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3.7.2 VOD PROBECABLE
Two types of flexible resistance wire are available from MREL:
VOD PROBECABLE “GREEN” and VOD PROBECABLE-LR “BLUE”. These cables
have been specially developed and refined by MREL with extensive feedback and
assistance from MREL’s Blasting Instrumentation Customers since 1987. They are ideally
suited to all explosive types loaded into all blasthole conditions, including wet holes.
They have the classical configuration of a standard RG-type coaxial cable, where the
high resistance wire is the central conductor and the braided shield acts as the return
lead. A dielectric material placed between the resistance wire and the return lead
provides both electrical insulation and a physical barrier between them. This reduces
the possibility of short circuits during handling of the PROBECABLE. A PVC outer layer
protects the PROBECABLE from tearing and damage during loading of the blasthole.
PROBECABLE and PROBECABLE-LR are used for measuring VODs of explosives in blastholes as well as the delay times between holes and
decks. The selection of either PROBECABLE or PROBECABLE-LR is based on the total resistance of the circuit, which in turn depends on the
number of holes being monitored. The only difference between these two cables relates to their nominal resistance, or resistance per unit
length. PROBECABLE (GREEN) has a unit resistance of 10.8 ohm/m (3.29 ohm/ft) while PROBECABLE-LR (BLUE) (LR stands for
Low-Resistance) has a unit resistance of 3.38 ohm/m (1.03 ohm/ft). The latter allows VOD recording for lengths up to approximately
900 m (2,950 ft.) per test with the MicroTrap™ VOD/Data Recorder. Each box has a specific Quality Control Sticker that will display the
correct value to select in the DAS™ Data Acquisition Suite Software during downloading.
Both types of PROBECABLE are available directly from MREL in a unique “reel-in-a-box” packaging with 1,000 m per box. The
reel-in-a-box allows free spooling of the PROBECABLE into the blasthole by one operator without the need for a cable reel stand or
another person to hold the reel of cable. The reel-in-a-box assembly is also conveniently wrapped in waterproof plastic to prevent
degradation of the box in wet conditions. Please contact MREL for additional PROBECABLE information.
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