Inter-instrument agreement on calibrated HunterLab achromatic tiles

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FAQ: "We recently purchased and received a set of gray tiles for the LabScan XE. They are 20%, 40%, and 60% white and are calibrated. What tolerance would you recommend that we use for these tiles. If the instruments (we have four of them) read any one of the tiles out of the recommended tolerance, what should be the course of action?"

As a caveat HunterLab does not validate instrument performance on the 20%, 40% gray, and 60% while tiles your company purchased. The tolerance is for you to establish but we can offer some advice here.

The Hunter OQ Operational Qualification for your LabScan XE are the two built-in diagnostic tests in EasyMatch QC. Go to Sensor/Diagnostics for the following diagnostic tests.

  • Short Term Repeatability on White Tile to verify the electronics are in good health.
  • Long Term Repeatability on the Green Tile to verify the photometric and wavelength performance of the entire optical path is the same as when last at factory.

A PASS on both diagnostic tests affirms the instrument is operationally qualified as being in good working order. This is the basis for all HunterLab LabScan XE performance verification.

The 20%, 40%, and 60% ratings for these achromatic tiles are nominal values referring to the overall reflectance. As a further step, your company had these tiles calibrated in X, Y, Z D65/10 values specific to the tiles and LabScan XE model population. You should have the expectation that all LSXEs would read these calibrated tiles in close agreement with the assigned values.

If you baseline your 4 LabScan XEs (each operationally qualified with a PASS on diagnostic tests) on each of these tiles, this would define the degree of inter-instrument agreement you can expect to see going forward.

Our published inter-instrument agreement for LabScan XE is dE* < 0.15 as an Average; dE* < 0.36 as a Maximum and I would expect the agreement for your 4 LSXEs to be within that.

More important is that I would expect that each of your 4 LSXEs would be < 0.3 on X, Y, Z D65/10 (typically < 0.15 similar to the Green Tile) from their baseline values over time.

In terms of action if any instrument fails the inter-instrument agreement or long term repeatability to baseline of these achromatic tiles, the first step is to clean all tiles - instrument and diagnostic tiles standards along with this achromatic tile set. If you can see a fingerprint on the tile surface, our instruments can as well.

Re-standardize and re-run the achromatic 20%, 40%, and 60% tiles and see if all are within tolerance. If not, run the built-in diagnostic tests and see if the instruments is PASS on performance. Contact HunterLab if not passing.

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