The ERMS will register the total count rate and also basic spectral information on the background radiation impinging on XMM and its science instruments. This is done not only during science observations, but during the entire lifetime of the mission. In this way, the ERMS monitors the total radiation dose that XMM is exposed to. When the level of radiation intensity exceeds a certain threshold, the ERMS issues a warning to the OBDH (Onboard Data Handler). Depending on the mode in which the ERMS is operated, it updates background radiation information once in 512 seconds (slow mode) or 4 seconds (fast mode).
The ERMS can also be used to predict the background in the X-ray instruments. The data consist of three measurements per readout, two spectra from the High Energy Detectors (HEDs) and one from the Low Energy Detector (LED). 256 spectral bins each will be available in the LED and HED. The HEDs are sensitive to electrons above 200 keV and protons above 10 MeV, while the LED is sensitive to electrons with energies above 50 keV.
The two high energy spectra are the ``HE detector spectrum'', with events from either one or both HE detectors, and the ``coincidence HE spectrum'', in which only events detected by both HEDs will be recorded.
The data from the ERMS comprise the following quantities: