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Calibration is the process of evaluating and adjusting the precision and accuracy of measurement equipment. Proper calibration of an instrument allows people to have a safe working environment and produce valid data for future reference.
Calibration refers to the act of evaluating and adjusting the precision and accuracy of measurement equipment. Instrument calibration is intended to eliminate or reduce bias in an instrument's readings over a range for all continuous values.
For this purpose, reference standards with known values for selected points covering the range of interest are measured with the instrument in question. Then a functional relationship is established between the values of the standards and the corresponding measurements. There are two basic situations:
The calibration method is the same for both situations stated above and requires the following basic steps:
Some people mix up field check and calibration. Field check is when two instruments have the same reading; this does not mean they are calibrated; it may be that both instruments are wrong. Let's use thermometer as an example; if a thermometer always read .25 degree higher, this error can not be eliminated by taking averages, because this error is constant. The easiest way to determine if it is accurate and fix it is to send the thermometer to a calibration laboratory. Another way to reveal constant errors is to have one or more similar thermometers. One thermometer is used and then replaced by another thermometer. If readings are divided among two or more thermometers, inconsistencies among the thermometers will ultimately be revealed.
Figure 1: For instance, the pH electrode used in titration experiments must be calibrated before the beginning of data collection.
Let's say if you are going to publish a paper and you submitted the paper with data obtained from an uncalibrated instrument. What if someone repeated you experiment and find out that your result is wrong? This will hurt your reputation in the field, decrease the reliability on your future works. Another example, if you are going to work with a chemical that will explode when it gets in contact with air temperature above 50°C. So you adjust the room temperature before you start working, then check the temperature with an uncalibrated thermometer. If the termometer gives a lower temperature than the true temperature, then you will be working in an unsafe environment. This example may be unrealistic, but there are many chemical and substance out there that require accurate and precise measurements in order to provide others a safe working environment.
This material is based upon work supported by the National Science Foundation under Grant Number 1246120