End-to-End Mechanical Calibration of Strain Channels in Dynamic Health Monitoring Systems

Abstract

The U.S. Air Force invented a calibration technique that allows one person to perform multiple, mechanical end-to-end calibrations of structural dynamics measurement systems. In Order to define the vibrations and acoustics environment, often an aircraft or engine structural health monitoring system collects airframe or engine structural integrity data. A recommended practice is to perform an end-to-end mechanical calibration of the system. This means a full calibration of instrumentation from the physical input to the transducer to the output where the analog or digital signal is normally analyzed. It is difficult to stimulate mounted and embedded transducers with a known physical input, especially strain gages bonded to a structure. This new technique uses a remote control structural exciter (RCSE) to stimulate transducers in structures, with a measurable input level, and the output signal is communicated to the data storage device of the structural health monitoring system. The Air Force demonstrated this patented technique by using accelerometers in the laboratory. This paper investigates this new technique to evaluate and calibrate strain gages mounted on structure. A reference piezoelectric strain gage measures the input. A typical system may include dynamic strain gages connected to a battery operated data acquisition system. This paper describes the invention and looks at potential field applications to insure data integrity of strain data in structural health monitoring data acquisition systems on aging commercial and military vehicles. Also, the paper describes a planned design of experiments to evaluate the use of remote control structural exciters for mechanical end-to-end calibration of strain gages in measurement systems.