Primes PROFINET - Functional Description; Measuring Principle

PowerMeasuringModule PMM
35,0(
6
14
Revision 13 EN - 02/2023
4.2 Functional description
The PMM is used to measure laser power. After opening the shutter, the laser beam hits the absorber and
scattering light is registered by a photodiode. The absorber and the photodiode are protected from contami-
nation by the protective window. The shutter and the caps on the ports protect the PMM from contamina-
tion. Thus, the PMM can be used directly in the production environment in the process zone.
The PMM operates without cooling water and compressed air. The absorber cools off only through thermal
conduction to the ambient air.
Thanks to the availability of various fieldbus interfaces, the PMM can be integrated in nearly every existing
machine. The measurement results are transferred directly to the PLC.
Laser beam
Protective window
mount
Port
Protective window
Cover caps
Shutter
Fig. 4.2: PMM with open shutter using the example of PMM PROFINET
®
4.3 Measuring principle
The PMM offers a fast, passively cooled power measurement according to the calorimetric measuring prin-
ciple. The absorber of the measuring device is briefly irradiated with the laser beam. The irradiated energy is
determined by the temperature rise of the absorber.
The photodiode simultaneously determines the laser ontime. The high-frequency sampling rate of the
photodiode enables single pulse detection for pulses not shorter than 50μs.
Thus, in addition to the average power, the peak power can also be calculated. In the second step, the ac-
tual laser power is calculated from the absorbed energy divided by the laser ontime.