A compact electrocontact probe system for real-time direct free surface velocity measurements in blast experiments

Conventional electrocontact instruments found in the literature are primarily designed for detonation velocity measurement. This work presents a novel low cost electrocontact probe system for direct measurement of free-surface velocity of metallic plates in blast experiments. The setup includes four probes connected to a custom-designed electrical circuit that triggers an oscilloscope through an electrical discharge of capacitors upon transition from open to short circuit, recording the exact time of contact between the target plate and probes on a single oscilloscope channel.Validation of this system was first performed in a medium-velocity test using five 0.5 mm brass sheets separated by insulating foil, submitted to the impact of a fired nail, fired by a powder-driven nail gun, reaching a penetration velocity of 60 m/s. The system was then applied in explosion chamber blast tests, where free-surface velocities up to 470 m/s were recorded on 500×500 mm 2 stainless steel plates impacted by a water blast wave generator made from a water container with an emulsion explosive charge inside.This method enables direct, real-time velocity measurement without complex post-processing and can bescaled to multiple measurement points by adding more probes and more oscilloscope channels.