OPHIR vega User Manual page 52

measurements of pulses below about 4 times the
threshold level. The factory setting of energy threshold is
"Med" for medium. If the unit triggers on noise, set the
threshold to "High." If you are measuring small energies
and the unit does not trigger, set the threshold to "Low."
To set the energy threshold:
1. From the
"Threshold ".
2. Select "High," "Medium," or "Low" threshold. For some
3A-P models, "Optical" is also available and is the
default choice (See below).
3. Enter again to return to main measurement screen. If
you wish to save this value, press "Save" before
exiting. (See also section 4.3).
4.5.4. Measuring Pulses of Very Low Energy
When it is necessary to measure pulses of very low
energy, i.e., less than 0.5% of the maximum range of the
instrument, the following two alternative methods allow
greater accuracy to be obtained.
1. A continuous train of pulses may be fired, and the
average power measured using "Power" mode. The
energy per pulse can be calculated by:
Average Energy per pulse = Average power /
Pulse Repetition Rate
2. A train of a known number of pulses may be fired, and
the total energy measured in "Energy" mode. This
train should not exceed 5 seconds duration. The
energy per pulse can be calculated by:Average
Energy per pulse = Total Energy / Number of Pulses
In both of the above methods, the pulse repetition rate
must exceed 3Hz.
improved accuracy, but care should be taken not to
exceed maximum power ratings.
energy measurement
Higher rates will generally give
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screen, enter