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Monday, January 11, 2016

Opacity Calibration: What is the value of paper calibration versus the opal standards?

This time of the year most customers have renewed their paper calibration subscriptions for the next 12 months. Others forgot to renew and start to wonder, do I really need paper calibration standards since I have opal glass standards?

During primary calibration the paper calibration standard is used to adjust the white body for proper calibration. The opal glass is a different material and that difference is important for verifying translucency.  This allows for confirming calibration and verification of  opacity from paper to opal and back. In other words, this process is used to make sure the opal glass is a valid way of doing day to day calibrations since the tile is mineral and the end use product is paper (or flexible packaging). Lamp position, chromatic output, focus, and so forth all affect the relationship between paper and the tile. The biggest single item is the chromatic output (amount of light and spectral response).  The lamp age and position are the critical factors related to the chromatic output of the lamp. The paper standard is required for full primary calibration and should be done monthly regardless of how often or when Preventative Maintenance is performed.

The question to ask is, "how critical is the accuracy of your day to day measurements?" If a paper calibration is performed, and this if followed by measurement with opal glass, the opal glass will keep the calibration close even if monthly, paper primary calibrations are not performed. However, if a lamp is changed or if there is a noticeable shift in performance then primary calibration to the paper standard is vital to ensuring accuracy when measuring paper products (or flexible packaging). Paper standards degrade with time. That’s why paper standards are only certified for 6 weeks from the issue date when unopened, or 3 weeks after opening. A quarterly subscription will keep you close, but a monthly subscription will keep you fully TAPPI T 425 compliant.

Forward any of you calibration question or concerns.

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