Correction – compensation for an estimated systematic effect
Correction Factor (CF) is a value that we either add or subtract to compensate for the error from a systematic effect. This correction factor is based on “Correction” from a calibration result calculated using the equation:
From the statement that “ No measurement is perfect“, the correction factor is also just an estimate even though we see it as an exact value of the compensated error (systematic error).
There are other ways to compensate for an error but this is the simplest when it comes to the reported results in a calibration certificate.
Correction Factor is sometimes known as “corrective factor” and “calibration correction“
Why do we need to calculate the correction factor?
“You cannot perform adjustment if you do not know the corrections you need to apply”
One very important reason we perform calibration is to determine the error and at the same time, the corrections to correct the error afterward.
Errors can only be detected by performing calibrations. But once an error is detected, we should do something about it. It is either we adjust (using the provided zero and span error adjustment) or perform a correction factor if we cannot adjust it.
If there is a ‘correction factor and you do not know how to apply it, then you did not fully use the actual application of calibration, therefore calibration results become useless in our process application.
If you want the best results from a calibration result, then you need to learn the technique of determining the proper correction factor.
This is one reason we need to review the calibration or measurement results from a calibration certificate– to determine if we need a correction before we can use the value from the calibration result.Another reason why we need to calculate or use a correction factor is to ensure that we meet the specified requirements of our calibrated reference standards or reference materials. We need to ensure that we use an updated correction factor every time a recalibration or new calibration takes place. This is a requirement under clause 6.4.11 of ISO 17025:2017 which states that “When calibration and reference material data include reference values or correction factors, the laboratory shall ensure the reference values and correction factors are updated and implemented, as appropriate, to meet specified requirements.”
Important Use of a Correction Factor in Measurements
Correction Factors compensate for the error that we encounter during calibration. The following are some of the important reasons why we need to use the Correction Factor, these are:
To make a measurement closer to the true value.
To adjust a measurement value that cannot be adjusted physically or by any software
To return equipment performance to a tolerable result or to a more accurate condition closer to the standard value
To reduce the effect of a systematic error.
What are these Systematic Errors that we need to correct?
Systematic errors are the errors that are known or unknown to us, known errors can be corrected or compensated. It is a consistent deviation in measurement. These systematic errors are from:
Measurement procedure -Positioning or setup and execution of methods during calibration
Effect of environmental conditions– Instruments operating in harsh or variable environments may experience systematic errors due to external factors such as electromagnetic interference, humidity, or pressure.
Personal error due to habits or improper training of the observer
Errors directly from instruments or the ‘Bias’– uncorrected errors from calibration standards can introduce systematic errors. Regular verification and recalibration of standards can help address this issue.
Instrument error from improper calibration
Zero Error – occurs when the instrument’s reading is not zero when the input or measurement signal is zero.
In every correction that we perform, remember that this is not also perfect, measurement uncertainty still exists, therefore, measurement uncertainty should still be considered.
