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NEN-EN 12405-1 specifies the requirements and tests for the construction, performance, safety and conformity of gas-volume electronic conversion devices associated to gas meters, used to measure volumes of fuel gases of the 1st and 2nd families according to EN 437. This European Standard is intended for type testing, the detailed relevant provisions of which are given in Annex A. Only three kinds of conversion are treated in this European Standard: - conversion as a function of temperature only (called T conversion); - conversion as a function of the pressure and of the temperature with constant compression factor (called PT conversion); - conversion as a function of the pressure, the temperature and taking into account the compression factor (called PTZ conversion). This document is not relevant to temperature conversion integrated into gas meters which only indicate the converted volume. EN 12405-2 applies for energy conversion. Gas-volume conversion devices consist of a calculator and a temperature transducer or a calculator, a temperature transducer and a pressure transducer locally installed. For application of this European Standard, a conversion device may be, as a choice of the manufacturer, considered as a complete instrument (Type 1) or made of separate elements (Type 2), according to the definitions given in 126.96.36.199 and 188.8.131.52. In this last case, the provisions concerning pressure transducers, temperature sensors and temperature transducers are given in Annexes B, C and D respectively. Any conversion device can provide an error curve correction for a gas meter.