Measurement system analysis with XRF spectrometers

Precision and optimization in practice.

In industrial manufacturing, product quality depends crucially on the production equipment and measurement methods used. Regular quality checks ensure the stability of manufacturing processes. However, the results of these checks are only reliable if the underlying measurement processes are precise and robust. Measurement system analysis (MSA) is a proven tool and strategic basis for testing the suitability of a measurement process while identifying optimization and cost potential.

Objectives and influencing factors of measurement system analysis.

The primary objective of MSA is to clearly assess whether a measurement process is suitable for the respective measurement task. In addition, the analysis provides information about which factors influence measurement accuracy. These can be divided into seven categories: human, environment, measurement object, measurement method, measuring equipment, recording device, and evaluation method. The user is therefore just as much a part of the measurement process as the measuring device or external environmental conditions.

Before an MSA is performed, the resolution of the measuring equipment must be checked. Only with sufficient resolution can the required measured values be reliably read and precisely determined.

MSA procedure with X-ray fluorescence spectrometers.

When analyzing with an X-ray fluorescence (XRF) spectrometer, the MSA is divided into several procedures:

Method 1 checks the basic applicability of the measurement process. The focus here is on accuracy and repeatability. A standard (reference material) with a known characteristic value is measured several times, typically 50 times The standard deviation and the systematic measurement deviation are determined from the measurement results. Based on this, the potential capability index Cg and the critical capability index Cgk can be calculated. While Cg considers the dispersion, Cgk also takes systematic deviations into account.
Methods 2 and 3 specifically incorporate external influences such as humans, the object being measured, the environment, and the recording device in order to test the measurement process under real conditions. High-quality XRF devices minimize these influences through automation, for example with a programmable XY sample table, autofocus, and object recognition.

Optimization of the measurement process.

If the dispersion of the measurement results is too high, the simplest approach is to increase the measurement time, as this reduces the standard deviation. Further optimization options are available by adjusting the counting rate using larger collimators, capillary optics, X-ray tubes, filters, or detectors. However, the dead time of the detector must be taken into account: if the count rate is too high, photons will no longer be registered. Modern devices from FISCHER , however, can process very high count rates and handle all common measurement tasks with ease.

If the Cg value meets the requirements but the Cgk value does not, this indicates systematic measurement deviations. Causes can include insufficient calibration, inaccurate recording devices, human influences, or the inhomogeneity of the standards. During calibration, it is important to use the same standard as for the subsequent measurement in order to check the measuring device itself. Inhomogeneities can occur with certain material systems or customer-specific standards. In such cases, the mean value is determined over several measuring points within the certified area, which is facilitated by automated XY tables or scan modes.

_{Figure 1. Increasing the measurement time is the simplest measure to improve the dispersion in XRF. In this example, the measurement was performed on 0.1 μm gold layers.}

Conclusion

Measurement system analysis is an indispensable tool for ensuring and optimizing the reliability of measurement processes. Through the targeted investigation of dispersion, systematic deviation, and influencing factors, measurement processes can be improved, measurement times reduced, and measurement costs lowered. High-quality XRF devices from FISCHER help users minimize external influences and achieve precise, reproducible measurement results. This is a decisive factor for consistent product quality in manufacturing.

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