Electrothermal response testing more than a quality assurance tool

A simple engineering model of hot wire behavior was constructed based on the electrothermal parameters that can be obtained by the application of that nondestructive test technique. The model uses the data taken before the pyrotechnic charge is loaded on the wire as background data. The data taken as a loaded component is modified by the before loading data. The ETR data is combined with the auto-ignition temperature for the pyrotechnic and the restive heating capacity for the bridgewire to predict an approximate ignition time for the device. A modification of the procedure can be used to predict the no-fire level of the device. A reasonable estimate of the spread in ignition threshold currents at constant current can be obtained by applying the data spread in the ETR gamma values to the no-fire estimate. One of the major benefits of the model is that the temperature of the pyrotechnic mix and the bridgewire can be calculated and presented graphically. This visualization brings together many of the known facts about the electrically ignited system. The relationship between hot and cold firings, high and low current inputs, and the thermal properties of the ignition interface are easily seen.