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 condition using the welding current and the arc voltage at that current. The welding conditions could be taken from the welding procedure. Alternatively, a stable arc may be used with a mechanically held torch with or without arc voltage control. CAUTION Care should be taken to ensure damage does not occur to instrumentation. See Annex D for recommended precautions. A validation method for pulsed TIG power sources is recommended in Annex C.
.4 Metal inert/active gas and flux cored arc welding Metal inert/active gas (MIG/MAG) and flux cored arc welding (FCW) power sources usually have a constant voltage characteristic with a d.c. output. The voltage control may be scaled in absolute or arbitrary units.
The voltage control sets the no-load voltage, and the voltage will fall slightly as current is drawn (typically 3 V to 5 V per 1 00 A). Some power sources have a slope control that may be used to adjust the static characteristic and the setting of this control should be noted on the validation certificate. The voltage control if marked in absolute units should be validated at no-load voltages. An arbitrarily marked scale should be checked for reproducibility / consistency. MIG/MAG and FCW power sources do not usually have current controls. The output current of such a welding power source is generally controlled by the wire feed speed setting which is set on the wire feeder control panel. The current varies automatically to regulate the burn off rate of the consumable electrode. See Annex B on wire feed rate consistency and validate the wire feeder if necessary.
If accurate measurement of the welding current and voltage is required it is preferable to use an ammeter and voltmeter (fitted to the power source or separate) which can be calibrated or to use independent monitoring equipment. CAUTION Do not short-circuit the output of a constant voltage power source as a very high current will flow; use a load resistor. For synergically controlled and pulsed MIG power sources, a validation method is recommended in Annex C