We might normally assumed that the metal componets of the spectrometer/microscope system are all at ground potential with no current flowing them. In fact small differences in potential of other of millivolts to volts, can exist between the components. The potential differences cause currents to flow in the range microampers to many ampers of high frequency ac current. These currents are commonly referred to as ground currents or ground loops. Figures 1, 2, 3 and shows example of ground loops. Figure 4 show shematic illustration of ideal ground paths in the SEM with EDS.


Figure 1: Electron-excited spectra of Mn showing Mn K alpha
- K beta peaks. Normal spectrum.


Figure 2: Electron-excited spectra of Mn showing Mn K alpha
- K beta peaks. Distorted with peaks introduced by severe
ground loop.


Figure 3: Electron-excited spectra of Mn showing Mn K alpha
- K beta peaks. As Figure 2, but an intermediate case.


Figure 4: Shematic illustration of ideal ground paths in a SEM
equipped with an X-ray detector.