  The Beam Conditions and Radiation Monitoring System, BRM, is implemented in
CMS to protect the detector and provide an interface to the LHC. Seven
sub-systems monitor beam conditions and the radiation level inside the detector
on different time scales. They detect adverse beam conditions, facilitate beam
tuning close to CMS, and measure the doses accumulated in different detector
components. Data are taken and analysed independently of the CMS data
acquisition, displayed in the control room, and provide inputs to the trigger
system and the LHC operators. In case of beam conditions dangerous to the CMS
detector, a beam abort is induced.
  The Fast Beam Conditions Monitor, BCM1F, is a flux counter close to the beam
pipe inside the tracker volume. It uses single-crystal CVD diamond sensors,
radiation-hard FE electronics, and optical signal transmission to measure the
beam halo as well as collision products bunch by bunch. The system has been
operational during the initiatory runs of LHC in September 2008. It works
reliably since the restart in 2009 and is invaluable to CMS for everyday LHC
operation. A characterisation of the system on the basis of data collected
during LHC operation is presented.
