ELPRO LEPENIK Calibration Laboratory In this expert article, we introduce you to the importance of calibration for your instruments and the impact it has on the elimination of deviation.
Calibration is the process of determining the deviation between the measured values of a measuring system and a reference value. It is the execution of a series of operations that allow the correction of the measurement system to be detected and corrected. Measuring instruments are always exposed to the environment, so proper handling and preparation of the environment and the device itself for calibration is crucial. It is important to note that calibration does not involve adjusting the gauge to an exact value, which is another area. When adjusted, the gauge is adjusted to achieve a precise value at specific points, thus eliminating the need for correction. However, the correction can also be taken into account manually or mathematically on the basis of certificates.
Calibration is important because it gives us information about the state of the gauge and its performance. By checking the drift, which is the difference between the corrections at each calibration point between two calibrations, we can observe any drift of the measurement value from the true value over time. Although drift is usually small, it can have a significant impact on the operational chain of processes, causing consequences and costs.
The calibration certificate allows us to diagnose the condition of the gauge and determine whether it is still working within the desired parameters. The certificate can be used to judge whether the instrument is still fit for use. Comparing past calibration results also allows us to predict future performance, so regular and frequent calibration is particularly important. It is also essential that calibration certificates are respected when using the instrument.
The choice of calibration points and the need for single or multi-point calibration depends on the specific application and the range of use of the instrument. In general, it is advisable to perform several calibration points, as this allows us to obtain a more complete and meaningful gauge state.
Multiple calibration also allows us to obtain information about the response of the scale in the process used over the long term. A single point calibration may not cover all important aspects of the gauge’s performance, so it is better to calibrate at several points within its range to get a more accurate picture of its performance. This approach allows us to check more reliably the linearity, sensitivity and possible bias in different parts of the measurement range.
The development of moisture measurement has brought significant changes and a variety of sensor types with different operating principles. Among these sensors, capacitive sensors prove to be accurate and reliable over the entire humidity range, from 0% relative humidity (RH) to 100% RH. For example, Vaisala’s humidity sensors have proven their worth even in challenging environments such as Mars.
Differences between sensors and their technologies stem from a variety of factors, including their specific operating principles and sensitivity to environmental influences. All environmental conditions can affect the potential of the sensor and, as a consequence, cause drift or a delay in the measurement signal. Certain sensor technologies are more prone to react faster or less well to environmental changes, increasing the chance of drift. On the other hand, some technologies show less sensitivity to these changes, allowing more stable sensor performance over time.
Measurement uncertainty is an estimate of the total range of possible deviations between the measured values and the true value of the quantity measured. This is the result of taking into account the various influences that can contribute to measurement uncertainty. Even in very stable environments, calibration uncertainty is usually the most important factor contributing to the overall uncertainty of the final measurement result. There are many parameters that can affect the measurement, including ambient temperature, room pressure, vibrations, the influence of connecting conductors and even altitude in the case of certain measurements.
It is essential to ensure traceability of measurement back to the SI (International System of Units). The further the measurement system is from the primary standard (reference definition of the quantity), the greater the measurement uncertainty. Calibration laboratories shall use instruments with the lowest uncertainty of measurement, as close as possible to the primary standard, to ensure traceability of the measurement. Although calibration can be carried out anywhere and in different ways, this usually leads to greater measurement uncertainty and is not sufficient to be properly considered in certain applications. For globally recognised calibration with minimum uncertainty of measurement, a laboratory shall be selected that performs accredited calibrations in accordance with ISO/IEC 17025. This standard ensures that calibrations are carried out under strictly controlled conditions with minimal interference, ensuring maximum reliability and traceability of measurements.
When setting the price of calibrations, a key factor is the intended use of the measurement results. Accredited calibrations usually represent a higher cost, but provide higher reliability and lower measurement uncertainty. In addition, accredited calibrations can be performed with multiple calibration points, allowing more detailed information on the performance of the measurement system. Despite their higher cost, they often prove to be better solutions in situations where accuracy and traceability are crucial.
It is a key element in product choice. More expensive instruments tend to have a longer lifetime and a tendency to be delayed, e.g. buying more of the cheaper criteria over the same time span. The longer the intended long-term use, the lower the initial investment
In the case of moisture measurement: depending on industry/sector requirements. The measurement technology in the meters is important. The overall metering ecosystem is an important factor (e.g. connections and other meters, often elements from the same manufacturer, facilitate communication between the different parts).
If one sensor is used on one display, then separate calibration (meter and tap) is not necessary. The display must be calibrated separately when several different temperature sensors are used on one instrument. For displays, it is important to keep them in good physical condition, i.e. the outside of the meter. Dirt and physical damage can have a significant impact on measurements and should be checked regularly.
In the same way as planning production, workflow or plant, it is recommended to set up a plan for controlling measurement equipment. Sometimes this means out-sourcing or. outsourcing, which can be more convenient and reliable if you choose suitable laboratories. Often the parameters that can be measured are the ones that are crucial to the whole process, so it is important to choose a sufficiently credible laboratory to carry out the calibrations.
When the need arises to check the accuracy (of the process/device), calibration is carried out. “Just think how many correct measurements can be made, how much energy/costs can be saved and how many quality end products can be delivered by regularly maintained and verified equipment.”
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They are always available for opinions and explanations:
Aleksandra Lepenik, expert in temperature measurements
Measurement expert Zoran Lepenik
Author.
May 2023
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