Did you know that irregular calibrations of your gauges can be very detrimental to your process? ELPRO LEPENIK Calibration Laboratory answers all your questions in this expert article
Calibration is a set of operations to determine the difference between the reading of a measuring system and a reference value. The calibration determines the correction of the measuring system.
Below we answer an important question closely related to the accuracy of your measuring instruments and the related quality of your applications and processes – “How often do we need to calibrate and what is the recalibration period?”
There is no simple rule on how often to calibrate. It is the user of the benchmark who knows best where it is used, who uses it and, last but not least, how it is used. But it is good to ask the following question. What will be the consequences if the benchmark is inaccurate?
Different instruments have different uses. Desktop meters that measure room temperature or humidity are not subject to large fluctuations in temperature or humidity, so are less likely to give inaccurate readings over time than those used at the extreme limit of performance. The instrument may even be used at the lower and upper extremes. The biggest risk is exceeding the manufacturer’s limits. This increases the risk of the instrument malfunctioning and requires immediate recalibration. This brings us to the first condition for determining the frequency of calibration. Am I using my benchmark at the extremes of my capacity?
Each criterion has a defined lower and an early upper limit of the working range. If the instrument is used close to these limits, the interval between the two calibrations is reduced, as the measure is more likely to become inaccurate.
If the instrument is used in a harsh environment where there is a lot of dust, steam, high humidity, its accuracy may be reduced. This is especially true for electronic instruments. If an instrument with a digital display or any other digital part of the gauge is used in a demanding environment, there is a greater chance of erroneous measurements. This brings us to the next question about the frequency of calibration. What are the working conditions under which I use my benchmark?
Drift is the difference between the corrections at a point between two calibrations.
If we have two calibrations with the same calibration points, we can determine the drift of the instrument. The smaller the drift, the more accurate the instrument, the more we can trust its measured values. So we can ask ourselves the following question. What is the difference between the same calibration points between two calibrations? If the calibration results in a gauge with corrections that differ significantly from the previous calibration, it is worth considering changing the gauge.
Accidents happen everywhere. Even among the most controlled processes. The next question is, was there a bump with the meter, did it fall off? If yes, then recalibration is a must, as the gauge can no longer be trusted.
Calibration is recommended when using a new meter for the first time. Even if it is new, it does not mean that it is accurate, and we do not know its actual correction.
The most common calibration interval is 12 months. It is then up to the user to determine if this interval should be reduced or increased, based on the questions above. With an interval of more than 12 months, it is indeed very difficult to follow the developments of the benchmark and to predict its expected drift.
The figure shows the corrections of two calibrations. The difference between the corrections between two points is called drift or creep. The figure shows the expected and uniform creep of the thermometer between two calibrations over the whole range. The smaller the creep, the better the thermometer.
For the rest Frequently Asked Questions related to the topic, please contact our QA.
☏ Call us: +386 2 62 96 720
They are always available for opinions and explanations:
Aleksandra Lepenik, expert in temperature measurements
Measurement expert Zoran Lepenik
More information at: https://www.elpro.si/elpro-laboratorij-za-kalibracije/
Author Blaž Tomaž Vertačnik
February 2023
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