BS EN 50504:2009 pdf download – Validation of arc welding equipment Welding power sources may have analogue or digital meters fitted. The general practice is to fit arithmetic mean instruments on direct current power sources and r.m.s. instruments on alternating current power sources. Arithmetic mean analogue instruments measure the average or mean value of the instantaneous parameter with respect to time. r.m.s. analogue instruments give an indicated rather than a true r.m.s. reading, see 9.3. Digital meters may give true or indicated r.m.s. readings. For some equipment a single digital meter may be used to measure a.c. and d.c. voltage and current. Expert knowledge may be required to validate such equipment and the manufacturer should be consulted. The standard methods of measurement are as follows: a) d.c. welding supplies shall be measured with averaging techniques; b) a.c. supplies shall be measured with root mean square methods using true r.m.s. meters or using indicated r.m.s. meters (i.e. assuming pure sinusoidal form). NOTE For power sources with non-sinusoidal waveforms e.g. square waves, averaging techniques may be used and the manufacturer should be consulted (see 9.3). 8.2 Manual metal arc welding with covered electrodes Manual metal arc (MMA) power sources have a constant current characteristic with a.c. or d.c. output. The current control if marked in absolute units should be validated at conventional load voltages. An arbitrarily marked scale should be checked for consistency. The MMA process is often controlled by measurement of run-out length where measurement of welding current is not necessary. However, if accurate measurement of the welding current is required it is preferable to use a calibrated ammeter (fitted to the power source or separate), or to use independent monitoring equipment. MMA power sources do not have voltage controls but could be fitted with voltmeters, which can be calibrated. 8.3 Tungsten inert gas Tungsten inert gas (TIG) power sources have a constant current characteristic with a.c. or d.c. output. The current control should be marked in absolute units and can be validated at conventional load voltages. Generally, TIG power sources are fitted with ammeters and possibly voltmeters, which can be calibrated. TIG power sources do not have voltage controls TIG welding power sources are used in complex TIG welding systems and it may be required to validate the system with load conditions, which closely duplicate the arc load conditions. The resistance of the load is calculated for a specific welding...
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