Calibration makes use of a standardised measurement device to adjust the measurements of the unit being tested in order to improve the accuracy of this 'unit under test'. Every instrument that measures can be calibrated but the frequency and method of calibrations differ widely.Instruments that most often require calibration are those used in precision environments (laboratories and micro-manufacturers) and in environments with a higher than usual safety requirement. While properly calibrated instruments show reasonably accurate results it is widely accepted that real world results cannot be 100% accurate with every measurement. This leeway for inaccuracy is known as the 'engineering tolerance' and provides a guide to the practical use of an instruments measuring range by defining what sort of variability is acceptable because it does not compromise the performance of said instrument.
Engineering tolerance for the calibration of instruments varies by region and application and quite often will be defined by the instrument manufacturer in terms of:
• measured tolerance
• calibration interval
• environmental range of use
• storage
Calibration Engineers make use of complex equations and testing equipment in order to ensure that the accuracy of an instrument conforms to acceptable 'accuracy ratios' which compare the standard output of their test equipment to the data measured by the unit being tested. While just about 'anyone' could technically speaking calibrate an instrument is it best to make use of a specialist for a few reasons.
The benefit of experience allows the engineer to diagnose connectivity issues that may be influencing your final reading. The connection between a device and the 'standard' can be impeded for example in an electronic calibration which involves analog components may be inaccurate due to cabling problems.
Apart from this, the success of a calibration can rely on the willingness of the individual involved to investigate small irregularities. A degree of randomness is sometimes necessary to find inconsistencies in measurements and an experienced calibration expert will often have fine-tuned their testing techniques for the best real-world results within an acceptable framework. Test methods are often defined by a region's requirements and need to conform to certain government-industry measuring standards. Experience and judgement can go a long way to ensuring that acceptable ranges are being measured and to avoid potential penalties.
Different machinery will have different engineering tolerances and in cases involving more complex units the key functions will be prioritised and calibrated. Consistent and systematic calibration is both necessary and costly. A calibration service plan with a company that specialised in your particular applications is generally the most affordable long term solution to such maintenance. Establishing a relationship with a reliable supplier will gain you the benefits of outsourcing with the advantage of dealing with individuals who acquire and intimate knowledge of your internal systems. It is worth noting that such services can sometimes be performed on-site or off-site in what is known as workshop or bench calibrations. Bench calibrations will often be performed when a controlled environment is called for.
The use of seals is also used to ensure that there is no undetected access to the instrumentation settings in between calibration periods. Such seals can contain information relating to the most recent calibration as well as a recommended interval to the next 'servicing'.
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