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BNC Adapter has been supplied with the MicroTrap™ VOD/
Data Recorder for the purpose of connecting to the
MicroTrap™ VOD input. The 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. It is a good practice to check
the total resistance of the PROBECABLE and coaxial cable.
Ensure that the total resistance is between 50 and 3000
ohms.
10. Connect the coaxial cable to the VOD input located on the back of the
MicroTrap™ VOD/Data Recorder.
11. The PROBECABLE installation is complete. The MicroTrap™ VOD/Data
Recorder is now ready to be prepared to record the test as detailed in
Chapter 4.6.
4.4.2 Preparation of ProbeCable for Multiple
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. Start at the first blasthole in the sequence, attach the short circuit end of the PROBECABLE to the booster or to a rock using tape or
wire, and lower the PROBECABLE into the hole. Detonation cord downlines may damage the PROBECABLE or cause side initiation of
the bulk explosive, therefore when using detonation cord you should attach the PROBECABLE to a rock and lower it on the opposite
side of the blasthole from the detonation cord downline.
3. Run the PROBECABLE between the first hole and the second hole leaving sufficient slack between the holes to allow for ground
movement between the delayed holes. Coil the slack cable near the collar of the second hole.
4. Each blasthole following the first hole will require a doubled length of PROBECABLE in order to form a continuous circuit throughout
the blast. There are two common methods of lowering a doubled length of PROBECABLE in these holes. The first and simplest method
is to run the PROBECABLE through a wire loop that has been tied or taped around a rock or booster. This allows the rock to slide
along the PROBECABLE as the PROBECABLE is lowered into the hole, until the rock reaches the bottom of the hole. The second method
is to measure out the midpoint of the length of PROBECABLE that is to be lowered into the hole, and attach the rock or booster so that
it reaches the exactly the bottom of the hole when inserted.
5. After the last hole to be recorded has been loaded with PROBECABLE, the PROBECABLE can then be cut a short distance from top of
that hole.
6. Note the Unit Resistance of the probe by reading the value in ohm/m or ohm/ft from the MREL factory label on the box 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 its length). If this is not the case then remove the length of PROBECABLE and reload another length into the
hole.
Figure 3
This tape marks
1m (39 in.) from
the end of the
PROBECABLE.
NOTE: If the out-of-range Low light is on, there is probably a
short or less than 4 m of PROBECABLE. If the out-of-range
High light is on, there is probably an open circuit somewhere.
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