Calibration, calibration, and adjustment all have to do with precision and measurement. However, the way of proceeding and therefore the accuracy that can be achieved are very different.
Calibration involves comparing a product to a national reference standard, such as the “standard kilogram”. Originally, a platinum-iridium cylinder was kept in a safe in Paris until 2019. Since then, the kilogram, as well as the meter, has been defined by a natural constant. Indeed, the exact value of the kilogram is now formulated from Planck’s constant, which links the energy of a light wave to its frequency and which always has the same value. By its unit of measurement [kg m2/s], Planck’s constant is clearly related to the kilogram and therefore to the meter and the second.
Calibration is the legally required verification of test equipment to maintain the prescribed measurement values in accordance with the Measurement and Calibration Act. Public bodies, in this case, weights and measures offices, are the only ones authorized to carry out calibrations.
In addition, only measuring devices whose model has been “admitted to verification” during a certification procedure can be calibrated. In general, the Calibration Act was passed to protect consumers. Thus, all measuring devices whose results are converted into a monetary value vis-à-vis the customer are subject to a verification obligation. These include, for example, pressure balances.
Calibration consists of having the display of a measuring device compared with a reference device or a standard or reference by a calibration laboratory. In other words, during calibration, a calibration laboratory makes a comparison between the theoretical value and the actual value.
The calibration result is documented on the calibration certificate, which further contains information on the calibrated object or the device under test, the reference frame(s), the verification apparatus, the verification procedure, and ambient.
Conditions during calibration. Calibration does not constitute a permanent intervention on the measuring device.
The quality management standard DIN EN ISO 9001 prescribes the management of measuring instruments and their regular verification. However, for financial reasons, an ISO สอบเทียบเครื่องมือวัด calibration is often carried out on measuring devices whose effect on the final product is small or medium. All ISO calibrations fulfill the following points:
- Traceability of benchmarks against national and international standards Annual calibration of benchmarks
- A detailed description of the measurement method and, if applicable, of the standard/directive applied
- A warm-up time of at least 4 hours in the calibration laboratory
- Documentation of ambient conditions
- Double-check of measurement results
- Interpretation of the measured values with the tolerances indicated by the manufacturer
Unlike calibration or calibration, adjustment always constitutes a lasting intervention on the measuring device by the calibration laboratory. The adjustment consists of determining the exact value using a measuring device with a known reference. The measuring device saves the adjustment value and takes it into account during the next measurement. Depending on the measuring device, one or more measuring points can be adjusted by the laboratory.
The adjustment takes place partly with a potentiometer and partly also via a menu or PC software. Since the adjustment is a permanent intervention on the measuring device, it must be recalibrated after the adjustment (“as left”), if an adjustment is necessary following the first calibration (“as found”). This calibration service is the only way to ensure full traceability of all measurement results and to detect measurement errors during calibrations.
But what exactly is calibration?
According to the International Vocabulary of Metrology, calibration is an “operation which, under specified conditions, initially establishes the relationship between the values of the quantity with the uncertainties of measurement derived from the standards and the corresponding indications with the uncertainties associated measurements and, in a second step, it uses this information to establish a relationship in order to obtain the measurement result of an indication.
In other words, calibration is the procedure by which the reliability of measuring instruments, such as a balance or a weighbridge, is tested and guaranteed.
Using standard weights that are subject to strict control and certification, a calibration subjects the weighing equipment to various tests and, in the end, defines the result that it must present in the presence of an object of that mass.
Performed by entities certified for this purpose, the calibrations offer a guarantee that the scales and weighbridges operate with the desired and expected precision.
The importance of calibration
Calibration consists of using a standard to determine the relationship between the value displayed by the measuring instrument and the true value. The calibration of a measuring instrument by means of a standard makes it possible to guarantee its reliability.
As a rule, calibration is performed twice: before and after using the measuring instrument. If the measuring instrument is used continuously and calibrated periodically, the time between each calibration must be determined beforehand and strictly observed. This delay is called the “calibration interval”. To determine the interval, it is advisable to refer to the manufacturer’s recommendations while adapting them to the frequency of use of the instrument.