Thermopile Sensors
1919-R User Manual
35
5.3.2
Measuring Energy of Rapidly Repeating Pulses
With a typical Thermopile sensor, 1919-R will only measure individual pulses every 5 seconds or
so. You can also calculate the average energy of rapidly repeating pulses by measuring average
power on the power setting and using the formula:
Average Energy per Pulse = Average Power / Pulse Repetition Rate
For rapidly repeating pulses, you can use one of the Newport Pyroelectric sensors, as long as the
pulse energies do not exceed the ratings of the Pyroelectric absorbers. The Pyroelectric sensors
are compatible with 1919-R and just have to be plugged in to be used.
5.4
Measuring Laser Pulsed Power with Thermopile Sensors
Thermopile Energy Sensor models are capable of measuring “Pulsed Power” in order to display
instantaneous power of a laser pulse. Power can be calculated from energy if you know the length
of the pulse.
Note:
Accuracy of measurement will be dependent on your setting the pulse width correctly.
To measure laser pulsed power when using Thermopile sensors:
1.
Set
Mode
to
Pulsed Power
. The measuring mode is set to
Pulsed Power
, and you can specify
the expected energy
Range
,
Laser
setting, and
Threshold
.
2.
Set
Range
to the appropriate manual range. (In
Energy
mode, there is no autoranging.) The
correct range is the lowest one that is larger than the expected maximum pulse energy of the
laser.
3.
Set
Laser
to the appropriate laser setting.
4.
Set
Pulse Length
to the correct pulse length. Using the up/down Navigation keys to change
each number and the right/left keys to move to the next number, key in the pulse length you
want. (The range is
0.1
to
10
seconds in increments of 0.1. The default is 1.0 seconds.) When
finished, press the
Enter
key.
5.
Set
Threshold
to change the energy threshold to
LOW
,
MED
, or
HIGH
to set the hardware
threshold in the sensor to screen out noise that would otherwise be seen as energy pulses.
(This screens out false triggers.) The factory setting of the 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
.
If the 1919-R is used in a noisy environment or where there is a high level of background
thermal radiation, the instrument may trigger spuriously on the noise or background radiation.
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.
