Spot checks for consumption meters
The sample test for consumption meters is an official procedure for extending the calibration validity of electricity , gas , water and heat meters , in which a random sample is drawn from a lot . For this, compliance with special error limits is checked by a state-approved testing center. If fewer than a prescribed number of measuring devices fail the test, the calibration validity stipulated in the calibration regulations for all devices in the lot is extended by a certain time (e.g. five years for electricity meters, three years for water meters, four years for Gas meters), if necessary several times. The calibration stamp of the unchecked measuring devices is not renewed because it only documents the year of the last calibration and does not contain any information about the end of the calibration validity. The affiliation of each individual meter to a lot and its individual new calibration validity are documented in the test center for verification.
So it happens that meters are still officially calibrated and used in "business dealings" even after the (basic) calibration validity specified in Appendix 7 of the Measurement and Verification Ordinance (until January 1, 2015 Appendix B of the Verification Ordinance ) has expired may be.
Different meters of the same type and size may be combined in one lot, provided they are operated under comparable operating conditions (e.g. same water quality). In the gas supply, a lot may only consist of meters of the same design, the same manufacturer, and the same meter size.
The use of the random sample test must be reported to the calibration supervisory authority responsible in the respective federal state, which approves the extension of each individual lot on the basis of the test results communicated.
A description of the process e.g. B. for electricity meters with lot sizes, associated sample size and acceptance or rejection limit for electricity meters can be found in: Procedure for sample testing of electricity meters and additional electronic devices.