Introduction to ionization pin probes to measure detonation velocity

Detonation velocity can be measured by different methods. Earlier two probes of isolated twisted copper wires have been used to measure the time the detonation front uses for a predefined distance. The drawback with this method is that if one of the probes fails registration, no result is obtained. To increase the probability to get a velocity determination, we have investigated the possibility to use a more robust method with probes of ionization pins. In addition, ionization pin probes make it easy to increase the number of measuring points. The ionization pin probes we have tested have been prepared from a semi-rigid coax cable with an outer conductor of copper. In addition to the probes, a switch box with ten channels and one trigger channel has been built. An oscilloscope has been used to register the arrival time of the detonation front at the different probes. Tests of the method have been performed on a detonating cord and pressed charges of HWC (RDX/Wax/Graphite). Twelve probes have been tested out. We obtained registration on the oscilloscope for eleven probes at the expected times. The twelve probes were placed in three test items with four probes in each. The experimentally obtained detonation velocities both for the detonating cord and the HWC charges were all as expected. The values were 7291 m/s for the detonating cord, 8387 m/s (φ = 18.6 mm) and 8422 m/s (φ = 31.8 mm) for the HWC charges. The time signals we obtain have some oscillations. However, there is no problem to separate the arrival time of the detonation front for each probe, and the start time is unambiguous defined.