What is Calibration and Why is it so Important?

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Calibration is the process of comparing a reading on one piece of equipment or system, with another piece of equipment that has been calibrated and referenced to a known set of parameters. The equipment used as a reference should itself be directly traceable to equipment that is calibrated according to ISO/IEC 17025.

ISO/IEC 17025 is the International Standard for the accreditation of Testing and Calibration Laboratories. It includes quality management system requirements along with technical requirements. In the UK, ISO/IEC 17025 accreditation is provided by UKAS. So, often calibration performed by an ISO/IEC 17025 accredited laboratory is referred to as ‘UKAS Calibration’.

How Temperature Calibration is Carried Out

In general use, calibration is often regarded as including the process of adjusting the output or indication on a measurement instrument to agree with value of the applied standard, within a specified accuracy however this is actually two processes: calibration and adjustment. It is important therefore to understand exactly what service you require. It is also important to understand what is being calibrated and how the calibration is being performed.

As an example, consider a digital thermometer that uses an external temperature probe; some calibration service providers will perform the calibration using a simulated temperature value that is applied to the thermometer only (i.e. without the temperature probe). Here, a test instrument is attached to the digital thermometer and a voltage equivalent to a specific temperature is applied to the digital thermometer. The result is recorded, and the thermometer is then considered to be calibrated.

Many users require, and  expect, a more rigorous calibration to be performed that reflects real-world usage. Here, the preferred method is to test both the digital thermometer and the temperature probe together (in other words a ‘system test’) and to use a real heat source. The value displayed by the system being tested is then compared against the standard (the system with a known or assigned accuracy from the first paragraph).

Why is Calibration so Important?

Calibration defines the accuracy and quality of measurements recorded using a piece of equipment. Over time there is a tendency for results and accuracy to ‘drift’ when using particular technologies or measuring particular parameters such as temperature and humidity. To be confident in the results being measured, there is an ongoing need to maintain the calibration of equipment throughout its lifetime for reliable, accurate and repeatable measurements.

The goal of calibration is to minimise any measurement uncertainty by ensuring the accuracy of test equipment. Calibration quantifies and controls errors or uncertainties within measurement processes to an acceptable level.

Food Industry

Within catering, or commercial kitchens, the implications of using a piece of equipment that has not been calibrated could be that a critical food temperature is incorrectly measured; this could result in:

• A food safety issue
• Breach of HACCP and customers being ill
• Environmental Health Officer notices of closure
• Legal action

All of which result in damage to the reputation of a business. The possible cost to reputation, when compared to the cost of a simple two point annual calibration, means it’s often not worth the risk of ignoring calibration.

Manufacturing

In manufacturing process applications, any equipment used should be calibrated at multiple points across its working range to ensure reliable information to critical alarms and systems. Failure to calibrate or improper calibration has been the cause of injury, death and even major environmental disasters.

How Often to Calibrate?

Consider the cost of calibration as an investment and the potential results of an incorrect reading as the cost of not making the investment.

For most industries, the standard is to calibrate annually. As you gain results from calibration tests, you will be in a position to potentially adjust the frequency of calibrations, and/or upgrade to more robust measuring instruments if needed. Most calibration laboratories supply a printed calibration certificate for the customer to retain as proof of quality standards.

In summary, calibration is vitally important wherever measurements are important; it enables users and businesses to have confidence in the results that they monitor record and subsequently control.