What are the Methods of Calibration?

July 10, 2022
Ann Oliver

Calibration is checking whether a device measures what it’s supposed to measure. The word comes from the Latin roots “calere” (to heat) and “bulla” (a measuring vessel). It means adjusting something to measure what it’s intended to measure. Calibration is a process used to check the accuracy of temperature measuring equipment.

To check the instrument’s accuracy, we need to know what its readings should be. This reference value is called calibration.

Forms of Calibration

Calibration can be done in two ways: Primary and Secondary Calibration.

Primary calibration checks the accuracy of an instrument by comparing its reading with that of a standard measuring device or another calibrated measuring device. Secondary calibration checks a device’s performance (repeatability) rather than accuracy. In other words, secondary calibration measures how consistently an instrument gives particular measurements when it is repeatedly checked under specific conditions, such as temperature and pressure.

The most used type of calibration is Primary Calibration. It is the most common form of calibration and is done to check the accuracy and precision of a measuring instrument. There are different types of calibration, like Mechanical calibration, measuring the length of a rod or the diameter of a screw using thermodynamic calibration. Itis measures the temperature of an object by using a thermometer. Electrical calibration is measuring voltage or current in an electrical circuit. Optical calibration is the reading of an optical instrument that is checked to see if it is accurate by comparing it with another device.

Lastly, relative calibration checks the accuracy of comparable measuring instruments like a measuring tape, a micrometer, and other tools.

Calibration Instruments

Different types of equipment are needed to be calibrated, like the Digital Multi Meter (DMM).
They are used to test electrical circuits, appliances, and electronic devices. DMMs have various features such as a Digital display for easy reading and measurement, an Ammeter to measure resistance and voltage, and a D.C. Voltage measuring electrical voltage and current. In pressure calibration, there is a gauge and an adapter.

The indicator is used to measure the pressure, and the adapter is used to connect the indicator to check the accuracy of pressure gauges. In temperature calibration, they are used to measure the temperature of an object by using a thermometer. Calibration is done on weighing machines to test the length of a rod. At times the diameter of a screw by using a micrometer. A calibration instrument has unique features, such as a dial indicator to check the accuracy of the dial indicator.

Accuracy used in Calibration

Accuracy is the degree to which an instrument is free from error. It is measured by comparing the measured value of a calibration standard (known to be accurate) with the actual value of the same standard. Calibration Standards are used to check the accuracy of measuring instruments. They are also known as “reference standards” or “master standards.” Calibration standards are calibrated by an accredited laboratory using a standard procedure that measures the accuracy of a device (measuring instrument) over a range of conditions in which it is expected to perform accurately, such as temperature, pressure, vacuum, or radiation.

Calibration Standards can be either liquid or gas-based, depending on their nature. For example, Gas Standards like Nitrogen (N2), Helium (He), etc., and Liquid Standards like Mercury(Hg), etc. Instruments are calibrated using procedures that consider the device’s accuracy and precision. This procedure is carried out by an accredited laboratory or by using a process that ensures that measurements are accurate and precise within specified tolerances.

The calibration standard is prepared by mixing accurately known amounts of each substance with the instrument being calibrated. After completing the calibration procedure, the calibration standard is carefully weighed to determine its mass. It is compared with the calibration standard to check whether the instrument has been correctly calibrated. If it does not match exactly, then it must be rechecked before recalibrating for use on another job site or at another location where conditions may differ from those at which it was initially calibrated.

Importance of Calibration

Calibration is necessary to get accurate measurements. Calibration is done to check any errors in the instrument, such as temperature, pressure, vacuum, etc. Without calibration, measurements cannot be trusted as accurate or reliable.

When properly tested and adjusted to ensure accuracy, most instruments can be used for months or years without recalibrating. A calibration certificate is issued from the calibration authority. This document certifies that the instrument under test has been calibrated to the required accuracy and precision. A calibration certificate is issued by the calibration authority.

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