Dynamometer Calibration and Usage
NAVAL SURFACE WARFARE CENTER CARDEROCK DIV BETHESDA MD
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This report describes a potpourri of information concerning dynamometers that has been in use by various groups within the Maneuvering and Control Department of the Hydrodynamics Directorate. Because these transducers are complex devices requiring care with their calibration and usage, the authors felt that the important details should be recorded and made available to others at the Center. Following a basic discussion of the operation of the transducer and the need for an interaction matrix is a suggested calibration procedure that will yield data that completely describes the six degree-of-freedom parameter space of the unit. Subsequent sections describe numerical methods for the derivation of the interaction matrix from calibration data. The first of these methods is a Least Squares solution for the interaction matrix, and the second is a generalization of the first method that allows weighting of the data. Other topics include a method for transformation of an interaction matrix determined relative to one coordinate system into an equivalent interaction matrix relative to a second coordinate system, and a technique for normalizing the interaction matrix. Additional complications arise when dealing with rotating dynamometers and such topics as determination of the offset angle, and weight and zero compensation are investigated. One may wish to use two dynamometers in tandem to determine forces and moments about a common reference point the equations required for such operation are described in detail. A discussion of data uncertainty is incorporated, and finally, an appendix is included which describes how interaction matrices obtained from a dynamometer manufacturer were found to be in error, and how the methods described in this paper were used to detect and correct the errors.
- Electrical and Electronic Equipment
- Marine Engineering