Thermopile Sensors
1919-R User Manual
34
It would then fail to measure the intended pulse. Since there is always some degree of noise
or background radiation, the instrument is designed not to respond to pulses below some
preset minimum size. This "Minimum Energy Threshold" is typically set to 0.3% of full scale of
the selected range. If this level is found to be too sensitive for the user's particular
environment, it may be altered by the user. The threshold should not, however, be raised
higher than necessary. This will cause a degradation in the accuracy of energy measurements
of pulses below about 4 times the threshold level.
5.
When the 1919-R screen flashes
READY
on and off, fire the laser. The display will go blank
while the energy is being integrated. After about 2-4 seconds (depending on the sensor), the
correct energy will be displayed.
6.
Return to Step 1 for the next measurement.
shows a sample analog Needle display showing laser energy measurement
data with options for
. (Click the above links for more details.)
Figure
5-3 Thermopile Energy in Needle Display
Note:
The soft key legend options such as
Zoom
,
Offset
,
Persist
,
Reset
vary per
Graph Type
.
5.3.1
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.
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
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. Higher rates will
generally give improved accuracy, but care should be taken not to exceed maximum power
ratings.
