Modern manufacturing uses many different tools to fabricate products, validate that they were manufactured according to their design, and assure users that they comply with any applicable standards and specifications. Only when properly calibrated can a tool be depended upon to accurately and reliably manufacture products and validate their features.
However, not all tools need to be calibrated. Mechanical tools such as dies, drills, hammers, and screwdrivers do not require calibration because they do not produce measurements. As such, only tools that produce measurements need regular calibration.
Calibration is a process whereby measurements produced by a tool are compared against standardized measurements of known accuracy which meet the calibration standard that the tool must reach. If a tool is out of specification, adjustments must be made to return the tool to its original performance and accuracy. It is good practice to take another measurement after adjustment to verify that the tool is within specification.
Calibration serves two purposes:
Over time, tools degrade due to wear and tear, overuse, or improper use. Their measurement output tends to ‘drift’ as a result, meaning they become less accurate and less reliable. Calibration ensures tool accuracy and is a requirement for organizations that want to achieve or maintain ISO 9001 certification.
Calibration has several overarching effects:
In addition to the above benefits, tool calibration contributes to:
Calibration does not guarantee product quality or process performance, but it can be a contributing factor. It controls for the accuracy of tools to instill confidence in their outputs.
Tool calibration can be performed by a laboratory that is ISO/IEC 17025 certified or internally. Simple tools like calipers, micrometers and indicators can be performed internally. Any master that is used to calibrate other gages must be calibrated and replaced (if worn) in accordance with ISO/IEC 17025. Only laboratories that are certified to this standard will be able to issue a valid calibration certificate. Using laboratories that are not ISO/IEC 17025 certified puts the accuracy of the relevant tool’s measurements in doubt.
Calibration certificates issued by laboratories may look different but they should all contain the following basic information:
There is no universal standard for the frequency of calibration. Calibration frequency depends on many factors like the type of tool, its frequency of use, and the environment in which it is used. ISO 9001 does not specify calibration periods but requires a calibration register that identifies each tool, its calibration frequency, and verification that a tool was calibrated on schedule.
The following criteria should be considered when determining calibration frequency:
The tool manufacturer’s calibration frequency recommendation. Some manufacturers will specify that calibration should be performed after a predefined number of use cycles.
The tool’s measurement history stability. If tools are regularly checked and the results recorded, inconsistencies or significant deviations from the calibrated measurement can be easily identified.
The importance of the measurement being taken. If the tool is just used to measure reference dimensions that are not used to validate the accuracy of products, calibration is less critical.
Risks and potential consequences. In conjunction with number 3 above, the accuracy of some dimensions is more important than others. If an inaccurate tolerance has no significant consequence on the final product, the tool involved does not need to be calibrated as often.
Different industries have different reasons for calibrating tools.
Calibration gives buyers and sellers confidence that they are getting properly compensated for their trades. Those trading in commodities like oil, gold, mineral resources, and many other products need reliable measurements to confidently run their organizations. In everyday life, calibration means motorists don’t have to worry about whether they are receiving the full amount of fuel indicated on the pump.
Very few people would have confidence in their medications if the ingredients used to make them were not accurately measured. Many medications must be produced under tightly controlled temperature and humidity conditions. Calibration gives billions of people assurance of their medicine’s effectiveness.
The best example of the importance of medical calibration is the pacemaker. It is directly connected to a person’s heart, giving them life. Each pacemaker is carefully tested and measured during development and manufacture. Calibration ensures that those tests are accurate, giving the user confidence that it will remain reliable long after it is implanted.
The importance of calibration on a grand scale gets good context when considering the transport industry. The thousands of parts that make up airplanes, cars, trucks, ships, and trains are manufactured to tight tolerances by many different manufacturers. Calibration ensures that the measurements and process parameters remain within tolerance so that the final product can be assembled without difficulty.
The international space station is a great example of the importance of calibration. Many of its parts are in contact with the extreme cold of space, the intense radiation of the sun, and the warm conditions of the interior living environment. Sensors that monitor the internal and external temperatures must be calibrated to ensure they provide accurate information to any monitoring and control systems. Plus, the material properties must be consistent so the manufacturers can account for thermal expansion and contraction.
The consequences for a catering company if they use uncalibrated kitchen appliances can be dire. Apart from the potential financial impact of lawsuits, poorly calibrated temperature sensors may result in undercooked food. In the worst-case scenario, customers may become ill or even die from food poisoning. Calibrated catering equipment gives staff confidence that measurements of temperature-sensitive foods are accurate and reliable.
Even though calibration is not mandatory for each tool in every organization, it is critical wherever the measurements are important. Calibration gives businesses and users confidence in their equipment, helps to maintain compliance, curtail costs, minimize downtime, reduce safety risks, and ensure customer satisfaction.