MREL DATA TRAP II, Operation Manual

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by the signal received from the probe placed in the explosives. This trigger signal occurs according to the following principle: when the
explosive detonates, the probe is consumed and the probe length is reduced. This in turn reduces the resistance and thus the voltage
across the probe decreases from the initial 5.0 VDC (approximately) set automatically by the
DataTrap II™ Data/VOD Recorder . When the
voltage across the probe reaches the value corresponding to the Trigger Level selected by software, the DataTrap II™ Data/VOD Recorder
is triggered. This represents time = 0 on the resulting VOD graph. For example, with a Trigger Level setting of 95%, the DataTrap II™ Data/
VOD Recorder will be triggered when the voltage signal coming from the probe crosses the 95% level (4.75 VDC of the full-scale voltage,
which is approximately 5.0 VDC).
Once the DataTrap II™ Data/VOD Recorder receives the trigger signal, it stores the VOD information received immediately prior to the
trigger signal into the pre-trigger memory; the VOD information received after the trigger signal is stored into the post-trigger memory. The
recording time for each memory allocation (pre and post-trigger) will depend on the setting selected, using the software, for Pre-Trigger
%. The DAS™ Data Acquisition Suite Software automatically calculates and displays the Total Recording Time per Test and the Pre-Trigger
Time. For those Operators with additional interest in recording times:
Pre-Trigger Time = (Total Recording Time) x Pre-Trigger %
Post-Trigger Time = (Total Recording Time) - (Pre-Trigger Time)
For the PROBECABLE or PROBECABLE-LR length loaded in the blastholes, and the recommended TRIG% setting of 95.3%, the graphs on the
following pages show the lengths of PROBECABLE and PROBECABLE-LR that must be consumed for the DataTrap II™ Data/VOD Recorder
to receive the INTernal trigger signal. PROBECABLE-LR should be used for tests involving several holes where if PROBECABLE was used it
would result in the Total Resistance exceeding the maximum resistance accepted by the DataTrap II™ Data/VOD Recorder (3,000 ohms).
For example, at a 95.3% Trigger Level and with 250 metres of PROBECABLE loaded into blastholes, then 28 metres of PROBECABLE must
be consumed to trigger the DataTrap II™ Data/VOD Recorder . If the first hole does not consume a sufficient length of PROBECABLE to
trigger the DataTrap II™ Data/VOD Recorder , then all of the VOD data for the first hole will be before time = 0.
The Operator should ensure that there is sufficient Pre-Trigger time to record the time it takes for the trigger length of PROBECABLE to be
consumed in the blast. This is particularly important if several delayed holes must be detonated in order for sufficient PROBECABLE to be
consumed. The DataTrap II™ Data/VOD Recorder has a very large memory and a very long Total Recording Time. At a Pre-Trigger %
setting of 25%, the DataTrap II™ Data/VOD Recorder has a long Pre-Trigger Time . It is likely that there will always be sufficient Pre-Trigger
Time to record the time it takes for the trigger length of PROBECABLE to be consumed in the blast.
If there is insufficient Pre-Trigger time , the best procedure is for the Operator to re-program the DataTrap II™ Data/VOD Recorder using the
Software and increase the Pre-Trigger % to increase the amount of Pre-Trigger Time to suit the test. Alternatively, the Operator can reduce
the Recording Rate to increase the amount of both Pre and Post-Trigger Time.