The concept behind measurement assurance is to establish an in tolerance condition at the beginning of each measurement session. This is best accomplished by taking a scrap part with coating thicknesses similar to what will be measured on a regular basis and using it as a check standard. Calibrate the XRF instrument with traceable calibration standards in accordance with the manufacturer's operating and safety instructions.

Measure each calibration standard to verify the performance of the calibration. When it is determined that the instrument is measuring within tolerance, mark a spot on the part by drawing a small circle where you would normally measure. Measure 25 times. within the marked spot. Mark the part with the average of the 25 measurements. Determine a reasonable allowable tolerance on this area by examining the standard deviation of the measurements and considering the need for performance and production.

Measure this check standard at the beginning of each measurement session at least 7 times. Remember that XRF measurement should be considered a process. Therefore it is important to examine groups of measurements to quantify instrument performance. When a group size n<=6, the range of the measurements in this set is an appropriate indication of the range of measurements the instrument is producing. When a group size n=>7, the standard deviation of the measurements in this set is an appropriate indication of the range of measurements the instrument is producing. Record the mean and standard deviation of this set of measurements and compare with your allowable tolerance.

If this mean falls within tolerance, proceed with your measurement session. Otherwise, proceed with the appropriate steps to correct your instrument, including referencing and normalization. Repeat the set of measurements and record the data. If the mean still falls outside the tolerance, recalibrate and repeat the verification measurements on the calibration standards.

Abstract
Accuracy and Precision
Principle of Measurement
Gold and Nickel Measurements on Copper
Gold and Nickel Measurements on Phosphor Bronze
Gold and Nickel Measurements on Kovar and Other Glass-Sealing Alloys
Gold and Nickel Measurements on FR-4 Circuit Board Substrates
Tin-Lead Solder on Copper, FR-4 Circuit Board Substrates, and Kovar
Tin-Lead Solder on Phosphor Bronze
Adjustments for Part Geometry
Measurement Assurance
Conclusion