What’s the difference between Calibration and Adjustment?

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We get this question a lot, and it is a commonly misunderstood or misinterpreted topic. Here are a few Frequently Asked Questions that will help to clarify the matter. Thanks to Master Calibrators for the assistance in drafting this article. 

What is Calibration?

The most basic reason for calibrating an electrical instrument is to ensure that it is reading accurately. This is done by comparing the Instrument Under Test (IUT), to a Calibrator of known output and high accuracy which is known as a ‘Standard’. The second device is known as the Instrument Under Test (IUT), which is the clients electrical meter/s. When performing an electrical calibration, one makes a comparison between a Standard (Calibrator) and the Instrument Under Test (IUT) and records the results. These results are provided to the owner of the IUT, generally with Pass/Fail advice for each function of the electrical meter. The Pass/Fail is given according to weather results are within the electrical instruments (or electrical meters) manufacturers advised calibration tolerances or not.

What exactly is checked during a calibration, and what functions should be calibrated?

Electrical Calibrations include calibrations such as; multimeter calibrations, scope meter calibrations, clamp meter calibrations, insulation resistance meter (Megger) calibrations, PAT Tester calibrations, RCD Tester calibrations, Power Logger calibrations and anything else reading electrical data. Information and functions calibrated on these meters include such things as; Current, Voltage, Resistance, Frequency, Scope / Bandwidth, Temperature, Loop Impedance, Continuity to name just a few. The entirety of a meter’s functions should be calibrated, this means a variety of tests at a variety of values, for each different function available on the meter.

Is checking and calibrating the same thing?

Calibration is not the equivalent of using a check box or calibration box supplied by some electrical meter manufacturers. These are simply function check boxes, the purpose of which is purely to ensure the meter is functioning at all. They do not confirm that the electrical meter is reading accurately or within tolerance. They are also not accurate enough to act as a Standard as defined above in ‘What is Calibration’.

Does calibrating mean adjusting readings?

Calibration is sometimes incorrectly regarded as the process of adjusting the IUT so the measurement will agree with the measurement of the standard, within a specified accuracy. Calibration does not mean adjust, it just means, as described above – to compare, and to make sure an IUT is within manufacturers’ spec. Adjusting electrical instruments would be more accurately referred to as metrology or even repair if it involves the replacement of components.

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