[en] Iron ion resonance-line intensity measurements are described as a representative sample of spectroscopic diagnostics of tokamak plasmas. A brief outline of the tokamak discharge characteristics is followed by a description of the spectrometer, and its calibration for absolute intensity measurements in the vacuum ultraviolet wavelength region. Then iron ion resonance lines in the wavelength range 90-360 A, from ionization states FeXV through FeXXIV, are shown as observed in the PLT tokamak. A discussion of the principal excitation processes leading to the emission of these lines in tokamak-type plasmas, and of the appropriate atomic cross-sections and rate coefficients, is then followed by quantitative measurements of these emissions in time and space in a PLT tokamak discharge. The results are interpreted in terms of iron ion concentrations, their behavior in the discharge, and their implications to radiative energy loss, contributions to electrical resistivity, and ion confinement times in the plasma