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7. Connect the coaxial cable to the VOD connector located on the back of the MicroTrap™ VOD/Data Recorder, as shown to the right.
8. The PROBEROD installation aspects of the test are complete. The User can now place the detonator and connect it to the shot
exploder as per standard procedures. The MicroTrap™ VOD/Data Recorder is now ready to be prepared to record the test as
detailed in Chapter 4.6.
4.4 Using ProbeCable for Testing Explosives In Blastholes
The equipment and supplies that are required to conduct VOD tests on samples of explosives in blastholes are:
• The MicroTrap™ VOD/Data Recorder System.
• VOD PROBECABLE “GREEN” or VOD PROBECABLE-LR “BLUE” (available from MREL).
• Coaxial cable (type RG-58 is recommended) - sufficient length to run between the MicroTrap™ VOD/Data Recorder location and the
last blasthole in the blast to be recorded.
• Wire cutters and electrical tape.
• Explosives, detonators and shot exploder.
4.4.1 Preparation of ProbeCable for Single Blasthole Recording
1. Prepare the end of the PROBECABLE by using the wire cutters to remove the insulation from the end. Then short the PROBECABLE by
connecting the shielding wire to the center conductor wire and twist them together. Protect the connection well with electrical tape.
2. Using tape or wire, attach the short circuit end of the PROBECABLE to the primer/booster or to a rock and lower the PROBECABLE
into the hole as shown in the diagram on the following page. Detonation cord downlines may damage the PROBECABLE or cause
side initiation of the bulk explosive. When initiating with detonation cord, attach the PROBECABLE to a rock and lower it on the side
of the hole opposite to the detonation cord downline.
3. The PROBECABLE can then be cut at the top of the hole.
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 spool of
PROBECABLE. 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. When measured with
a blaster’s galvanometer, the Probe Resistance should compare closely with the calculated resistance of the PROBECABLE (Unit
Resistance multiplied by length). If this is not the case then remove the length of PROBECABLE and reload another length into the
hole.
5. The hole can now be loaded with explosives and stemming per usual procedure. Hold the PROBECABLE taut during the loading of
the explosive to avoid slack in the hole. If you will not be present during loading, tie the PROBECABLE taut around a hole marker
stake, or around a rock at the top of the borehole. After loading, you may wish to check the total resistance of the PROBECABLE to
ensure that no damage has occurred. Damage is unlikely, as the PROBECABLE is well protected with PVC coating.
6. Connect the PROBECABLE to the coaxial cable using the wire cutters and electrical tape. The connection should be “shielding to
shielding” and “center to center”. Ensure that the center conductor and the shielding connections do not touch each other.
7. Place the MicroTrap™ VOD/Data Recorder in a protective shelter (a short piece of steel pipe is a good shelter) and/or a safe
distance away from the blast area as dictated by flyrock. This distance may be closer than what is considered safe for the User.
When set, the MicroTrap™ VOD/Data Recorder does not require a User to collect the data; it will record the data automatically.
8. Run the coaxial cable from the PROBECABLE to the MicroTrap™ VOD/Data Recorder. Shorter lengths of coaxial cable may be
connected together using the wire cutters and electrical tape. Somewhere along the length of the coaxial cable, loop the coaxial
cable around a large rock. When the blast is fired, and the ground moves, looping the coaxial cable around a large rock will stop
the blast from pulling the coaxial cable, and the MicroTrap™ VOD/Data Recorder, with the blast. Alternatively, leave sufficient slack
in the coaxial cable to allow for ground movement.
9. A male BNC connector should be attached to the end of the coaxial cable that is to be attached to the VOD input on the
MicroTrap™ VOD/Data Recorder. If your reel of RG-58 coaxial cable is not equipped with a BNC male connector, a convenient
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