There are numerous types of “electronic loads”, but the 2 types of electronic load calibration we most frequently use to calibrate loads are test/calibrate welding rigs, and those used to
(i.e.: up to 60V and a few amps). The units used for welding rig calibration must handle high wattage for a few minutes but typically have a relatively low duty cycle. Electronic loads, such as those used for lab bench power supply testing, work opposite to power supplies. Instead of supply power they “pull” power. These types of loads can usually be programmed for constant voltage, constant current, or constant power, depending upon the need. I have experience with units capable of a hundred watts up to units that can pull 10,000 watts. These types of units are calibrated in different fashions.
Unless you have another specification causing the calibration frequency to be specified (some API specs call for 6-month calibrations on specific equipment), Gulf Coast Calibration suggests annual calibrations.
To calibrate welding rig loads, basically only the digital meters are calibrated, and other parts are checked to verify they are electrically connected and basically working. For this the ammeter is disconnected from its shunt resistor and a specific current is applied to the meter. The meter is adjusted, if needed, to match the input current. The same type of process is used to calibrate the voltage meter. Once this is done the unit is re-assembled. Now a reduced voltage/current is applied, and all the switch positions are tested to verify they get some reading. This verifies that the switch itself is good and that the circuits supplying the switch are connected.
For power supply type electronic loads, a known voltage or current is applied to the load, and the appropriate meter reading is adjusted as needed to be in tolerance. This is done for both voltage and current, typically for 2 points on each meter. After this basic functioning is tested, any special features are tested. All test points, and the readings taken at these points, are recorded on the worksheet. The worksheet is a major factor in Gulf Coast Calibration being consistent in how we test a unit now, and in the future, and in how we consistently test units, even from different manufacturers.
Whichever type of electronic load, after passing, it is labeled with the unit ID/SN, the date the calibration was performed, the expect next calibration date, and then initials of the tech that did the calibration. The unit is then packaged for return to the customer.