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4.3 Using ProbeRods for Testing Samples Of Explosives
The equipment and supplies that are required to conduct VOD tests on samples of explosives or on explosive cartridges are:
• The MicroTrap™ VOD/Data Recorder System.
• VOD PROBEROD (available from MREL) - one (1) per explosive sample.
• Coaxial cable (type RG-58 is recommended) - sufficient length to run between the MicroTrap™ VOD/Data Recorder location and the
explosives.
• Wire cutters and electrical tape.
• Explosives, detonators and shot exploder.
The procedure for preparing a VOD test is as follows:
1. Demarcate the charge detonation area.
2. Place the MicroTrap™ VOD/Data Recorder in a protective shelter and/or a safe distance away from the detonation area. This distance
may be closer than what is considered safe for the User. Once the setup is completed, the MicroTrap™ VOD/Data Recorder does not
require the User to collect the data; it does so automatically without assistance.
3. Run a length of coaxial cable from the MicroTrap™ VOD/Data Recorder to the detonation area with enough excess length to
compensate for cable movement produced by the products of detonation. A male BNC connector should be attached to the end of
the coaxial cable that is to be attached to the VOD input at the back of the MicroTrap™ VOD/Data Recorder. If your reel of RG-58
coaxial cable is not equipped with a BNC male connector. A BNC Adapter has been supplied with the MicroTrap™ for the purpose
of connecting to the VOD input. The BNC Adaptor can be connected to the coaxial cable using wire cutters and electrical tape. The
connection should be “shielding to shielding” and “center to center”. Ensure that the center conductor and the shielding conductor do
not touch each other across the connection.
4. Note the Unit Resistance of the probe by reading the value in ohm/m or ohm/ft from the MREL factory label on the PROBEROD. Note
the ohm/m value if the VOD is to be reported in m/s. Note the ohm/ft value if the VOD is to be reported in ft/sec. The Unit Resistance
information will be requested later by the DAS™ Data Acquisition Suite Software.
5. Insert a PROBEROD axially in the sample of explosives. Start at the opposite end from where the detonator will be placed as shown. If
bulk explosives are being tested in a tube that has been sealed at both ends, make a small hole in the centre of each end to allow the
PROBEROD to pass through. The PROBEROD should be inserted
all the way to the orange junction where the PROBEROD meets
the two lead wires. This will ensure that the MicroTrap™ VOD/
Data Recorder triggers most dependably.
If a measurement of run-up to detonation is required, ensure
that the PROBEROD is pushed well into the explosives so
that it reaches the position of the detonator or booster. If the
PROBEROD reaches the booster or protrudes past it, the effect
of the booster will be recorded by the MicroTrap™ VOD/Data
Recorder. The same holds true for cartridges of explosives.
To test the VOD of detonation cord, tape the detonation cord
along the entire length of the PROBEROD.
6. Connect the PROBEROD to the coaxial cable using the wire
cutters and electrical tape. The polarity of the connection is not important. For the cleanest possible data, there are some items that
can help. Connect the shielding wire of the coax to the copper tube wire. This can be found easily by using a galvanometer to
measure the resistance between the lead wire and the copper tube. The lead wire with the resistance that is near zero will connected
to the shielding of the coax. Also, align the explosive sample with the coax to allow a straight line back to the recorder.
(continued on page 25.)
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