Calibration of an instrument involves comparing the measurements of two instruments, one which has a known magnitude (also known as the standard) against the instrument whose unit measure is under the test. The calibration standard must be more accurate than the instrument under test.

Calibration establishes a relation between a) the quantity values with measurement uncertainties provided by the measurement standards, and b) corresponding indications with associated measurement uncertainties of the calibrated instrument or secondary standard. You can use this information to establish a relation for obtaining a measurement result from an indication.

Importance of Regular Calibration

Regular calibration of instruments is necessary as the accuracy of their measurements start to drop over time. You have to make sure the instruments don’t get ‘out of calibration’. You will observe that the accuracy of major components of instruments like voltage references, current shunts and input dividers will start to shift over time. However, this shift is minor and wouldn’t affect the measurements if you maintain a good calibration schedule as it will find and correct the shift.

Calibration of instruments must be done at accredited laboratories. There are a number of risks of not calibrating, some of which include —

  • Compliance and safety issues
  • Wastage of resources and raw materials
  • Low quality of the final products
  • Increased downtimes
  • Litigation issues

How Often Should You Calibrate

You are aware that you must calibrate the instruments regularly, but how often do you have to calibrate them? You don’t have a ‘one-size-fits-all’ kind of an answer to this. Every instrument has different calibration frequency requirement. Let us see how you can approach this aspect and how you can send in the instruments for calibration services.

  • Follow the calibration interval recommended by the manufacturer

Every manufacturer recommends when you must calibrate their tools. Keep up with their recommended frequency, but also remember that critical measurements may require different intervals.

  • Before you start a major critical measuring project

If you have to carry out highly accurate measurements for a project, decide which instruments you will be using for the testing. Once you have the list of instruments, send them out for calibration and do not use them until the test. Keeping them on a ‘lock down’ till the testing begins will ensure that you get absolutely accurate results.

  • After a major critical measuring project ends

It is important to calibrate instruments before a major critical measuring project; however, it is equally important to send the same instruments for calibration after the project is finished. Once the calibration is done post project, you can confirm the accuracy of your testing results for that project.

  • After an unforeseen accident

If your instruments took a hit, like a sharp physical impact or if something knocked out the internal overload, you must send them out for calibration. At the same time, you must have the safety integrity checked as well.

  • As per project requirements

Every project and measurement job has a different calibration requirement. Some may require certified and calibrated test equipment regardless of the project size, and some may not require stringent calibration standards. These requirements may not be explicitly stated, which is why you must review the specs before the test.

  • Monthly, quarterly, or semiannually

If you use certain equipment for critical measurements often, it would be ideal to have a shorter time span between calibrations. Depending on their usage, you have to calibrate equipment on a monthly, quarterly or semiannually basis.

  • Annually and biannually

If you carry out a mix of critical and non-critical measurements, annual calibration would be a good option to choose. Biannual calibration is ideal if you carry out critical measurements and do not expose your meter to an event, as calibration at lengthy frequencies can be cost-effective.

Don’t consider calibration as an action that merely fine-tunes your test instruments. Calibration ensures that you can use equipment safely and reliably. You will always get precise results when you use calibrated test equipment. You can thus consider calibration as a form of quality assurance.