Primes PROFINET - Waiting Times until the Next Measurement in Repepetive Measurements; Calculation of the Irradiation Time

PowerMeasuringModule PMM
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Revision 13 EN - 02/2023
8.5 Waiting times until the next measurement in repepetive measurements
With high measuring frequencies, the measuring accuracy can be limited. For repetitive measurements within
the specified accuracy, the following waiting times prior to the next measurement are recommended.
Energy input in J Waiting time in s
200 50
400 100
600 150
800 200
1000 250
Tab. 8.3: Waiting time until the next measurement in repepetive measurements
8.6 Calculation of the irradiation time
The selection of a certain irradiation time is based on three different criteria:
1. The minimum irradiated energy should amount to at least 10% of the total capacity of the absorber (Vari-
able: “Max. Capacity”). This requirement ensures best measurement accuracy (5% may be acceptable if
the repetition rate is a priority). See also point 2.
2. In case of a repeated power measurement within a short period of time, a maximum of 50% of the re-
sidual absorber capacity of the test piece must be used. (Variable: “Remaining Capacity”)
3. The irradiated energy may not exceed the “Remaining capacity”, otherwise the absorber may be over-
heated during the measurement.
With the following formula the irradiation time can be determinated:
Δ t = Remaining capacity / Laser power
Δ t = Irradiation time
Remaining capacity = Remaining capacity after a measurement
Laser power = Total power of the laser beam
A constant irradiation time ensures a best possible performance and repeatability.
Even with absorbers at room temperature the remaining capacity does not reach the "Maximum ca-
pacity". This is due the fact that the “Maximum capacity“ refers to an absorber temperature of 0°C.
Example
• MaxCapacity = 4000 J
• Remaining capacity = 3000 J
• Minimum energy = 400 J
• Laser power = 8000 W
 selected: 100 milliseconds
The irradiation time of 100ms leads to an irradiation of 800J. This means, the minimum amount of energy
of 400J is clearly exceeded. Furthermore, this irradiation time enables two more power measurements, that
can be carried out immediately.