The pulse-height-analysis (PHA) system installed on the Joint European Torus (JET) measures the plasma soft X-ray emission (2-30keV) with an energy resolution of 450eV and a time resolution of 200ms. This diagnostic includes three Si(Li) detectors, equipped with sets of remotely controlled apertures and filters, which view the plasma in the midhorizontal plane of the torus along a single tangential line of sight. Automatic analysis of the spectra yields the central electron temperature (±10%), the central concentrations of chlorine, chromium, and nickel (50%, and Zeff (50%). Simulations of the measured spectra using a radiation code provides the basis to construct a consistent picture of the soft X-ray emission in the central region of JET plasmas.