Calibration – The Key to Accurate Measurements

Calibration is a vital and mandatory process in the utilization of measuring instruments by any business unit. The reliability of the test results generated by an instrument is established by the calibration report of that instrument. Any laboratory involved in third party testing or Quality control of a process industry should take its calibration activities seriously.

Before presenting an exposition on the topic or subject of Calibration, it will be useful to understand the need for calibrating instruments. First of all, let us make one thing clear that we need to calibrate measuring instruments only and not those instruments or machines which do not generate any data for measurement purposes. Now, the importance of calibration stems from the fact that, in order to establish reliability in the test results we need to have some kind of verification process in place. This purpose is solved by reliable calibration services. Accuracy in a calibration process ensures accuracy in the data obtained from an analytical measuring instrument.

Before we can embark upon exploring all the details and intricacies of ‘Calibration’, we need to define it. There are a number of standard definitions of Calibration specified by various standard bodies, but simply put Calibration can be defined as the process or set of operations needed for comparing the results produced by the instrument being calibrated, with that of standards being used for calibration. These standard substances are also known as Standard Reference Materials or Calibrators, and these must be already calibrated against far more accurate reference standards which are traceable to SI units. Sometimes, calibration can also mean to configure or manipulate instruments to give values as determined by those of standards. The choice of reference standards depends on the type of instrument being calibrated, i.e. specifications (like least count), and also on the accuracy requirements of the measurement process. Types of instruments requiring calibration can range from relatively small ones like weighing balances, pressure gauges, ovens to large ones that are used in industries like automobiles etc. The type of calibrators also varies with the kind of instrument requiring calibration.

The time required for calibration varies with the type of instrument being calibrated, and also on the purpose of calibration. As a rule of thumb, the time period for a particular calibration is directly proportional to the degree of accuracy demanded. Hence, a very sensitive instrument will require longer time to get calibrated as compared to a less sensitive one. Another aspect concerning calibration is the frequency of calibration. This depends, among a number of factors, on (1) manufacturer’s recommendations, (2) tendency to wear & drift, (3) frequency and severity of use, (4) environmental conditions (like lab climate, vibrational levels, etc.) & (5) recorded history of maintenance and servicing.

Like no measurement result can be free of error and a certain degree of uncertainty is associated with it, similarly calibration reports also state the value of uncertainty involved in the process of calibration for a particular instrument. So, every test result produced by a measuring instrument has a limit of certainty defined by the uncertainty value. Calibration services are required for a number of different fields like mechanical, thermal, electro-technical, analytical etc. Ensuring calibration of instruments is the key to maintaining faith amongst customers and carrying out business in a smooth manner.