V.O.D. measurement methods
The three measurement families used in laboratory and field V.O.D characterization, with their respective strengths and operational limits.
Point by point fiber optic methods
Plastic optical fibers are inserted at known distances along the explosive column. As the detonation wave passes, the light flash it emits reaches each fiber tip and is conducted to the recorder. Dividing the inter fiber distance by the measured time of flight returns the average V.O.D over each interval.
Strengths: completely insensitive to electromagnetic interference, well suited to the field, robust against water and harsh weather, simple installation and low cost consumables. Limits: one V.O.D value per interval rather than a continuous profile, with a spatial resolution that depends on the number of fibers used.
This is the method used by the all Explomet and Detomet Series, with a timing precision of 0.01 microsecond.
Continuous resistive probes
A resistive wire or coaxial probe is placed inside or alongside the explosive column. As the detonation front advances, the probe is progressively short circuited, returning a resistance versus time curve. Differentiating that curve yields a continuous V.O.D profile along the charge.
Strengths: a continuous profile and a very high spatial resolution. Limits: sensitivity to electromagnetic noise from electric detonators and nearby radio sources, a more demanding setup and a higher consumable cost per shot.
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Choosing a method
For routine V.O.D. verification in production, monitoring of blast holes in mines and quarries, and most field tests, point-by-point fibre-optic methods offer the best balance between accuracy, robustness and operating costs.
Continuous resistive probes complement them when a full V.O.D profile is required in a controlled laboratory context. Photon Doppler Velocimetry remains the reference for detonation physics research.