Precise setting of a measured value by professional intervention in the measurement system. For balances: Either with an external test weight using the adjustment function (CAL or CAL key), or with the automatic internal adjustment or adjustment control. This is necessary following changes in temperature, changed environ-mental conditions, change of location, etc. daily routine checks are recommended. The term “calibrating” was formerly also used for adjusting., but today it means something else (see above).
Allowance for measuring uncertainty during practical use of a balance. Is given in the appendix to the DAkkS calibration certificate.
Calibration is the testing and determination of the precision of a measure value without intervention in the measurement sys-tem. The calibration certificate contains the measured value with information on the relevant measuring uncertainty. If appli-cable, a statement can be made as to whether this is within tolerance limits. Industry requires calibration of measuring devices, in order to, for example, be able to connect parts manufactured at different locations without encountering problems. Calibrations must be repeated at appropriate time intervals, for which the user is responsible. KERN recommends that, with intensive (daily) use, you recalibrate the measuring devices every 6 months and with normal (weekly) use, every 12 months.
Confirmation of the achievement or compliance of a predetermined standard, such as a DIN standard such as DIN EN ISO 9000 ff. (Quality management) or DIN EN ISO/IEC 17025 (Accreditation), or a build-type approval for balances.
Commercial error limit
Permitted tolerance (plus and minus) of measuring devices where verification is mandatory when used within their verification validity period. This tolerance is double the permissible error limit, in so far as this is not specified otherwise in the weights and measurers act.
Procedure for confirming warranted characteristics in accordance with recognised rules. For balances this relates to verification.
Conformity declaration from the manufacturer
The manufacturer declares that the product fulfils the applicable EU directives. With electronic balances this is always in conjunction with the CE mark.
Control of measuring equipment in the QM System in conjunction with quality standards
An organisation certificat to a quality standard such as DIN EN ISO 9001 ff. e.g. a production plant is obliged to adhere to a defined quality standard within the framework of its quality management system. To do this, it is imperative to have a measurement equipment which is working accurately. Chapter 7.1.15 "Resources for monitoring and measuring" of DIN EN ISO 9001:2015-11 states that measuring equipment must be calibrated at defined intervals and before use. The measurement devices and measurement standards needed to do this must:
- be traced back to international or national standards
- their uncertainty of measurement must be known - they must be marked with a clear identification
- the test must be documented
The DAkkS calibration fulfils all these requirements.
Every body experiences a relatively small loss of weight in air (buoyancy). This must be taken into account for accurate weighing procedures. In order to avoid this “distortion” in daily use, all weights are adjusted to the unit specifications as given in R111 OIML recommendation. (air pressure 1.2 kg/m³ and material density 8000 kg/m³)
DAkkS calibration is carried out for measuring devices, reference materials and material measures for particular measurement sizes and measurement ranges, which are defined individually for every laboratory as part of their accreditation. The issued DAkkS calibration certificates are proof of the metrological traceability to national and international standards, as required, for example, by the DIN EN ISO 9000 and DIN EN ISO/IEC 17025 standards. DKD calibration has no legally regulated period of validity. The operator is responsible for observing an appropriate time for recalibration. Usually the recalibration period is approx. 1 year.
DIN EN ISO 9000ff
Eichklassen von Waagen
Class I - analytical balance (precision balance)
Class II - precision balance
Class III - industrial scale (commercial scale)
External test weight
For adjusting or checking the balance accuracy. The external test weight can be DAkkS calibrated at any time, even afterwards.
Factory calibration certificates
The testing of measuring devices for accuracy in accordance with a recognised, but not accredited, process – this is the difference when compared with DAkkS calibration. ISO calibration certifi-cates are also referred to as factory calibration certificates.
Very important influence for precise electronic balances. Due to the varying influence balances have to be adjusted at the location of use.
Internal test weight
Like external test weight, but installed in the balance and powered.
International validity of DAkkS calibration certificates
DAkkS is represented in the EA (European co-operation for Accreditation) as well as in the ILAC (International Laboratory Accreditation Cooperation). This ensures that DAkkS calibration and DAkkS calibration certificates are recognised and valid almost anywhere in the world.
ISO 9000ff, DIN EN ISO 9000ff
Quality Management System in the form of a DIN Norm for quality assurance in a factory.
Greatest deviation of the weight displayed of a balance with regard to the value of the respective test weight in terms of plus and minus across the whole weighing range.
It is determined for each balance according to a precisely given test method and documented in the Calibration certificate. It depends on various factors, both internal and external. The measuring uncertainty of a measuring device is an objective measure of its accuracy and is therefore an accurate statement for its appropriate use.
Minimum load [Min]
Lower limit of the verifiable weighing range. Is markes on the verification mark. The function of the balance is also given below the minimum load.
Minimum sample weight
Indicates the smallest weight which can be determined, depending on the process accuracy required.
Newton (N) is the unit for physical force values. A Newton is the force required to accelerate a 1 kg mass at rest to a speed of 1 m/s within one second.
Neutral and independent, predominantly government bodies, which are formally apppointed by the EC. They are engaged in the field of verification for conformity evaluations (initial verification) and type-approval test within the scope of type approvals.
OIML (Organisation Internationale de Métrologie Légale) has representatives from almost 100 states who work on unified build and test regulations for all measuring devices. In the OIML certification system the certificates issued by the member states certify that a particular measuring device build type is in accor-dance with the OIML recommendations. In this way, a build type which was tested and approved in one country, can be approved in another country without having to repeat the test. (Excerpt from PTB). The OIML R111 guideline defines the construction-related characteristics for test weights, such as material, upper surface texture, markings, construction, shape etc.
Smallest readable weight increment on a digital display.
Reproducibility (standard deviation)
Sequenced measure of conformity in repeated weighing (e.g. balances) subject to the same conditions. Mostly 1 [d] or less. Quality feature.
Resolution of a balance
The resolution is calculated from the weighing range [Max] divided by the readout [d], e.g. [Max] 420 g:[d] 0.001 g = 420.000 points. The resolution is a quality feature - the higher, the better.
The pre-requisite for all perfect measurement is the complete, continuous proof, that a measuring device can be traced to international or national standards. The most important standards demand that all check ing equipment (e.g. test weights) meets the national or international standards in accordance with defined tolerances. In weighing technology, these standards are the test weights. They are traced back to the national test weight in the PTB (Physikalisch Technische Bundesanstalt) in Braunschweig, which in turn is derived from the original kilogram in Paris. In this way, incorrect measurements through inaccurate checking equipment is avoided.
Type approval for balances
Strict process to test whether a balance fulfils the verification requirements. A balance can only be verified, if it has got a type approval from a notified body.
A verification, called "evaluation of conformity" for new conceptuality, means the official examination of the accuracy of dimensions, weights, balances and measuring tools according to the law of dimensions and weight. The verification is required by the state and protects consumers. Only balances with approved design and only weights according to OIML of classes E2, F1, F2 and M1 can get a conformity assessment.
Verification validity for balances
Verification value [e]
Measure of the verification tolerance, depending on balance, mostly between 1 [d] and 10 [d].
Verificaton validity for balances
Generally 2 years for all verification classes, for control balances generally 1 year, after expiry the balance has to be re-verified.
Weighing range [Max]
Is the working range of the balance. The balance can be loaded up to the specified upper limit.