Primes PROFINET - Measurement with Pulsed Lasers (Only PMM Type Ap3 S)

PowerMeasuringModule PMM
35,0(
6
42
Revision 13 EN - 02/2023
8.7 Measurement with pulsed lasers (only PMM type AP3s)
When measuring pulsed lasers, the technical specification according to chapter17 „Technical data“ on
page88 must be observed.
When using pulsed laser radiation a correct irradiation time measurement up to a pulse frequency of 10kHz
and a duty cycle of 50% is possible. In case of ontimes/offtimes shorter than 50μs a correct irradiation time
measurement is not possible.
Measurements outside the specification may result in an incorrect calculation of the number of pulses. This
affects the calculated average power. But not on the measured energy.
When measuring pulsed lasers, as of firmware version3.2, the power (measured power) is calcula-
ted with a corrected burst duration (see Fig. 8.6 on page42).
For devices with former firmware versions, the power (measured power) is calculated with the un-
corrected burst duration. This leads to an increased value of the average power.
With pulsed lasers, the device detects the number of pulsesn and the number of pulse pausesn-1 (the last
pulse pauset
off
is not measured, for physical reasons).
The burst duration here is (t
on
+t
off
)∙n-t
off
. This leads to a significantly increased value of the power (measu-
red power) for a low number of pulses.
The power is therefore calculated for devices with firmware version3.2 and higher on the basis of a correc-
ted burst duration: (t
on
+t
off
)∙n (see Fig. 8.6 on page42).
t
on
t
off
t
off
Uncorrected burst duration
Corrected burst duration for the calculation of the average laser power
Laser power P in W
Time t
Pulse 1 Pulse 2 Pulse 3
Pulse 4
Pulse 5
Fig. 8.6: Uncorrected and corrected burst duration with pulsed lasers
The deviation of the laser power is the ratio of corrected to uncorrected burst duration:
Deviation =
(t
on
+ t
off
) ∙ n
(t
on
+ t
off
) ∙ n - t
off
The values for t
on
and t
off
illustrated in Fig. 8.6 do not correspond to the values for „Ontime“ and „Offtime“ in
the registry settings: Ontime=t
on
∙n and Offtime=t
off
∙(n-1).
For cw lasers respectively one pulse, the average power corresponds to the maximum power of one pulse.