The Development of a Miniature, High Speed Telemetry System For Dynamic Stress Analysis

Twenty years ago diesel engine manufacturers guaranteed and expected 50,000 to 100,000 miles of trouble-free engine operation. Today’s standards are set at 250,000 to 1/2 million miles operation without a major overhaul. These continually expanding requirements have created new problems for the design engineer. To be competitive and to develop an efficient, long life product the design engineer must have a more complete understanding of his product’s capabilities. He can not always rely on calculations or instinct but must confirm his theories and designs by conducting more comprehensive physical tests. Many months of field testing often was required to evaluate the effect of a single design modification on the durability of the part. If a means could be found to measure the stress levels in these components under actual operating conditions in the laboratory answers could be obtained in a matter of days rather than months. A lack of commercially available test equipment suitable for obtaining these measurements resulted in a decision by Schwitzer to develop such equipment. By the end of 1963 a high speed telemetry system was in operation that could accurately transmit dynamic strain signals from a gas turbine wheel rotating over 100,000 rpm in a 1400 deg F environment. This paper reviews the several phases of this project and describes the telemetry system that finally evolved.