Question 1

Why do measuring instruments used in industrial processes need to be calibrated?

Accepted Answer

There are various reasons; however, all of them reflect the necessity:

Legal or company-specific regulations, such as quality and energy management, stipulate regular calibration.
The accuracy of any measurement deteriorates over the operating history due to temperature or pressure variations, shock and vibrations or mechanical loss.
Safety-relevant as well as environmental aspects can be taken into account through measures of calibration.

Question 2

Which standards require calibrations or verifications?

Accepted Answer

Today, there are many standards containing requirements regarding calibration or verification to ensure lasting product quality and to avoid product recalls. We present to you some well-known standards that explicitly refer to the necessity of calibration.

		Quality management systems - Requirements ISO9001
		Quality management system requirements for automotive production and relevant service parts organizations IATF 16949
		Medical devices - Quality management systems - Requirements for regulatory purposes ISO13485
		Retail and Food Service HACCP
		Environmental management systems - Requirements ISO14001
		Primary packaging materials for medicinal products - Requirements ISO 15378
		Occupational health and safety management systems - Requirements ISO 45001
		Energy management systems - Requirements ISO50001

Question 3

How often should my sensor be calibrated?

Accepted Answer

Calibration intervals are based upon application risk assessment and vary depending on application and regulations. Many industries and applications typically require calibration verification annually as a basic statement on frequency.

Question 4

Why should I send my device to a laboratory for calibration?

Accepted Answer

The calibration of devices sent to a laboratory is a common approach to the calibration of sensors.
We at ifm have had our laboratory accredited according to ISO17025 and can thus ensure optimum laboratory and reference conditions. By means of wet calibration, we are able to simulate real conditions and those critical process parameters that are relevant to your processes. Also, our test rigs are designed so as to cover small and large measuring ranges.

In case a device is indeed found to be out of tolerance, there is no need for you to worry about it. We can provide you with a suitable replacement device at any time to ensure your processes will not be negatively affected.

Question 5

Which criteria are important in calibration?

Accepted Answer

Basically, there are 3 criteria in the context of measurement uncertainty that allow a qualitative comparison of measuring instruments - accuracy, precision and trueness.

Trueness refers to the closeness of agreement between the arithmetic mean of an infinite number of repeated measuring results and the reference value, and thus indicates the presence of systematic measurement errors.

Precision describes the degree of agreement between measured values determined by means of repeated measurements on the same or similar objects under predefined conditions. The lower the variability of the measured values, the greater the precision and the probability that barely any outliers occur.

Accuracy is used to describe the range of values within which, with a certain probability, the true value of the measured quantity lies.

ifm sensors are characterized both by a high accuracy over the entire measuring range and a high precision. Due to the large number of tests our measuring instruments undergo, systematic errors, e.g. contamination or temperature influences, are compensated for and reduced significantly.

Question 6

How many calibration points do I need for my application?

Accepted Answer

Often, the position and number of measurement points for the calibration of a measuring instrument are not specified by a standard. In those cases, close coordination between the calibration laboratory and the user is necessary to define suitable test points. However in principle, the following applies: The larger the measuring range, the greater the risk of a calibration that is performed too superficially. Calibration should therefore always be based on the application and process parameters in question.

However, some types of instruments are standardised and specified by guidelines, for example, the calibration of pressure gauges (DKD-R 6-1). Such requirements describe the exact number of calibration sequences for different accuracy classes before the actual measurement is performed.

The following is an example of the measuring results from one of our calibration certificates for the SD5000:

Calibration service FAQ