Sensors are central components of modern manufacturing processes, without which economic production would be unthinkable. Their measured values help to monitor quality, avoid rejects and form the basis for seamless documentation of the production process. This is an important prerequisite for market approval, particularly in the manufacture of medical products. In order to meet the highest quality standards, manufacturers are obliged to carry out regular calibrations and ensure the precision of their measuring equipment. In-situ calibration is an ideal alternative to cost-intensive calibration in the laboratory. In addition to reduced downtimes, this method offers the advantage that the measuring chain can be calibrated holistically - from the sensor to the cable routing of the system to the measuring and evaluation devices. To enable more manufacturers to benefit from in-situ calibrations, measurement technology expert Kistler has expanded its product portfolio and global service.

Sensors integrated directly into the production line fulfill two important tasks in the manufacture of medical products: Firstly, they continuously monitor quality-relevant production steps and ensure that the parts produced meet the highest safety standards. Secondly, they collect measurement data on quality-relevant characteristics in real time and thus lay the foundation for fulfilling the documentation requirements as stipulated by the Food and Drug Association (FDA) in the USA or the MDR regulation in the European Union for market approval. The key to documentation lies in the sensors that are installed in the production systems: They record all quality-relevant production parameters without the need for additional testing.

Precise measuring equipment thanks to regular calibrations

Over time, however, environmental influences such as temperature and humidity, but also dust, chemicals, mechanical wear or ageing can affect the precision of the sensors. Regular calibrations reveal these effects. Manufacturers can correct any deviations, detect faulty sensors and replace them at an early stage to ensure product safety and quality. Almost all common standards for quality management systems, such as ISO standard 9001 or ISO standard 13485, which has been specially adapted for medical technology, therefore stipulate regular calibration and inspection of the measuring equipment used.

However, the standards do not define the exact calibration procedure or how often it must be carried out. Most manufacturing companies therefore draw up an in-house test plan for their measuring equipment and manage it on site. This plan specifies, for example, how often the manufacturers carry out calibrations and how these are carried out in detail.

Alternative to cost-intensive calibration in the laboratory

In principle, manufacturers can choose between two calibration methods: calibration in the laboratory or on site in their own machine. If they opt for the first option, they must first remove the measuring equipment from the production machine and send it to a laboratory accredited specifically for calibrations. Such certified laboratories work according to an international standard that specifies the procedure and documentation of the calibration process - manufacturers therefore benefit from a high quality standard.

The disadvantage is that this method is particularly cost-intensive, as the measuring equipment is down for the duration of the calibration. If replacement sensors are available, the system is at least at a standstill during set-up and assembly work. If these are not available, the production system is down until the laboratory sends the sensor back. Considering that a laboratory calibration takes around two weeks on average, this results in a financial disadvantage for manufacturers that should not be underestimated.

Laboratory calibrations have another disadvantage, particularly in medical technology: the removal and installation of the sensors may make it necessary to re-validate the manufacturing process after replacing the measuring equipment. This is the only way manufacturers can ensure that the manufacturing process with the newly calibrated sensor continues to deliver the necessary precision and quality and produces within the specified manufacturing tolerances. In this case, the system is also at a standstill during process validation and incurs additional costs.

This additional effort is eliminated if manufacturers opt for in-situ calibration. With this calibration variant, the measuring equipment remains installed in the system and there is no need for installation work that could affect the process. A new process validation is therefore no longer necessary.

Calibrate the entire measuring chain

In-situ calibrations also have the advantage of eliminating assembly and set-up times as well as transportation times. The system is only shut down for the duration of the calibration. This is a significant time and cost saving compared to laboratory calibration. Because the sensors remain in the system during in-situ calibration, manufacturers can also calibrate the entire measuring chain - from the sensor to the cable routing installed in the system to the measuring and evaluation device. Measurement uncertainties caused by individual components along the measurement chain can thus be taken into account.

Due to their design, however, in-situ calibrations cannot be carried out on every system. Experienced measurement technology experts can help manufacturers to find out whether their system meets the necessary requirements for this calibration method: Is the machine capable of applying the forces required for calibration and holding them long enough to generate meaningful measurement data? Can the required load points be approached with the machine and the integrated software? Does the system offer enough space to place a reference sensor together with an adapter? Does the measurement data management system used allow the integration of a calibration process?

The measurement technology expert Kistler supports its customers in answering these questions - and recently expanded its portfolio. Kistler now offers in-situ calibrations specifically for applications in the medical environment. Trained service employees support and advise medical technology manufacturers throughout the entire process. In the first step, they check the feasibility of an on-site calibration. If the requirements are met, the experts are also on hand to assist with further preparations. Together with the customer, they define the ideal calibration process and check whether additional equipment, such as an adapter for the reference sensor, is required. They also create checklists for users. These can be used as part of the process documentation. If required, Kistler's service staff can also carry out in-situ calibration professionally using traceably calibrated reference sensors - to a uniform standard almost anywhere in the world. Manufacturers whose production sites are spread around the world can thus ensure that all their systems operate according to the same standards. The improved comparability ensures greater safety, quality and, last but not least, greater cost-effectiveness.