Non-automatic Weighing Instruments Calibration
Tests shall be carried out to verify compliance with the following requirements:
- errors of indication;
- accuracy of zero-setting and tare devices;
- eccentric loading;
- discrimination; not applicable for instruments with digital indication;
- tilt in case of mobile instruments; and
- sensitivity of non-self-indicating instruments.
Other tests may be performed in special cases, for example, in the case of unusual construction, doubtful results, or as indicated in the respective OIML Certificate (The International Organization of Legal Metrology [French: Organisation Internationale de Métrologie Légale]). The authority responsible may, in special cases, require the applicant to supply test loads, equipment and personnel to perform the tests.
For all tests, the error limits to be respected shall be the maximum permissible errors upon initial verification. If the instrument is to be shipped to another location after initial verification, the difference in local gravity acceleration between the locations of testing and use shall be considered appropriately, for example, by a second stage of initial verification after adjustment or by taking into consideration the local gravity value of the location of use during initial verification.
Weight or Weight Set Calibration
Two methods are used for the determination of the conventional mass of weights in a weight set:
- The direct comparison method; and
- The subdivision/multiplication method, which applies only for a set of weights.
Three different weighing cycles are described, all of which are forms of substitution weighing intended for, but not limited to, single-pan balances. Prior to mass determination, the density of the weights must be known with sufficient accuracy. In addition, the environmental conditions and the metrological characteristics of the weighing instruments used in the mass determination must be known with sufficient accuracy. Formula for the determination of the conventional mass and its uncertainty are given.
Accuracy Class: Class designation of a weight or weight set which meets certain metrological requirements intended to maintain the mass values within specified limits.
Conventional Mass: Also called the conventional value of mass. Conventional value of the result of weighing in air, in accordance with OIML D 28 Conventional Value of the result of weighing in air. For a weight taken at a reference temperature of 20°C, the conventional mass is the mass of a reference weight of a density of 8000 kgm-3 which it balances in air of a reference density of 1.2 kgm-3.
Standard Weight: Any weight whose mass is given. Since weights are not always available with documented corrections, weights defined by class may be used if the class chosen has sufficiently small limits and there is an understanding that errors perceived as being instrumental in nature could be attributed to incorrectly adjusted weights.