Instruments are designed to deliver precise measurements; however, measurement errors may accumulate over time in any measuring device. Environmental conditions, aging, wear, and general use may cause measurement errors in precision equipment. One of the most important techniques for determining the accuracy of measurements is calibration.
What Is Calibration?
Calibration is the process of checking the measurements of a device against a reference value.
The purpose of calibration is to determine whether a device is performing within its specified tolerance limits. If there is a discrepancy between the measurement results and the reference value, then the device may need to be adjusted, repaired, or examined in more detail.
Calibration does not mean setting an instrument to zero. Rather, it is the process of ascertaining how close an instrument’s measurements are to a reference value.
Why Is Calibration Important?
Accurate measurements are crucial in laboratories, manufacturing, engineering, medicine, and other fields. An instrument with inaccurate readings can lead to false conclusions, defective products, or unnecessary expenditures. By regularly calibrating instruments, you can detect measurement errors before they become serious problems.
Even a slight error in a precision instrument can significantly impact the outcome of a measurement.
Sources of Measurement Error
There is no such thing as an error-free measurement. Errors can occur due to various reasons and can manifest in different ways.
Systematic Errors
Systematic errors are errors that are always offset from the true value. Such errors can be caused by inaccurate calibration, hardware limitations, or external influences. Since systematic errors usually occur in a predictable manner, they may be detected and corrected by calibrating the instrument.
Random Errors
Random errors are errors that differ from measurement to measurement. Random errors can be caused by electrical noise, temperature fluctuations, vibrations, or other variables. By taking multiple measurements and averaging them, you can estimate the amount of random error in your measurements.
Calibration Procedure
Calibration typically involves comparing the output of an instrument to a known reference value. First, the instrument and the reference value must be prepared for the test. Next, the instrument is tested at one or more known reference values. The readings of the instrument are then compared to the reference values.
If necessary, the instrument may be adjusted to improve its accuracy. After calibration, the results of the calibration must be recorded so that the accuracy of the instrument can be monitored.
Reference Standards
The accuracy of the calibration depends on the accuracy of the reference standard used. The reference standard must have known and controlled properties. In order to establish a reliable calibration chain, there must be a hierarchy of standards with ultimate traceability to national or international reference standards.
By using traceable reference standards, it is possible to compare measurements from different instruments and laboratories.
Environmental Factors
Measurement errors can be affected by various environmental factors such as temperature, humidity, vibration, and electromagnetic interference. Thus, calibration must be carried out under specific environmental conditions or the effects of the environment must be accounted for. For example, an instrument may perform correctly under laboratory conditions but may give incorrect readings when exposed to extreme conditions.
Calibration Frequency
The calibration frequency of an instrument depends on several factors including the type of instrument, its usage, the environment in which it is used, and its previous calibration history. Some instruments require frequent recalibration due to continuous use or harsh operating environments, while others may be used for a longer period of time without recalibration.
By recording the calibration history of an instrument, the user can determine if the calibration interval should be increased, decreased, or maintained.
Calibration Records
Record keeping is an important aspect of calibration. Calibration records may include information such as the name of the instrument, the calibration standards used, the calibration results, the calibration date, the name of the technician, and the next scheduled calibration date. These records enable users to monitor the calibration status of an instrument and to analyze trends in the accuracy of the instrument.
Calibration and Quality Control
Calibration is closely related to quality control. In industry, the accuracy of the measurement instruments used for the dimensional, temperature, pressure, electrical, and other measurements directly affects the quality of the product produced. If an instrument is inaccurate, the quality of the products produced will also be affected. Therefore, regular calibration of instruments contributes to both measurement accuracy and quality control.
Conclusion
Calibration is one of the most important steps to ensure measurement accuracy. By performing regular calibration, you can determine the accuracy of your instruments and take corrective measures if necessary. When you use proper reference standards and perform the calibration under controlled conditions, and keep proper records, you can ensure that your instruments are performing as expected.