How to use IPG laser power meter
1. Power measurement principle
The laser probe is an absorber coated with thermoelectric material. The thermoelectric material absorbs most of the light energy and converts it into heat, and only a small part of it reflects. The ratio of absorption to reflection is related to the spectral response curve of the material. The heat storage body of the absorber and its thickness determine the speed of heat transfer to the probe and the reaction time. The temperature change of the probe can generate a current, which is converted into a voltage signal through the sheet ring resistance and transmitted.
When the laser is incident, the measured voltage rises rapidly with time, then slowly decays, and returns to zero after a period of time. This is the measured thermal phenomenon, and the rise and decay times are not affected by the load resistance.
The difference between the maximum voltage and the initial voltage is the measured voltage, and the measurement accuracy is authorized by NIST. As long as the maximum energy is not overloaded, the measurement accuracy can be guaranteed.
The actual picture of a thermocouple is a structure with different metals attached to both ends, one end is the “hot end” and the other end is the “cold end” or reference end. During laser measurement, the hot end absorbs laser energy and the other end sinks. Any temperature change at both ends will generate a voltage between the two ends. This is the data measured by the power meter.
2. Calibration of power meter
The purpose of power meter calibration is to calibrate its own measurement accuracy to ensure that the measured value is within the error range of the power meter usage report, so as to ensure the normal use accuracy of the power meter.
The calibration of the power meter is measured by a third-party power meter. According to the factory calibration report, different powers are used to verify the accuracy and stability of the actual calibration of the power meter without damaging the power meter.
Power calibration is usually required every 12 months.
Power measurement is a process of obtaining the true value of power based on system and random errors, and there is a certain power uncertainty. For power measurement, there are two types of power, one is accuracy, that is, the deviation between the measured value and the true value; the other is power stability, that is, the range of power fluctuations measured repeatedly under the same condition.
3. How to use the power meter
To use the power meter for the first time, a measurement standard needs to be established, and subsequent measurements are carried out on the basis of this standard to ensure the consistency of the measurement.
Usually the power meter is fixed on a horizontal workbench. During measurement, the robot moves the laser head to the measuring point to ensure that the guiding light is basically aligned with the light receiving surface (circular surface) of the power meter, and the deviation is within 2mm.
The measurement standards include: the center of the light spot and the light receiving surface of the power meter
(1), the ratio of the light spot to the light receiving area of the power meter (2), the distance between the lower end of the laser head blowing module and the upper surface of the power meter
(3), and the measurement of the light time
( 4), measure the optical power
(5) and other parameters.
For the first measurement, write the standard measurement program and robot motion trajectory, teach the running path, and accurately control the light position and posture of the robot. The final measurement point needs to be reached accurately. In order to prevent the position of the measurement point from moving and difficult to retrieve, it is necessary to use the final measurement point posture as the reference, and translate about 10mm upward as the error prevention point of the measurement point. It also needs to be accurately reached.
Before measurement, ensure that there is no interference from welding wire, dirt, oil, water and other foreign objects in the measurement optical path! Protect the lens clean and meet the measurement requirements. At the same time, remove the protective cover!
The minimum power measurement interval time is 1min, and the maximum measurement energy is 200J. If 4kW is used, the maximum measurement time does not exceed 50ms, and if 3kW is used, the maximum measurement time does not exceed 66ms. The recommended measurement time is 40ms.
For subsequent use, only one type of power (such as 3kW) is needed to judge the stability of the power. If the stability exceeds ±5%, remove the measurement error and perform the measurement again, consider replacing the protective lens or checking the cleanliness and integrity of the power meter receiver.
The same power and the same light emission time have been measured many times, and the power stability exceeds ±5%. Under the premise that the power meter is not damaged, it is necessary to check the cleanliness of the optical path inside the laser head (this operation must be performed by the laser head manufacturer or a person authorized by the laser head manufacturer get on).
If the power meter is damaged during use or improper use and operation results in excessive measurement errors, consider recalibrating the power meter.
4. Maintenance and maintenance of power meter
The power meter is a precision instrument and needs to be carried out in strict accordance with the use requirements to ensure the accuracy and stability of the measurement.
The best temperature for use is around room temperature (25°C). Make sure to operate in an impossible environment during use;
The energy range used is 50~75% of the maximum energy, and the measurement spot size is 40~80% of the effective measurement size.
When using for the first time, you need to measure the power value corresponding to 0 input for calibration;
The recommended measurement gap time is 3min;