What are the different ways the term "calibration" can be interpreted?

Document ID

Document ID TE13021

Published Date

Published Date 04/19/2022
Question
What are the different ways the term "calibration" can be interpreted?
Summary
An outline of the different contexts and definitions for the term calibration.
Answer
"Calibration" is a term that can have different meanings in different contexts. So sometimes when the term “calibration” is used, the context and meaning will need to be clarified.
 
Here are the most common contexts/meanings:

Preventative maintenance and Recertification service- The act of checking the full specifications of the instrument and documenting the tolerances and results of this check in the form of a certificate. For some instruments this could be done as a field or bench service by a Hach service technician. Some instruments require bench service for this and cannot be done as a field service. This cannot be done by end users. If a certificate is required for regulatory purposes to show that the instrument has been calibrated, this is what would be required.

Verify the results on the instrument are within acceptable tolerances- This can be done with either a primary or secondary standards. This generally consists of taking a measurement on the standard and comparing the result to the expected standard value. Primary standards are the best option in most cases. Secondary standards are more common in applications where primary standards are difficult to prepare. If the purpose of the calibration is to increase the confidence in results, then this would be the best way to perform that calibration.

Creation of a user calibration curve- Some instruments supported by Hach (such as pH or conductivity sensors) require more frequent user calibrations to adjust for drift. Whereas some instruments (such as colorimeters and spectrophotometers) use built-in factory calibration curves as programs that are used to calculate results from raw measurements taken by the instrument. In the case of instruments that have factory programs, customers also have the option to create a user calibration curve as a user program. This could be done to use the instrument to perform a test there is not a factory program for, or to use in place of the factory program. Creating a user program requires preparing and running several primary standards at different concentrations. For some parameters (such as Sulfate) this can improve accuracy, but for most parameters user programs can be less accurate than the factory programs. For this reason, it is not recommended for customers to create a user calibration to use in place of a factory calibration, unless required to by their regulator or otherwise stated in the method document.
 

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