ORIGINAL ARTICLE
One type of electromagnetic fields, based on frequency range, is Extremely Low Frequency (ELF) fields. There are lots of reports about measuring ELF-magnetic field (MF) in substations, power plants, cities and etc. This study aimed to compare the difference between measurement of three-axis and single-axis probe MF meters. ELF-MF was measured by TES-1394 MF tester (three-axis probe) and HI-3604 ELF survey meter (single-axis probe) in selected power plant and the resultant of three MF components (X, Y, and Z) was calculated based on equation. Field measurement was based on IEEE std 644-1994. In the generator building, minimum, maximum, and mean values of the magnetic flux density measured by the three-axis device were greater than those measured by the other two methods. Besides, the maximum value of the resultant method was greater compared to the measurements related to the other two methods, but the means of magnetic flux density by the three-axis device was greater than the resultant and maximum axis value. However, a significant difference was found between the maximum axis value and the results of the three-axis device (P=0.022). The best and most reliable way to measure MF is using a device with a three-axis probe and measuring the maximum MF by the singe-axis device cannot be reliable. Moreover, in the absence of a device with a three-axis probe, if there is a single-axis probe, the best we can do is obtaining the resultant from the three directions of the field.