Recovering from a bad zero or span; how to undo your doings.

Recovering from a bad zero or span; how to undo your doings.

The LI-7700 is an inherently stable laser-based analyzer that requires minimal user calibration during normal use. User calibrations can still be performed to validate instrument performance, and are required when changing the instrument from its warm to cold temperature operating range. The possibility does exist, however, to perform an incorrect user calibration, which will have undesirable effects on instrument performance.  The instrument software provides multiple ways to help prevent, and even undo, a bad user calibration to ensure high quality data. In this TechTip we detail four simple ways to undo what’s been done when a zero or span calibration goes awry.

1.     Are you sure you want to do this? When setting a zero or span from the Windows interface software, users are given the option of “aborting” or “committing” a zero or span after initiating it.

2.     Back to basics: A factory reset button is present in the Calibration menu that resets the instrument to a non-zero, non-spanned state. While this isn’t the state the instrument actually left the factory in, (as all instruments are shipped with verified zero and span), it will bring instrument response back to a reasonable range and provide users a good starting point for resetting things.

3.     It’s ancient history: All zero and span settings are stored in on-board memory on the LI-7700 and can be accessed through the instrument’s Finder application. On the Cal page, individual settings can be reset to a previous state using the “Rollback” button.

4.     If all else fails, there is always the manual way. From the Cal page in the Finder application, the Advanced button allows users to manually enter the zero and span offsets they want to use. The factory offsets can be found on the calibration sheet shipped with the instrument, or user-defined offsets can be found in the on-board calibration history.

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