36.3.3 Pressure Gauges Two PCB Piezotronics model 137A23 pressure gauges are placed in the camera plane for the validation of the shock wave incident pressure and positive time duration. Both sensors were mounted in a steel rod pointing in an axial direction to the detonator. Standoff distances from the energy source varied from 325 to 430 mm. At that range, and considering the explosive yield within the detonator, the sensitivity of the pressure sensors seems reasonable (100 mV/psi). The diaphragm was insulated using common black vinyl electrical tape to minimize possible signals generated by flash temperatures due to the passing of the shock front. Additionally, the bodies of the gauges were isolated from the ground by placing common black vinyl electrical tape in the contact surface with the steel rod. The two pressure sensors were connected by coaxial cable to a PCB sensor signal conditioner model 482C05. Both outputs were also connected to channel 1 and channel 2 of a Tektronix DP 3014 Oscilloscope where the signal provided by each gauge was recorded. Triggering was implemented from the firing machine and a signal differentiator which provides with a 2 V output to the lighting system, high-speed camera, and Oscilloscope. 36.4 Results and Discussion 36.4.1 Camera Results The events were captured by using a Phantom High Speed Camera v.711. Resolution of the image was set to 912 848with a sample rate of 9100 fps, and 0.294 us exposure (Fig. 36.3). Frame sequences for Number 6 and Number 8 detonators are shown in Fig. 36.4. The shock wave front traveling outwards has been highlighted with a white contour. As it is shown, the initial blast wave presents a sharp elliptical shape due to charge geometry. As the shock expands, the spatial divergence and Rod Mirror Nikon Zoom Lens with Rod Mirror Explosive charge Retro-reflective screen with frame Retroreflective Screen with fragmentation shield Strop Light with Collimating Lens Strop Light with Collimating Lens Phantom 711 digital video camera Phantom 711 digital video camera .... Fig. 36.2 Edgerton retro-reflective shadowgraph system, top view 284 V. Petr et al.
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