General information regarding Calibration of measuring equipment
Often in daily use, no clear and consequent distinction is made between the terms calibrated and adjusted.
Calibration means to document the deviation of the measured value of a measuring device from a traceable, highly accurate standardized calibration standard. Here under specific reference conditions and reproducible measurement methods, the measured value of a measuring instrument is compared with the known value of a calibration standard.
Calibration does not mean that any interference in the measuring equipment is made, the measuring equipment remains unchanged.
Adjustment means setting or adjusting a measuring device to eliminate systematic measurement differences. Here under specified reference conditions, the measured value of a measuring instrument is adjusted to the value of a known calibration standard.
Adjustment is always an intervention that changes the measurement instrument permanently.
Traceability of calibration means the calibration chain is reproducibly documented from the measurement instrument to the national calibration standard of measure.
Traceability of measurement results is ensured by the metrological infrastructure of a country.
Why calibration of measuring equipment is required?
The standard for quality management systems DIN EN ISO 9001: 2008 Section 7.6 specifies essential requirements for monitoring of measuring instruments, as far as these are used to ensure valid results, and thus constant product quality. At specified time intervals, measuring instruments must be made traceable to national calibration standards and if needed re-calibrated and labeled so that the calibration status is recognized. If during calibration it is determined, that the measuring instrument does not meet the requirements, the company must assess the validity of the previous measuring results and take appropriate measures with respect to the measuring instrument and all products affected.
Periodic calibration thus is ensuring the product or service quality on the basis of internationally comparable measurement results. This creates legal certainty with regard to product liability and for acceptance tests and assessments.
For recalibration of measuring equipment, which in turn serves as standard - for monitoring of other measuring and testing, to ensure the traceability to national standards, a DAkkS calibration is recommended.
Factory calibration (ISO calibration)
Factory calibrations are frequently performed by manufacturers or non-accredited labs whose measuring equipment monitoring is subject to DIN EN ISO 9001: 2008. An external evaluation of the technical and professional capacity, as in accredited laboratories, is not necessary.
The contents of manufacturer's calibration certificates are harmonized with the calibration lab. Unless a recognized measurement method is used, the traceability of measurement results must be documented in the calibration certificate. The measurement uncertainty may be shown and there are normally the same criteria applied as for an accredited calibration. The lower processing and staff expenses incurred for this type of calibration are reflected in the lower price for this type of calibration.
Accredited calibration (DAKKS calibration)
The German Accreditation Body (DAkkS) is the national accreditation body of the Federal Republic of Germany for assessment, accreditation and surveillance of testing and calibration in accordance with DIN EN ISO / IEC 17025. The standard contains requirements for the technical and professional qualifications of the laboratory and its quality management system.
DAkkS calibration certificates can be issued following the requirements of the measured data comprised in the QM manual and published by the DAkkS accredited calibration laboratories only. Regular external reviews and reaccreditation guarantee a high level of quality, which is mainly achieved through traceable calibration standards, defined ambient conditions and measuring methods, as well as highly qualified personnel. The high procedural and personnel efforts lead to highly accurate measurement results, but they are also reflected in increased costs for the calibration.
An additional advantage of the accredited calibration is available due to the global recognition of DAkkS calibration certificates. It is a consequence of the multilateral agreements for mutual recognition of accreditation systems, that the European umbrella organization "European Cooperation for Accreditation (EA)" has established with the International Association "International Laboratory Accreditation Cooperation (ILAC)".
The period between two calibrations for measuring and testing equipment is referred to as calibration interval and must be set and monitored by the user according to his requirements. The main points for the determination of the interval are:
- Measurement value and permissible tolerance band
- Use of measuring and test equipment
- Frequency of use
- Environmental conditions
- Stability of previous calibrations
- Required measurement accuracy
- Company-specific requirements by the quality assurance system
For use under normal conditions, we recommend a calibration interval of 1 to 2 years. For measuring instruments, used for regular assessment, review of work safety, quality assurance of products and services, as well as under extreme environmental conditions, we recommend calibration after 1 year only.
The HILO-TEST GmbH measuring and testing laboratory at the highest level
Our laboratory is subject to the surveillance in accordance with DIN EN ISO 9001: 2008.
This guarantees product quality, competence of staff, continuous external monitoring and international recognition of calibration services.
Hilo-Test offers a factory calibration certificate (ISO calibration certificate).
The calibration certificate of HILO-TEST includes testing and recording of various measuring ranges and measurement uncertainty:
- voltage values
- current values
- time values
In addition, calibration date, serial number, reference conditions, information about the tester and permissible deviations are listed.
The scope of the calibration services of HILO-TEST includes:
- Entrance inspection to determine whether the device is within specifications
- Generation of a standard compliant calibration certificate
- Attaching a calibration mark with calibration date
- Replacement of the battery in battery-operated test equipment
- Cleaning of test samples