Several alternative mounting conditions were considered in order to reduce the vibrational loads acting on the ADT. A number of the alternatives consisted of utilizing different shaft couplings to couple the motion of the valve stems and the ADT sensor shaft. Experiments were performed at the University of Alabama’s Applied Controls Laboratory to test the effect of the different enclosures and shaft couplings. Preliminary results indicate that the shaft coupling, in particular, have a direct impact on shaft loads transmitted to the ADT. Test results and conclusions are presented.
