EVS-EN 12261:2018

This European Standard specifies the measuring conditions, requirements and tests for the construction, performance and safety of class 1,0 axial and radial turbine gas meters with mechanical indicating devices, herein after referred to as a meter(s), having in-line pipe connections for gas flow measurement.
This European Standard applies to turbine gas meters used to measure the volume of fuel gases of the 1st and 2nd gas families, the composition of which is specified in EN 437, at maximum working pressures up to 420 bar, actual flow rates up to 25 000 m3/h over a gas temperature range of at least 40 K and for a climatic environmental temperature range of at least 50 K.
This European Standard applies to meters that are installed in locations with vibration and shocks of low significance and in
-  closed locations (indoor or outdoor with protection as specified by the manufacturer) with condensing or with non-condensing humidity
or, if specified by the manufacturer,
-  open locations (outdoor without any covering) with condensing humidity or with non-condensing humidity
and in locations with electromagnetic disturbances.
Unless otherwise specified in this standard:
-  all pressures used are gauge;
-  all influence quantities, except the one under test, are kept relatively constant at their reference value.