MicroTrap™ Operations Manual - Edition 4.4
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7. 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 Probe Resistance with a digital Blaster’s
Galvanometer to ensure that no damage has occurred to the PROBECABLE. Damage is unlikely, as the PROBECABLE is well protected
with PVC coating.
8. At the top of the last hole, 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 conductor do not touch
each other across the connection.
9. Place the MicroTrap™ VOD/Data Recorder in a protective 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 records the data automatically.
10. Run the coaxial cable from the PROBECABLE to the MicroTrap™ VOD/Data Recorder. If necessary, shorter lengths of coaxial cable
may be connected together using the wire cutters and electrical tape to make a longer length of coaxial cable. 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™ with the blast.
Alternatively, leave sufficient slack in the coaxial cable to allow for ground movement.
11. A male BNC connector should be attached to the end of the coaxial cable that connects to the VOD input on 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 convenient
BNC Adapter has been supplied with the MicroTrap™ VOD/Data Recorder for the purpose of connecting to the MicroTrap™ VOD/
Data Recorder VOD input. A BNC Adapter is a short length of coaxial cable with a male BNC connector attached to one end, and
two bare leads on the other. 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.
12. Connect the coaxial cable to the VOD input on the back of the MicroTrap™ VOD/Data Recorder.
13. The PROBECABLE installation aspects of the test are now complete. The MicroTrap™ VOD/Data Recorder is now ready to be
prepared to record the test as detailed in Chapter 4.6.
4.5 ProbeCable And Coaxial Cable Protection
It is important to protect the PROBECABLE and the coaxial cable from damage caused by personnel and machinery operating on the
blast. It is also important to protect the PROBECABLE from damage caused by detonation of other holes and/or surface accessories such
as detonating cord, detonating relays, and shock tube bunch blocks.
The cables may be protected in many ways. Experience has shown that it is best to lead the PROBECABLE and coaxial cable under the
detonating cord and leave a barrier of sand or drill cuttings between the cables and the detonating cord. A danger point is the collar
area of the holes as the detonating cord or shock tube bunch blocks that initiate the downlines may cross directly over the PROBECABLE
or coaxial cable. A good procedure is to protect the area where there is a cross over for about 1.5 m (5 ft) along the length of cable.
Experience has shown that a sand or stemming barrier thickness of 15-30 cm (0.5-1 ft) is sufficient to protect the cables.
IMPORTANT
When shipped from MREL, the MicroTrap™ VOD/Data Recorders recording parameters have been pre-set to settings
appropriate for most blasthole VOD recording situations. Recording Rate = 2 MHz. Total Recording Time = 2 seconds,
with standard memory and 4 seconds with the MicroTrap™ VOD/Data Recorders Memory Upgrade installed. Memory
Allocation = 1 test fills the MicroTrap™ VOD/Data Recorders internal memory. Pre-trigger Time = 25% of Total
Recording Time = 0.5 seconds. Trigger Level = 95%. These settings recommendations are based on MREL’s extensive
worldwide experience in VOD recording.
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