WIKA Technical Information: Methods for Improving Overall Uncertainty in Dry Well Temperature Calibration Baths

WIKA provides both fixed-point calibration and comparative calibration services, and the appropriate calibration method is determined by the accuracy requirements and the type of test item. Calibration of thermometers can be performed over a temperature range from -196°C to +1200°C. Calibration certificates can be selected from general calibration EN3.1 inspection certificates (factory calibration) or DKD/DAkkS certificates (ILAC-MRA compliant). For thermometer calibration, a calibration cycle of one year is generally recommended. WIKA also calibrates products from manufacturers other than our own. We support the calibration of electrical thermometers with transmitters, resistance temperature detectors, thermocouples, and more. Since 1982, WIKA has been a member of the German national standard calibration service (DKD) and actively participates in DKD working groups and standardization committees. Our calibration laboratory and mobile calibration services are accredited in accordance with DIN EN ISO / IEC 17025.

In Germany, ISO and ILAC-MRA accredited calibration is typically carried out at calibration testing facilities accredited by the German Accreditation Body (DAkkS). Many measurement instrument manufacturers also have such facilities in-house. These facilities operate independently of the products and perform complex calibration-related tasks. Complex tasks range from checking in-house standards to calibrating customer-specific products, such as assembled multi-point thermometers. It is also possible for customers and quality managers of calibration testing facilities to collaborate in developing the necessary calibration processes for the factory. It is essential to define situations where standard checks are sufficient, where customer-specific solutions are meaningful, or where using accredited mobile calibration testing facilities can reduce process downtime. Therefore, communication between the customer and the personnel of the calibration testing facility is conducted to define the relevant temperature points and measurement uncertainties. Following such processes, decisions are made regarding the equipment used for calibration.

Calibration of thermometers is often something that many customers cannot perform in-house. This is especially true for calibration processes certified according to ILAC-MRA certification, ISO 9001, or equivalent quality assurance systems. From a quality assurance perspective, regular checks of measuring instruments are necessary, and at the same time, traceability must be ensured. Simply put, traceability means that "in order to reliably compare measurement results, the measurement results must be able to be 'traced back' to standards (national or international) through a chain of comparative measurements." In relation to this standard, when the readings of the measuring instruments used and the measured values of the materials are compared, it becomes possible to perform calibration at a higher level. During these stages, calibration is conducted against standards that have been previously calibrated by higher precision calibration instruments. Standards are defined according to ranks established by law, which extends from working standards or factory standards to reference standards and national standards. Based on this ranking, the calibration hierarchy of the implementing organization is defined. This ranking spans a wide range, from in-house calibration testing facilities to accredited calibration laboratories and national meteorological institutes.

Calibration is not performed using the same testing method for all cases. The choice of testing method varies based on various factors such as process conditions, quality standards, and safety requirements. Depending on the testing method, it is also possible to demonstrate that the calibration item has a measurement accuracy that is twice as precise. This becomes an extremely important factor in enhancing process efficiency. Calibrating temperature measuring instruments is essential for various reasons and meanings. The calibration of thermocouples and resistance temperature detectors is becoming increasingly important in light of recent material shortages and the need for manufacturing process efficiency. Improving measurement accuracy leads to savings in materials and reductions in pollutant emissions, and the calibration of thermometers is also related to safety. For example, if the measuring instruments on a production line do not display correct values and process control is erroneous, there is a risk of accidents or quality defects. The importance of calibration is evident in everyday examples, such as household gas and water consumption meters and fuel gauges at service station fuel pumps. For these reasons, regular calibration of temperature measuring instruments is necessary to reconfirm the reliability of measurement values and to assess changes over time. When accuracy or operation becomes questionable, consider readjusting or replacing the thermometer.