MicroTrap™ Operations Manual - Edition 4.4
34
If the number of tests selected is one, the available recording time will be maximized for a given Recording Rate.
For example, at the maximum Recording Rate 2 MHz, the Total Recording Time will be:
4,194,000 points / ((1 test) x (2,000,000 points/sec)) = 2.097 seconds
At a slower Recording Rate of 1 MHz (for example), the Total Recording Time will become 4.194 seconds. If the MicroTrap™ VOD/Data
Recorders internal memory is divided into 4 tests, the MicroTrap™ VOD/Data Recorder will partition the memory allocating 4,194,000
points/4 tests = 1,048,500 points per test.
Following the previous example, the Total Recording Time per test can be calculated as follows:
4,194,000 points / ((4 tests)x(2,000,000 points/sec)) = 0.524 seconds per Test
If the Recording Rate is reduced to 1 MHz, the Total Recording Time will become 1.048 seconds per test. If these recording times are
insufficient for your testing applications, then contact MREL and ask about the MicroTrap™ VOD/Data Recorder Memory Upgrade, which
doubles the MicroTrap™’s internal memory and thus doubles the Total Recording Time.
4.9.2 Triggering
When the EXT/INT switch is set to the EXT position, the trigger signal that the MicroTrap™ VOD/Data Recorder receives is from the Trigger
Wire as detailed in Section 4.8. This corresponds to time = 0 on the resulting VOD graph.
When the EXT/INT switch is set to the INT position, then the MicroTrap™ VOD/Data Recorder is triggered 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 MicroTrap™ VOD/Data Recorder. When the voltage across the probe reaches
the value corresponding to the Trigger Level selected by DAS™ Data Acquisition Suite Software, the MicroTrap™ VOD/Data Recorder is
triggered. This represents time = 0 on the resulting VOD graph. For example, with a Trigger Level setting of 95%, the MicroTrap™ VOD/
Data 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 MicroTrap™ VOD/Data 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 DAS™ Data
Acquisition Suite 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 MicroTrap™ VOD/Data
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 MicroTrap™ VOD/Data Recorder (3,000
ohms).
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