MicroTrap™ Operations Manual - Edition 4.4
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NOTE: When the internal triggering criteria are met, the MicroTrap™ VOD/Data Recorder will send a 10 VDC signal to the TRIG OUT
port on the back of the unit. This pulse is 6 seconds in duration, and has a rise time of 2 microseconds. Some Users may wish to
trigger other instrumentation from the MicroTrap™ VOD/Data Recorders TRIG OUT port.
10. Once data collection ends, the TRIG’D and START lights flash rapidly and the MicroTrap™ VOD/Data Recorder begins storing data
into its non-volatile memory. During this short time, the STATUS light is illuminated to indicate that writing is taking place. Do not
switch the MicroTrap™ VOD/Data Recorder OFF during this time.
11. When the MicroTrap™ VOD/Data Recorder finishes storing the data, the START light will go dark and the STATUS and TRIG’D lights
will begin to flash slowly. The MicroTrap™ VOD/Data Recorder has now returned to Stand-by mode.
12. If no more experiments are to be conducted and the data storing process has been finished (St e p 11 above), then the data are ready
to be transferred to a computer using the DAS™ Data Acquisition Suite Software as detailed in Section 6.1. If data transfer is to be
conducted later, then the MicroTrap™ VOD/Data Recorder can be switched OFF and the data will remain in the MicroTrap™ VOD/
Data Recorder non-volatile memory.
5.5 Utilizing the External Trigger
In some data recording applications, it may be desirable to
have the MicroTrap™ VOD/Data Recorder begin to record exactly
when a specific external event occurs. For the specific event to
trigger the MicroTrap™ VOD/Data Recorder, and subsequently
correspond to time zero on the graph, the EXT TRIG port is used.
The EXT TRIG function operates on the simple concept of MAKE or
BREAK circuits. Both types of trigger capitalize on the fact that the
EXT TRIG port outputs a constant voltage after the START button is pressed. The traditional MAKE circuit is triggered when the open circuit
is closed by the event of interest, even if only momentary. The traditional BREAK circuit is triggered when the complete circuit is broken,
even if only momentarily.
To create a MAKE or BREAK trigger using the EXT TRIG port, connect a BNC Adaptor to the port and subsequently connect a “duplex”
(two wired) cable to the adaptor. A good example of a duplex wire that is fit for duty as a trigger line is the lead line used for initiating
electric detonators in the field.
An example of a MAKE trigger would be to twist the duplex wire with itself, leaving the insulation on each wire, and then run it over the
tip of a detonator or around a section of detonating cord, so that upon detonation of the explosive, the insulation is stripped and the two
wires are forced into contact with each other under pressure from the explosive. This momentary contact will complete the MAKE circuit
and thus trigger the MicroTrap™ VOD/Data Recorder. The MAKE trigger is especially dependable because the explosive itself generates
an electrically conductive plasma in the vicinity of the detonation front, that will assist in arcing the current from one wire to the other.
Ensure that the resistance of the external trigger wires have a total resistance below 100 ohms in order to detect the change in status to
trigger the unit. It is always best to test the external trigger if possible.
An example of a BREAK trigger would be to wrap a duplex wire around an object that is expected to deform or expand during the event
of interest, and then twist the bare ends of the wires together so as to complete the circuit. When this object deforms or expands, the
wires will disconnect and cause the circuit to open - triggering the MicroTrap™ VOD/Data Recorder. Beware that even a momentary break
in the trigger circuit will cause the MicroTrap™ VOD/Data Recorder to trigger. Avoid disturbing a BREAK trigger once the START button
has been pressed. Ensure that the resistance of the external trigger wires have a total resistance below 100 ohms in order to detect the
change in status to trigger the unit. It is always best to test the external trigger if possible.
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