Check measurements of magnetic flux density: Equipment design and the determination of the confidence interval for EFA 300 measuring devices

The stability of the measuring device is associated with its accuracy at repeated measurements provided under the same conditions. We designed equipment for checking of the measurement accuracy and stability of the device EFA 300 that we called Stability Control Stand (SCS). The reason for our interest in the development and realization of the SCS was based on the internal need for laboratory checks of device EFA 300. The magnetic flux density B at different distances from the probes to the electromagnetic field source in the anechoic chamber was measured. In the experiment, we used the method of repeated measurements. The distribution of magnetic field has been verified through mathematical simulations. The measured values of the magnetic flux density are almost identical to the values which are simulated using the mathematical model. With respect to the sensitivity and accuracy, we identified the optimal distance of 20 cm from the source of magnetic field to the geometric center of the probe in which the probe indicates the most accurate values. The measured data were processed using a mathematical statistics and subsequently, the expanded measurement uncertainty and confidence interval was calculated. The processed results with the expanded measurement uncertainty represent the B like reliable values at the next measurements with SCS.