Calibration can be termed as evaluation and adjustment of an instrument with the aim of maintaining precision and accuracy of the measurement equipment. As such, proper calibrated instrument ensure people work in a safe environment and have access to valid data even for future use.
Purpose of Instrument Calibration
Instrument calibration allows users to eliminate or reduce chances of biased instrument readings along the range that the instrument is standardized with. This process also ensures there is consistency and continuity in values. Consider precision as defining the degree of repeated measurements to which same measurements are recorded with the same device under unchanged conditions. Therefore, it is important to note that reference standards should be used when selecting the precision test to be used or the range of interest. As for accuracy, which is the degree of closeness of recorded measurements in relation to the actual true value, there arises a functional relationship that establishes the reflected value with the standard value.
In most cases, instruments require correction for bias or when instruments act as surrogates. In the first scenario, the instrument is first set in the same units as the referencing standard. This is because the process aims at identifying and eliminating biases within the instrument relativity as defined by the unit of measurement. For instance, optical imaging systems used to measure the width of lines specifically on semiconductors use micrometers as their standard unit. However, these instruments are to be calibrated as the reference standards that the industry has laid out as the standard units for width lines in the industry.
When instruments act as surrogates, it means that the instrument uses a different standard unit other than the reference standard. As such, calibration could play a role in converting the instrument readings to the standard unit. For instance, a densitometer serves as a surrogate for measuring radiation dosage. Since the reference standards go by what a radiometry uses, the densitometer measurements are irradiated at particular dosage levels to ensure its measurements are in line with those of the radiometry. As such, when calibrating a densitometer, the calibrator considers the readings as per what the standard unit considers the optimum sterilization condition as required for medical devices.
Basic Correction of the Instrument for Bias
Calibration works the same way for instruments acting as surrogates as well as those needing correction from bias. As such, the basic steps for this process are:
• Selecting reference values within acceptable standard units with an aim of covering a range of interest.
• Carrying out measurements using the standard units on the instrument.
• Identifying the functional relationship between known values and actual reflected values keeping in mind the use of a calibration curve.
• Lastly, correcting the measurements by inversing the calibration curve.
It is important not to confuse a field check from calibration as some are in the habit of doing. A field check consists of two instruments reflecting the same reading. Nonetheless, these results do not necessarily dictate that the instruments are calibrated. For example, when a thermometer always reads 25 degrees higher, such an error is not eliminated by simply taking averages since the error is constant across the range of interest. However, one could determine its accuracy and fix it by sending it to a calibration laboratory. In line with that, it is always good to have more similar thermometers, which are used to make the same measurement. If the reflected results among the thermometers show a significant difference, then these thermometers are flagged for inconsistency and a test from the laboratory will correct things quite easily.
When Should Instruments be calibrated?
Consider major critical measurements a red flag to ensuring the instruments are calibrated before use. Additionally, it is important to calibrate these instruments even after use. This not only helps to ensure the data to be collected or already at hand is accurate, but it also means the instrument is in right condition even when it stayed long before use.
There are cases where the instrument falls or is repaired. In such events, consider calibrating the instrument before use. Accidents are a common way of throwing the instrument off balance, and it is important to do a calibration to ensure accuracy and precision are restored.
When observations appear questionable, consider sending the instrument for calibration. There are instruments that require certificates before use. Ensure these instruments are certified. Most manufacturers recommend an instrument to be calibrated within certain period. Always check the schedule for calibration to ensure the instruments are taken care of in good time.
Assume that you are about to publish a paper, and once the paper is submitted and the peer review board realizes that your readings were wrong, that would adversely affect your reputation in the field and definitely decrease your chances of being a reliable source in the future. Always ensure your instruments are calibrated in time.